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THE USE OF ENDOGENOUS AND EXOGENOUS RESOURCES DURING THE EARLY DEVELOPMENT OF:-\ TLANTIC REDFISH (5iehustes spp.)

hy

Iknjamin J. l.aurd

:\ thl!sis submitt~.:d lO the School of (lraduatl.! Studi~.:s in partial fullillmcntuf th~.: r~.:quircm~.:nts for the degree of \tasters of Science

St. John's

Biopsychology Programm..: ivkmorial Lniv~.:rsity of Ncv.-foundland

August 1998

Newfoundland Canada

Abstract

Atlanti~ re<..ltish (5iehastes spp.) an.: a commercially exploited groundtish in the

N W Atlantic. yet little is known abolll the early life history of these species. Their

ovoviviparous reproductive strategy and restriction tn 1.kep benthi~ environments Juring

spawning makes stud~ ing embryogenic and lal\ al stages difticult. Proper management

of exploited tish sp~.:cie s . however. depends upon a comprd1ensiv~.: understanding of early

dl.!wlopmcnt as it is Juring the egg and lar\al stages that recruitment variability is

considl.!red to be largely determined. I conducted two separate irnestigations describing

the usc L>f endog~.:nuus and exogenous resoun:~.:s in larval r~.:dtish in an ath:mpt to both

provide insight into recruitment processes as wdl as un<.h.:rstand the evulutionary :-~uccess

of these species.

lhe lirst study examined changes in lipid and fatty acid protilcs in developing

pre-extruded larvae . During d~.:vdopment within the ti:malc then.: was nearly a 50°'i)

rcdw.:tion in total lipid. suggesting that lipids me an important source of l.!nergy and that

metabolism of these resoun.::cs m:curs prior to parturition. l'riacylglycaul was

prdcrl.!ntially cataboliscd ov~.:r polar lipids unlik~.: other Atlantic groundtish Juring

embryogenesis such as end ( CJadus nwrhua) and halibut (flippoglossus hippo~lossus ).

lligh variability in these lipid n:serv~s suggests that sensitivity to mismatches in prey

atter parturition likely varies between broods. assuming increased endogenous rcsourc~.:s

reduces risk or starvation.

The second study investigated behaviour. grO\.,.th and survival of larval redtish

reared under prey densities ofO. 500. 1500 and 4500 prey L- 1 in laboratory conditions.

ii

Somt: lm·vat: livc:d to day 18 in tht: 0 prey L·' treatment <.kspitc;: possible;: handling stress

from collection and transporting. Growth. survival and condition of larvae varied with

prey conct:ntration but \vere highc:st in the 1500 prey 1: ' treatment. The signiticantly

lovver prey bitc::oricnt ratios in the 4500 prc:y 1: ' trc:atmc:nt suggc:st that laf\.ac may ha\·c

become: confused at highc:r prey dc;:nsities. :\ pl)Ssiblc;: confusion effect may have:

c:xplaincd the signiticant reduction in grm\lh and survivalnf larvae reared in the highest

prey tn:atmcnt. :\!though the prey densities used in this experiment arc higher than those

n:portcd in the tidd. comparisons with other rearing cxpc:rimcnts suggc:st that prey

availability may not be as limiting tl) n:dlish as t'nr uthcr cnmmen.:ially important species

such as :\tlantic cod.

iii

Acknowledgements

I would like to thank my Sup4..!rvisor. Dr. Joe Brown. as \Veil as my Supervisory

Committ~t!: Dr. Bill Montcv~cchi and Dr. Rl)bin Anderson ti.lr all thl.!ir hdp and

direction . This thl.!sis would not have been possible \Vithout thl.! tinancial support of thl.!

\tultidisciplinar) Rcdtish Program tMRPl and a Biopsychology <.lraduate Stutknt

Fellowship.

A long. Jist of p~ople hdp~d with this r4..!sl.!an:h I am esp~cially indebted to l"cri

Stuckkss for carrying. llUt lipid and fan: acid analyses umkr thl.! supervision of Dr. Chris

Parrish. Rl.!aring larval lish was not possibk without the hdp of many other pt!ople

involved in live lood production. algac culturing.. maintenance and mutinc monitoring. .

would likl.! to thank Danny Boyce. Dena \Viscman. Donna Summerton. Trevor "-eog.h.

Ralph Pynn. Ross Wilson ;.md the wmkshop crcv. at the Ocean Sciem:cs Centre for all

their help and effort . Thanks also go to V. Puvanendran tor bs i.H.hice and patience to

my cndkss line or questions.

Lastly. l"d like to thank Louise Copeman. Garreth ··Loader .. Lawson. Stcphane

··The Windmill .. Uauthil.!r. and Crazy Dave Robichaud lor giving me something. to do

besides \Vatch Saturday night episodes of Xcna. Most importantly. thanks to my mother

and father in Minnt!sota for all their emotional and tinancial support.

iv

Table of Contents Page

ABSTRACT ii

ACKNOWLEDGMENTS i\-'

LIST OFT ABLES vi

I 1ST OF FIGURES viii

1.0 INTRODL'CTION

l . 1 Redtish b:ology 1 1.2 Endogenous Rcsourc~.:s 4 1. 3 E:mg~.:nous Resources 5 1 A Objectives 6

2.0 CHANGES IN LIPID AND FATTY ACID COMPOSITION OF PRE- 7 EXTRl1DED REDFISH THROli(;HOL'T EMBRYO<;ENESIS

2.1 Introduction 7 2.2 :\latcrials and Methods 9

2.2.1 Luval Colkction 9 2.2.2 Lipid/ Fatty ..\cid .-\nalysis It

2.3 Results 12 2.3.1 Lipid Classes 12 2.3.2 Fatty Acids 19

2A Discussion 19

3.0 BEHAVIOUR, GROWTH AND SURVIVAL OF REDFISH LARVAE 30 IN RELATION TO PREY AVAILABILITY

3 .I Introduction 30 3.2 Matt:rials and Methods 32

3.2.1 Larval Collection 32 3.2.2 Experimental Design 33 3.2.3 Data Analysis 35

3.3 Results 37 3 A Discussion 64

4.0 SUMMARY AND FUTURE RESEARCH 75

LITERATURE CITED 78

v

List of Tables Page

2.1 Description of developing pre-extruded redtish stages based on eye I 0 Jiameter. total length and pigmentation patterns.

2.2 Lipid composition of dev..:loping pn.:-extruded redtish larva.: expressed 16 as a percentage ot"dry weight (OW)± SO. Values based on samples (n) 0f 10 pooled eggs 0r pre-extruded larYac .

23 ! .irid ~()mrn-.iti(m nf redti~h larva..: '-'xrrL·-:-:ed as a percentage t'ftotal 17 lipid± SO. Valut:s based on samples (n) of 10 pookd eggs tlr pn:-extruded lal\-at!.

2A LipiJ composit[on of rcdtish larvae expressed as absolute amounts± SO. 18 Values based on samples ( n) of I 0 pookd eggs or pre-extruded larvae.

2.5

3.1

3.2

Fatty acid composition of total lipids throughout devdopment of pre­extruded n:dlish lal\-ae.

Operational <.ktinitions of the MoJal Action Patterns (MAPs) nbsel\-·eJ in Jevdoping redtish larvae.

Summary of t\NCOV A results on sv. imming and fnraging MAPs of larva..: at di ftcn:nt prey concentrations.

21

36

38

3.3 Tukey · s paif\vise comparison of (a) mean freqw.:ncy of total foraging -46--n M:\Ps and (b) orient fn:qu..:ncy in larval reJtish exposed to 0. 500. 1500 and 4500 prey l:' throughout a six week expt:rimental period. Significant differences occur wht!re 0 I ies outside the range of listed confidence intervals of each test. *Signilicant diftcrencc ( p < family l.!rror rate of 0.05 ).

3A Tukey· s pairwise comparison of bite frequency in larval redtish exposed 48--49 to 500. 1500 and 4500 prey L ·I throughout a six week experimental pt:riod. Signiticancc ditTcr!.!nces occur v.:hl!re 0 lies outside the range of listed confidence intervals of each test. *Signiticant differen~e (p < family ~rror rat~ of 0.05 ).

3.5 Tuk~y· s pail\-visc: comparison of mean duration spent motionless in larval 50" 51 redtish exposed to 0. 500. 1500 and 4500 prey L·' throughout a six week experimental period. Significance difterences occur where 0 lies outside the range of listed contidence intervals of each test. *Signiticant difference ( p < tamily error rate of 0.05 ).

vi

3.6 Summary of ANCOV A results for morphom~tric and condition chang~s 59 of r~dtish larvae at different prey concentrations.

3. 7 Tuk~y· s pairwise comparison of condition of larval redtish exposed to 0. 60-61 500. 1500 and ~500 prey L·' measured at the Jay intervals. Significant diff~rences occur where 0 lies outsiJ~ the range of listed contiJence intervals of each test. *Signi tic ant di ftl:rence ( p < family error rate of 0.05 ).

3.8 Tuk~y·s pairwise comparison nf(;.l) standard length 1SI.l anJ lhl ll2-63 myotome h~:ight nf larval n:Jtish cxpos~d to 0. 500. 1500 and ~500 prey 1." 1 m~asur~d at tin! Jay intenals. Signilicanc..: diff..:renccs oc~:ur \\h~o:n: 0 li~:s outside the r:1nge of listed confiJ..:nce intervals of each t~st. *Significant difference lp <. family error rate of0.05).

vii

List of Figures

2.1

2.2

2.3

Changc:s in dry weight ( DW) throughout the development of prc­extrwkd redtish larvae. Values arc mcans ( : 2 SE) of 5 samples comprised of I 0 larvae or eggs.

Changcs in °o dry \Vcight {OW) composition oftriacylglyc~.:rol CL\G) and phospho I ipid ( P L) throughout the l.kvdopmcnt of pr~.:-~.:xtrudcd rcdtish larvae. Data prcsentt!d as mean(::: I SE) of 1-5 sampl~.:s nf I 0 p1'Pkd ~.?g_g_S or brY:.le.

Changes in absnlute amounts oftotallipid. triacylglyccrol (L\(]) and phospholipid ( PL) throughout the devdopment nf pre-extruded redtish larvae. Data presented as mean(± I SF) of 1-5 sampks nf I 0 poukd r.:g.gs or larvar.:.

Page

13

1-l

15

2A Changes in total percent lipid ~.:omposition of sterols ( ST) throughout 20 the de\clopment of pn:-extrudr.:d redtish larvae . Data presented as mean (± I SF) of 1-5 samples of 10 pookd eggs or lan:ae.

3.1 f-oraging fre4uency ofn:dlish larvae in varying. prey concentrations -lO--ll tl\W time: a) orient frc4uem:y and h) bite frc4uency. lach week is <.:omprisc.:d of three days of observations taken every other day. Values arc means for each treatment per observational period · I SF: n == ]0 larvae pc.:r wt:ek.

3.2 Foraging frc4uem:y of redlish larvae in varying prey concentrations -l2--l3 over time: a) bite:orient ratios expressed as a percentage and b) total loraging fre4w.:ncy (orient .,.. tixate +bite). Each wc.:ek is ~.:omprised of three days of observations taken c.:vcry other day. Yaluc.:s arc means for each treatmc.:nt pc.:r obscrvational paiod · I SE: n = 30 larvae pcr wcek.

3.3 a) Swim fn:qucncics and b) motionkss duration of rcdtish larvae -l-l--l5 subjected to prey concentrations of 0. 500. 1500 and ~500 prey r.· 1 over time. Each Wt!ek is comprised of three days of observations taken cvt!ry other day. Valut!s arc means for each treatment per observational period ~. I SE: n == 30 larvae;: per week.

3.-l a) Mean standard length (SL) and b) mean myotome ht!ight (MH) of 53-5-l larval redtish subjected to prey concentrations of 0. 500. 1500 and ~500 prey L- 1 over time. Values arc means tn == l 0) : l SE.

viii

3.5 Mean grmvth rates (mm SL d- 1) (a) and mean condition index (MH/SL) 55-56

( b l of larval n:dtish subjected to prey concentrations of 0. 500_ 1500 and -l500 prey L- 1 over time. Values arc means (n = I 0) : 1 SE.

3.6 Mean orient frequency (a) and mean total foraging (b) of larval rcdtish 57-58 subjcctl.!d to prey concentrations of 0. 500. 1500 and -l500 prey L - I as a function of mean larval size (myotome height). Myotome height valu...:s arc ml.!ans (n=IO) takl.!n every tin~ Jays and bl.!havioural valul.!s arc means taken± 2 days of size values (n=20-30).

3.7 \kan bite:oricnt frequency of lan·al rcdtish subjected to prey 65 concentrations of 500. 1500 and -l500 prey L' 1 as a function of mean larval size (myotome height). Myotome height va!ul!s an: means (n=IO) taken every live days ami bchaviLmral \alucs arc m~:ans taken± 2 days ofsizc values (n=20-30).

3.8 a) Percent sun·ival and b) ml.!tamorphosis ofrcdlish larvae in prey 66-67 concentrations of 500. 1500 and -l500 prey l.- 1 at day 35. i\ktamorphosis \·alul.!s arc t:xprcssed as a percentage of lan·ae showing signs of either prc-llcxion or lkxion. Survival is the average of two replicates · I SE.

ix

1.1 Redfish Ecology

Chapter 1

General Introduction

R~tilish (.'iehustes spp.) ar~ long-liv\!J. ~omm~n.:ially important gmundlish sp~~i~s

in th~ ~W :\tlanti~. Th~y hav~ oflcn h~~n r~porh:J tt) lin: ~0 or 50 y~ars hut in som~

i nsli.m~es I ish ha\ e b~~n n:port~J to h~ in ~:\.~ess of XO y~ars ( Sl:ott and S~tm 19XX ).

Thre~ spe~ies of r~dlish ~urr~ntly reside l)IT th~ N~\\ founJianJ ~oast: the Jccpwat~r

h~ak~d r~Jtish (.\'ehastes meme/la). th~ .\~adian h~akcJ n.:dtish (.'.'ehwNs/i.t.\dutus). and

th~ Atlanti~ golden n.:dtish (."-,'ehustes marinus) . \'. marinus is thl.! largl.!st of thl.! thn.:c

sp~~i~s and can be id~nti ti~d based on its e:\.t~mal morphology (Scott anJ s~ott 1988 ). S.

faciallis and S. memella. ~ollt:ctivdy known as the bt.:aked rt.:dtish. arc not l.!asily

distinguished from ont: another unlt.:ss int~mal morphological ditTcrt.:nces in the swim

bladder art: ust:d ( N i 1981 ). Bottom-trawl surveys around the Flemish Cap and tht: Gul r

of St. Lawrt:nl:t: have shmvn .<;,·. men/ella and .\'. Ji.rciallls to bt: the most abundant redlish

species with the former being the most numt.:rous of the t\vo ( Ni 1981: Konstantinov

1985: St-Pierre and Lafontaint.: 1995 ). Because of their morphological and lit~ history

similarities. however. these thn.:e spccit:s ofredlish have bct:n traditionally managed as

one stock by the Department of Fisheries and Oceans (OFO) in Atlantic Canada.

The ovoviviparous rcproductivt: strategy of Sehustes spp. makes them unique

among co-occurring groundlish species in the NW Atlantic. The evolution and ecological

signiticancl.! of live-bearing in tishes has been reviewed by Wourms ( 1981 ). but very little

is kno\vn about Atlantic redtish. Although th~' energetic costs to the female are unknown.

live-bearing in fishes may contribute to increast!d lan·al survival by providing a

thermostatic cnvironment devoid of predators during vulnerabk pl.!riods in Je\dopment.

Larvae of live-bl.!aring. species may also bendit hy bl.!ing ahlc to usc dl.!ad broodmatl.!s as

an additional enl.!rgy source during emhl") ogenesis ( Buehll.!rt ct al. 1986 ). Lastly. it has

been suggested that n:dtish may usc this rcproducti vc strategy to time the n.:kasc of their

yuung in n.:sponst: to ideal feeding wnditions (Rung.~.: and dl.! Lafontaine 1496).

lloWI.!\I.!r. studil.!s hav~.: y~.:t to determine if such a bdla\ior actually ~.:xists during times uf

'al")ing food availability.

On thl.! l:ll.!rnish Cap . . '.·. mcmc:lla spawns from :\prilto early June while spawning

oL'i.ji.lsc:iaws pl.!aks in June and continul.!s into latl.! August (PI.!nney 19S7). In th~.: Gulf of

St. Lawrence. however. peak spawning of the beaked n.:dtish r.\'. me: mel/a and S.

ji.1sciarus) overlap hctw~.:cn April and June ( St-Pic.:rrl.! and Jl.! Lat4..mtainc.: 1995 ). The

fecundity of S. ml!nrella has hec.:n cstimat~.:d to vary betwc.:c.:n 1500-70000 OlH.:ytes pc.:r

l~male dl.!pc.:nding upon age.: \vhik estimates an: slightly higher tor .\'.ji.1sciatus tSt-Pierre

and Lat(mtainc 1995 ). Although these fecundities an.: relativdy lmv compan.:d to most

oviparous marine tish. late spring. spa\',:ning. .','i!has/l!s spp. comprise more than 80% of the

icthyoplankton off the northeast coast of Ne\vloundland (Anderson and Akenhead 1981 :

Anderson 1994) while ichthyoplankton surveys in the Gulf of St. Lawrence estimate.:

representation at greater than 96% (Runge and de Latontaine \996 ). The dominance of

larval Sehusres spp. during spawning also coincides with a spring bloom of planktonic

copepods. namely Calanusjinmarc:hicus. In the form of eggs and early nauplii stages.

tht:se ( 'alanus_linmarc:hi<:us s~rve as th~ prett:rred prey it~:m to n~:\vly extruded r~:dtish

larvae (Bainbridge and McKay 196&: :\mkrson 1994 ).

Despite the commercial importance of n:dtish. th~ early life history of th~:se

specil.!s is virtually unknov.:n. Undl.!rst:mding the rl.!pruduction and early lift: stag~:s of

commercially e~ploitl.!d marine tish spe~.:ics is crucial for t:fl~cti\t: tishcries management.

I! jon ( 19 14) tirst proposl.!d thut rccrui tmcnt was largd y determined as a rcsul t t> f

successful kcJing in lan·al tish during the switch bdwecn cndogl.!nous to cxogcnous

!~cuing. Termed the ·critical period" (May 1974 ). studies havc shown that high

mortalities oc~.:ur whcn suitable amounts of ti.>Od arc not availabk atkr ~ndogcnous

cncrg: n:scrn:s ar~: c~haustcd (e .g. Blaxter and I kmpd 1963: Lasker ct al. 1970).

l'hc critical pcriod concept is un underlying component of thc match,- mismatch

hypothesis (Cushing 1990). It is widd y hyp(llhcsizcd that larval populations tlu~.:tuatc as

a n:sult t>finll.:rannual vari:.1hility in pl:.mktonic blooms during tish spawning (Cushing

1990: Anderson 1994: Runge and de l.ali.llltainc 1996: Gntceitas ct al. 1996). That is. thc

rdcasc nf tish larvae into the \Vater column either docs (match) Llr docs not (mismatch)

coincide \Vith a bloom of pn:t~rred planktonic prey spe~.:ies. whi~.:h in tum panly

dt:tl.!rmincs the strength of a particular year class. The degree to which a mat~.:h or

mismatch in prey potentially aft~cts redtish recruitment is dependent on the larva's access

to ( 1) endogenous resources li .c. yolk rcscrvt!s) and {2) exogenous resources li.c. suitable

prey).

3

1.2 Endogenous Resources

Endogenous energy reserves. namdy lipids. provide both metabolic and structural

re4uircments for devdoping embryos and pre-feeding tish larvae. Proteins (Cetta and

C apuzzo 1982) and free ami no acids ( Rlmnestad et al. !992) have also ht:cn shown to be

an important cncrgy source in some spl.!cies although these biochl.!micals arc considl.!n:J to

be of ksser importance than lipiJ metabolism in Je\cloping marine !ish.

l.ipiJs an: stored in the lipoprotein-yolk and. if present. singk or multipk oil

glohuks found within the yolk-sac. Lipid anJ fatty acid protiks of the yolks of eggs anJ

larva.: vary between anJ within !ish species by type as wdl as by absolute and rd.ltive

amounts . Certain lipiJ class...:s arlo! typically useJ for m...:tabolism (..:.g. triacylglyceml and

sterol/wax esters) while oth...:r classes arc olkn used as structural compon...:nts in

bil)membran~:s e.g. phospholipiJs (Sarg~:nt 1995). Larval.! proviJed with more

metabolic lipid rcservl.!s may then:fore be less sensitive l\.) mismatches in prcy as a n:sult

of having lower susceptibility to ddayed feeding . !!art and Werner ( 19X7) ti.)und that

white sucker larvae (Catostomus commersoni) had higher survival during th~: transition to

exogenous food than pumpkinseed larvae (Lepomis gihhosus) . This was attributed to

larger cgg sizes and yolk reserves in white sucker larvae than pumkinsecd larvae. In a

review by Milh:r et al. ( 1988). larva~.: with larger yolk sacs \vcrc generally tound to have

greater t1exibility in the time in which feeding switches from endogenous to exogenous

sources. This was evidenced by longcr times to tirst fecding as wdl as greater variability

in the timing of tirst feeding in larger yolk-sac larvae. Larger eggs (i.e. higher lipid

4

com~nt) also typically produce larg~r and fast~r growing htrvae (Moodie et al. 1989:

Bruv, n and Taylor 1992) which in tum should posi ti vdy affect survival through th~

increased foraging ability of largc:r. mon: Je\doped larvae ( llunta 1981: Brown and

Colgan 1985 ). Thus intc:r- and in~raspccilic variability in the c:ndogenous resources of

tish larva~ can have pronounced cfti:cts on behaviour. g.rO\vth anJ ultimatdy survival.

rherdl.He it is important to record these dcvdopm~ntal chang~s. noting ~specially

changes in lipid/ fatty aciJ protiks over time as \\ell as variability in these proliks

between specimens. Gathering baseline biochemical data ti.lr pre- and post-ti:eding. larvae

can be further used to calibrate condition indices (Fraser 19lN: l.ochmann et al. I 995) as

wdl as determine larval nutritional re4uin . .:ments (Watanabe 19lQ).

1.3 Exogenous resources

Fish larvae must obtain food ll.)r survival after endogenous food supplies an:

exhaust~.:d. Successful ti:eding is largdy determined by the li.mtg.ing ability of the lish

larvae within its prey environment. Foraging ability is depend~nt on ecological factors

(e.g. temperature. light and turhul~nce) as \Vel! as size anJ species characteristics and

development. Changing larval morphology and physiology (e.g. mouth gape and visual

acuity) and behaviour (e.g. swimming and searching ability) during growth and

development is also of great importance (Hunter 1981 ). W~ can therefore expect

different responses to matches and mismatches in prey for Jiftt:rcnt larval tish species.

By measuring physiological and behavioural responses to changing prey fields over

development. one can assess optimal and sub-optimal foraging conditions which may

affect survival between years.

5

Our current understanding of larval redlish tl!eding ecology is based solely lm

tield experiments using gut content analysis and ~.:stimated prt:y conc~.:ntrations. No

studies to date have successfully carri~.:d out experim~.:nts on captive redtish larva~.:. hut

this is not surprising considering the lit\: history ofth~.:s~.: specit:s . Redtish are extremdy

slow g.ro\\1-!rs. gnw .. ing. only to 19 em hy 5 y~.:ars and recruited into the population at 7-10

years of age llfl the Fkmish Cap (Lilly 19H7 ). Adult n.:dlish i.Ue typically found at depths

in exc..:ss u!"400 mt:t~.:rs (Lilly Jl)87). and this. coupkJ with their live-bearing natur..:.

mak..:s lanae retri~.:val logistically Jiflkult. tim~.: consuming and t:xpt:nsin:. P~.:nny and

hans ( 1985) \VI.!re abk to k~.:ep larva~.: ali\1.! for 12 Jays in aquariums. but insignificant

growth anJ high mortality caus~.:J them to Jiscontinue experiments. Methodologies for

related species such as .\'ehas/es murnwru111s. howe\~.:r. have been successfully

impkmcntl.!d for the aqum:ultun.: industry in Japan ( L3oehh.:rt and Yamada Jl)l} 1 ).

lA ObjcctiYes

This thesis will cover ~.:arty lite history aspects of .-\tlantic n.:dlish from the

embryonic stages to th~.: beginning ofjuvcnik metamorphosis. The tirst expcrim~.:nt \Viii

ducidat~.: th~: rol~.:s of ~:ndogcnous n.:sourccs in pr~.:-extruded larvae by way of lipid and

fatty acid analysis. The second expcrim...:nt \vill locus on tiJrag.ing behaviour. grmvth and

survival of larvae aftt!r parturition. While each experim~:nt addresses questions

indept!ndent of one another. speculation into the ecological signi ticancc or these results.

spcci tic ally issues of survival variability. wi II be emphasised in the last chapter of this

thesis.

6

CHAPTER2

CHANGES IN LIPID AND FATTY ACID COMPOSITION OF PRE-EXTRUDED REDFISH THROUGHOUT

EMBRYOGENESIS

2.1 Introduction:

Lipids hme been shm.vn to be an important energy source as wdl as key

components of membranes tor developing marine tish eggs and pre-feeding larvae. Free

amino i.H.:iJs also serve as an ent:rgy source to somc spccies but arc gcnt:rally of seconJary

importance to the mctabolism of lipiJs . One notabh: exception. howcvt:r. is tht: turbot

(.'•:coptlwlumus !1l£L"(imus) in \Vhich fret: amino aciJs account tor the majority nf fud for

energy mctabolism in early Jevclopment (RklnncstaJ ct at. 1992).

The polarity of t:ach lipid Jctcm1incs \Vhcthcr it is dasscJ as either polar or

neutral. Ncutral I ipids an: considered to be the most common source of energy. namdy in

th~: form of waxy esters or triacylglycerols CI'AG). High percentages nfT.\G an: often

found in lish eggs with long incubation times l(Jr the provision of enc:rgy prior to

exogenous fel:!ding ( Sargt:nt 1995 ). Polar lipiJs. however. arc considcrcd to be more

important for cellular structure than energy. In the form of phospholipids. polar lipids arc

essential for biomcmbrane formation because of their hydrophilic head group and two

hydrophobic fatty acid tails.

Recent evidence gathered on a wider range of marine tdcost eggs anJ larvae has

led researchers to reconsider the role of neutral and polar lipids. For example. halibut

7

eggs undergo a kngthy developmental period. yet have more than twice the percentage of

phospholipids to neutral lipids (Falk Petersen t:t al. 1986: Falk-Petersen eta!. 1989).

Similarly. cod (liadus morhua) have been shmvn to have nearly 10 times the amount of

phospholipids to neutral lipids during egg and early larval stages (Fraser eta!. 19R8).

These studies suggest that phospholipids may have a Jual function in both energy

production and biomembrane formatilm . Thcrcfore it would appear diflicult to pn.:dict

lipid pro tiles or pre\·iously undescribed specics l)r mar;ne tdcost eggs and larvae.

Conversely. the btty acid signatun:s show a fairly consistent trcnd among marine

tdcost eggs and larvae. Polyunsaturated fatty acids ( Plli-"A) comprise a high pnrtion of

the fatty acids prcsent in both the phospholipids and the ncutral lipids. particularly the ( n­

.3) PlJh\s 22 :6(n-J) <DHA) and 20:5n-3 (EPi\). Together these (n-.3) PUFAs both serve

in the devdopment of neural cdl membranes as \veil as provide energy for devdoping

marine tish larvae (Sargent 1995 ).

Nevertheless. spcculation into lipid and fatty acid compositions of undescribed

species should bc conduct..:d \Vith caution . Despite th~: tremendous amount of lipid data

gathered for marine tdeosts within the last two decades. research has tiJcused almost

entirely on species with an oviparous mode of reproduction. Fe\v. if any. studies have

collected lipid and fatty acid data on developing larvae in ovoviviparous species i.e.

species in which li!rtilization and embryonic development is internal. Energetic studies

within some ovoviviparous specit!.: have shov.n that maternal contributions to the embryo

can continue after oogenesis (MacFarlane eta!. \993: Boehlert et al. 1986: Boehlert et ai.

1984 ). As a consequence we may expect to tind lipid and fatty acid consumption patterns

8

to be vastly different in species emplo~ ing an ovoviviparous reproductive strategy.

Redtish (5:t!has/L's spp.) are ovoviviparous tekosts and arc an important

commen:ial groundtish species in the North Atlantic . . '1. memt!lla (deep-\vater redtish)

and .'1. _l(lsc.:iarus (Acadian redtish) are the most commonly exploited spccies in deep wuter

(>400 m) otT the Newfoundland coast. yet \\!ry little is knt)Wn about the early litl! history

of these tis h. The aim of this study is to gather baseline data and describe changes in

lipid and btty •lcid composition t)f pre-extrudt:d larval redlish tor the tirst time.

Comparisons between other oviparous marine tdeosts are conducted in an eft(.)rt to

further elucidate I ) the mles of speci tic lipids and fatty acids in develnpment and 2) the

maternal- ktal relationships associated with 0\"l}Vi \ i parity .

2.2 Materials and Methods:

2.2. I Larval Col/ec:tioll

Redtish larvae were gathered from adult females collected from bottom tmwl

surveys aboard a DFO research vessel otT the south coast of Newtoundland in N AFO area

3N. Adult tcmales were identitied as either S. ji.1sc:iatus or.\·. mente /Ia using extrinsic

gas-bladder musculature as described by N i ( 1981 ). Of the 12 tcmale redtish collected.

two were identitied as .'-). jl.lsciallls and I 0 were identitied asS. men/ella. Larvae or eggs

from each female were extruded onto foil shects and separated into one of tive

dcvclopmcntal stages based on morphometric and pigmentation characteristics using a

dissecting scope and digital calipers (Sec Table 2.1 for developmental definitions).

Although the presence of two developmental stages was commonly present within a

brood. only one was selected to represent each female. Serum and blood were gently

9

Table 2. I: Description of developing pre-extruded rcdtish stages based on ey·t! diameter. total length and pigmentation patterns.

Denlopmcntal Sta e

01

1..)2

03

1)5

Definition

Larvae arc unhatched (egg diamctt!r -1.6 mm) but eyes arc clearly visible through the chorion.

).U-5 .5 mm larva~: with large yolk sacs. Eyes arc 0.29-0.31 mm tn diameter and no pigmentation is visible along the hody .

6.0-6.5 mm lan·ac with large yolk sacs. Eyes arc larg~:r than 02 larvae (0.38-0.42 mm) but pigmentation is still absent along the body.

6.5-6.8 mm larvae with noticeably n.:duccd yolk sm:s from D2 and D3 stages. Pigmentation is present along the dorsolat~:ral surface of the gut and mdanophorcs arc punctate in shape. Eyes arc 0.5-0.51 mm in diameter.

6.8-7.2 mm larvae\\ ith wstigcs l)f yolk sacs remaining. Pigmentation is present along the dorsolateral surface of the gut as well as dorsally l)\Cr the.! hrain. Further pigmentation is seen along the dorso- and ventro-miJlincs. Mclanophores arc either stcllat~: or branched in shape.!. often connected \Vithin postanal areas. Eyes arc slightly larger (0.52-0.53 mm) than larvae in D4.

10

rinsed from the larvae or eggs using tiltered sem\atcr before being plm.::ed into 25 cl vials

containing chloroform. Samph: vials contained ten larvae or eggs from an individual

kmak and in no instances were t~males used for multipk sampling. However. it should

be noted that only one sample was gathenx.l for both developmental stages 1 and 5. Vials

wc.:re stL)red in chlorofom1 at -20° C until lipid and fatty acid analysis.

Dry \\eights m.-n: cakulatt:d from samples of redlish larvae pn:sern:d in ethanol

colb:ted on a previous sampling trip. Larvae were placed on pn:-wcighcd tiJils and

placcJ in a drying oven !'or a period of 2-+ hat 65° C. Ten larvat: \Vcre used tix each foil

and a total of live foils wen: measun:d fnr each Jen:lopm~:ntal stage. Foils wen: weighed

to the nearest 0.000 I mg using an electronic microbalance.

2.2.2 LipitVFatty Acid Atw(rsis

The extraction nf lipids was carried out using the methods dcscrib~.:d by Folch et

al. ( 1957) by homog~.:nizing samples in a 20 \'L)I of chloroforrn:mcthanol (2: I) and rinsing

with \Vater. Individual class~:s of lipids \vcrc quanti lied in triplicate by thin layer

chromatography with tlamc ionization detection crLC/FlD) using silica gd CO\t:n:J

quartz rods (Chromarods-SIIl) and a MARK V latroscan (Parrish 1<)87). Samples (0.5

j..lg) were spotted on rods and developed twice in h~:xane-Jiethyl cther-torrnic acid

(99:0.1 :0.05) for 20 and 25 min respectively. tollowed again by the same solvent at a ratio

of 79:20: I for 40 min. Finally. samples w·erc devdoped twice in a l 00% acetone solvent

tor a 12 min and then 10 min period. Chromatograms were combined and peak areas

were calculated using T-data scan software (RSS Inc .. CA. USA). Peaks of sample

chromatograms were identified using chromatograms ofTLC/FlD run standards to give

l I

absolute amounts of t!ach lipid class. Total lipid of t:ach sample \vas then determined by

summing the lipid classes and correlating these \Vith gravimetric lipid \Vcights ( Danielt!t

al. 1993 ).

Fatty acid mdhyll.!sters (FAME) \Vt:rc quanti tie<.! on a Varian 3-lOO GC cquippeJ

with an Autoinjector. The (iC was Iittell with an Omegawax 320 column (.:w m. 0.32

mm i.J .. 0 .25 ~Lm tilm thickness: Supl'lco. Inc.) with hyJrogen usc<.! as a carrier gas. Each

FAME \vas prepare<.! from ·- 1 mg of the total lipi<.ls using the catalyst Bf.l ,'Methanol.

This pruceJure follows tht.: methoJ oftht.: .. \merican Oil Chemists· Society (Ce lh-g9)

with cxception that hexane rcplact.:J iso-octane. The (IC ovcn \Vas initially set for 65° C

for 0 .5 min ramping to 195° C at -l0° C min· 1 and hciJ there fur 15 min. Final ovt.:n

tt.:mpcratures reached 220° Cat a rate of 2° C min· 1 anJ were ht.:IJ for 0 .75 min.

lnJividual FAME wert.: Jerivt.:J using Varian Star Integrator sothvart.: (Supeko stanJarJ).

2.3 Results:

2.3. 1 Lipid Classes

Dry weight Jecreased Juring t.:mbryog.enesis although this was most pronounced

hctween D4 and 05 (Fig. 2.1 ). The totallipiJ content during the late egg stage \Vas -18

'Yo of the dry weight and fell to just under 16 '%at the latest larval developmental stage.

Initially. TAG had tht: highest presence within the lipid classes at 58% of the total lipid

composition and I 0.6% of the dry \\·eight (Table 2.2. 2.3 ). Throughout development

TAG was catabolized and phospholipids (PL) became more highly represt:nted (Fig 2.2).

Absolute amounts of PL howt:ver. remained constant throughout development as

amounts of total lipid and TAG reserves depleted (Table 2.4: Fig. 2.3 ). In the last

12

-'7 Q) ('I]

2: ro 0> E -....

..c: 0> ·m ~

~ 0

0.40

0.35 --.;

0.30 ---!

0.25 -l

i 0.20 ' I

I

I ! I I

0.15 --1 I

I I I

0.10

0.05

0.00

0 1 2 3 4 5

Developmental Stage

Fig. 2.1: Changes in dry \veight (0\V) throughout the development

of pre-extruded n:dtish larvae. Values are means(± 2 SE) of tive sample

comprised of ten pooled larvae.

13

.l

-. +-' ...c 0>

.Q)

3: C'

""0

:::R 0 -c 0

:.;::; ·w 0 a. E 0 u

""0 ·a. ~

------ Phospholipid (PL) ------ Triacylglycerol (TAG)

12 ~---------------------------------------------.

11 -----10 ~

~

9

8

7 \ \

6 \ \

5 \

• 4 ~------~--------~------~------~------~------~

1 2 3 4 5

Developmental Stage

Fig. 2.2: Changes in the average percent dry weight composition of

triacylglycerol (TAG) and phospholipid (PL) througout the development

of pre-extruded redfish larvae. Data presented as mean (± 1 SE)

of 1-5 samples of 10 pooled eggs or larvae.

14

-.. ...--

I ro 2: ro 0> ::t ._.

"'0 ·a. ~

-e- Total Lipid --- - TAG __..__ PL

80 ~------------------------------------------~

70

60

50

40 ----+"" 30

20 ....-------+--'-........

~~~~--.. 10 "'.

0

0 1 2 3 4 5

Developmental Stage

Fig 2.3: Changes in absolute amounts of total lipid, triacyglycerol

(TAG) and phospholipids (PL) throughout the development of pre-extruded

redfish larvae. Data presented as mean(± 1 SE) of 1-5 samples of 10 pooled

eggs or larvae.

15

....... 0"1

Table 2.2: Lipid composition of redfish larvae a throughout pre-extruded development expressed as a percentage of dry weight (DW) ± SD. Values based on samples (n) of 10 pooled eggs or pre-extruded larvae.

HC:hydrocarbons; SE:sterol esters; KET:ketones; TAG:triacylglycerols; FF A:free fatty acids; ALC:alcohols; ST:sterols; DAG:diacylglycerols AMPL:acetone-mobile polar lipids; PL:phospholipids

Stage Total HC SE KET TAG FFA ALC ST DAG AMPL PL %DW %DW %DW %DW %DW %DW %DW %DW %DW %DW %DW

x 18.192 0.051 1.410 0.000 10.631 0. 173 0.000 0.489 0.253 0.597 4.599 (n=l) so na na na na na na na na na na na

2 x 19.857 0.117 1.333 0.000 10.676 0.147 0.031 0.696 0.188 0.574 6.098 (n=2) so ± 2.665 ± 0.045 ± 0.134 ± 0.000 ± 1.165 ± 0.096 ± 0.043 ±0.221 ± 0.064 ± 0.397 ± 0.675

3 x 19.615 0.109 1.186 0.000 9.285 0.094 0.021 0.986 0.221 0.582 7.134

(n=5) so ± 4.138 ± 0.055 ± 0.250 ± 0.000 ± 2.135 ± 0.025 ± 0.047 ± 0.286 ± 0.083 ± 0.238 ± 1.454

4 x 16.042 0.138 0.783 0.000 7.325 0.120 0.014 0.920 0.130 0.472 6.312 (n=3) so ± 1.628 ± 0.023 ± 0.060 ± 0.000 ± 0.795 ± 0.079 ± 0.025 ±0.105 ± 0.057 ± 0.116 ± 0.943

5 x 15.863 0.105 0.784 0.124 4.667 0.167 0.000 1.225 0.159 0.389 8.247 (n=l) so na na na na na na na na na na na

a Development stage 1 is an egg stage.

Table 2.3: Lipid composition of redfish larvae a throughout pre-extruded development expressed as a percentage of total lipid ± SD. Values based on samples (n) of 10 pooled eggs or pre-extruded larvae.

HC:hydrocarbons; SE:sterol esters; KET:ketones; TAG:triacylglycerols; FFA:free fatty acids; ALC:alcohols; ST:sterols; DAG:diacylglycerols AMPL:acetone-mobile polar lipids; PL:phospholipids

Stage Total %HC %SE %KET %TAG %FFA %ALC %ST %DAG %AMPL %PL Jl /larva

x 64.46 0.28 7.75 0.00 58.44 0.95 0.00 2.69 1.39 3.28 25.28 (n= l) so na na na na na na na na na na na

2 x 66.97 0.61 6.73 0.00 53.86 0.72 0.17 3.46 0.93 2.78 30.76 ....... (n=2) so ± 8.99 ± 0.31 ± 0.23 ±0.00 ± 1.37 ± 0.39 ± 0.24 ± 0.65 ±0.20 ± 1.63 ± 0.73 -.....)

3 x 60.08 0.53 6.06 0.00 47.27 0.52 0.08 4.99 1.23 2.90 36.43 (n=5) so ± 12.68 ±0.16 ± 0.60 ±0.00 ± 2.36 ± 0.24 ±0.19 ± 0.91 ± 0.65 ±0.94 ± 1.48

4 x 48.38 0.86 4.90 0.00 45 .70 0.72 0.10 5.74 0.81 2.96 39.21 (n=3) so ±4.91 ±0.06 ± 0.35 ±0.00 ±2.62 ± 0.45 ±0.17 ± 0.49 ±0.34 ±0.73 ± 2.10

5 x 33.11 0.66 4.94 0.78 29.42 1.05 0.00 7.72 1.00 2.45 51.99 (n= l) SD na na na na na na na na na na na

a Development stage 1 is an egg stage.

Table 2.4: Lipid composition of redfish larvae throughout pre-extruded development expressed as pg/larva a± SD. Values based on samples (n) of 10 pooled eggs or pre-extruded larvae.

HC:hydrocarbons; SE:sterol esters; KET:ketones; TAG:triacylglycerols; FFA:free fatty acids; ALC:alcohols; ST:sterols; DAG:diacylglycerols AMPL:acetone-mobile polar lipids; PL:phospholipids

Stage Total HC SE KET TAG FFA ALC ST DAG AMPL PL J.lg/larva J.lg/larva J.lg/larva J.lg/larva J.lg/larva J.lg/larva J.lg/larva J.lg/larva J.lg/larva J.lg/larva J.lg/larva

x 64.460 0.181 4.996 0.000 37.670 0.612 0.000 1.734 0.896 2.114 16.296 (n= l) SD na na na na na na na na na na na

2 x 66.965 0.395 4.497 0.000 36.003 0.497 0.103 2.3460 0.632 1.935 20.563 (n=2) SD ± 8.987 ± 0.153 ± 0.453 ± 0.000 ± 3.927 ± 0.325 ± 0.146 ± 0.747 ±0.216 ± 1.339 ± 2.276

......... 00 3 x 60.080 0.333 3.634 0.000 28.439 0.289 0.065 3.019 0.678 1.782 21 .850

(n=S) SD ± 12.676 ± 0.167 ± 0.765 ± 0.000 ± 6.539 ± 0.078 ±0.145 ± 0.877 ± 0.255 ± 0.728 ± 4.454

4 x 48.377 0.416 2.361 0.000 22.090 0.361 0.043 2.774 0.391 1.423 19.035 (n=3) SD ± 4.908 ± 0.068 ± 0.181 ± 0.000 ± 2.399 ± 0.239 ± 0.074 ± 0.317 ± 0.173 ± 0.349 ± 2.846

5 x 33.11 0.219 1.636 0.258 9.741 0.348 0.000 2.556 0.331 0.811 17.214 (n= l ) SD na na na na na na na na na na na

a Development stage 1 is a pre-hatch stage so numbers are reported as pg/egg rather than pg/larva

developmental stage. PL represented 52 %of the total lipids and accounted t(1r 8.3 °/o of

the dry weight \vhereas T:-\G shmved a 50 °'o reduction from D I.

Like TAG. sterol esters (SE) also became less represent..:d as the larvae d..:veloped.

SE accounted tor 7.8% of the total lipids at Dl and later fell to 5 °1o at 05 (Table 2.2). At

the sam..: time sterols (ST) increased in percentage of total lipid t'rom .2.7 °'o at Dl to 7.7

'Li1 at 05 (Fig .2.-l. Table 2.2 ).

2.3.2 Fatty .-tc:id.•i

The pn:dominant tatty a~.:ids in alltht.: Jewlopmental stages of pn.:.extruded

redlish \\ere 16:0. 16:1n-7. 1S:In-9. 20:1n-9. 20:5n-3 and 22:6n-3 tlabh.: 2.5). Ofthcsc

fatty acids. h~:xadecanoic a~.:id ( 16:0) \vas the most highly represented saturated acid while

cis-9-octadecl.!noi<.: acid (I R: I n-t>) and docosahexanoic acid ( 22:6n-3) were the major

monounsaturated and polyunsaturatt:d fatty acids n:spectivdy .

Slight changes appeared in the fatty at.:id ~.:omposition of larvae throughout

development Total PUFA incr~:ased - 4.6% alter D I and remained elevated throughout

D2-D5. Total monounsaturatcs declined throughout development from 3R . .2 °1(1 to 31.8 °'o.

this trend being most supported by the decline of 18: I n-9 from 16.7% to 13.3 %.

lncrcasl.!s in both 18:0 and 16:0 resulted in an overall increase of total saturates from 17.7

1Yo in 01 to 23.3% in 05.

2.4 Discussion:

There is a general decrease in lipid as a percentage of dry weight during

development. although this decrease is not evident from the transition of larvae from D 1

19

2

0

__._ 0/o Sterol

1 2 3 4 5

Developmental Stage

Fig 2.4: Changes in total percent lipid composition of sterols ( ST)

throughout the development of pre-extruded redtish larvae. Data

presented as mean(± I SE) of 1-5 samples of l 0 pooled eggs or larvae.

20

Tabk 2.5 : Fatty acid composition of total lipids throughout dcvdopment of pre-extruded red !ish larvae. Data are expressed as a mean paccntage of total fatty acid composition± SO. Values based on sampks ( n) of I 0 pooled eggs or pre-extruded larvae.

Fatty Acid

1~:0

I 6:0

18:0

rotul.\'llturute.'i

20:1 n-7

20: I n-9

22: I n-Il

TotalltWIWUII.'iaturute.'i

16:2

18:2n-6

20:4n-6

22:5n-J

22:611-J

Total n-J

Total PL-'FA

DEV I (n=t)

'., ~ t - · ·'

2.9

17.7

8.9

1.0

-U

16.7

1.0

6 .8

1.6

38 .2

. 1.0

1.3

· I .0

11.0

1.4

17 .6

30.0

31.3

DEV II (n=2)

2.5 :: 0 . .3

i3 .o ~ IJ . .::

3.-l ": 0.2

19.5 ± 0 .3

8.1 ± 0.5

1.0

..t .6 t 0. 1

15.0 +.: 0.5

1.0

6 .0:!: 0.3

1. 1 ±. 0 . 1

3-l .7 .!: 0.~

1.1 .t · 0. I

I A::· 0. 1

1.0

11.8 ± 0.7

1.3 ± ··-0. 1

20.-l ± lA

33 .~3±0.7

35 .9 ± 0.7

DEV Ill DEV IV (n=5) (n=J)

2.5 :: 0.6 2.8 ~ O.X

i 5.~ .!: 2.2 13.b :: li.~

3.7::0.3 3A ±: 0 .2

22 . 1 :: 2.-l 19.7 :!:' 1.6

7.8 :!:: 0 .5 8.9 ~ IU!

I .0 I .0

-U :: 0.-l ~ - 8 ::: 0. I

13 .9 +.: 2 .8 15.1.:1.9

1.0 1.0

5.3 t 0.9 o .ll ± 1.6

1.0 1.0

32.9 ± 2.9 35 .6 ± 3.3

0.7 ± 0.7 1.0

1.3 ± 0 .2 1.3 ± . 0 . 1

i .O 1.0

I I.~ ± 1.2 I I. 9 ±: 0. 9

1.0 ± 0 .6 1.3 ± 0.2

19.7:!: 2.3 18.3:!: 2.0

32 .5 ± 3.5 31.41 ± 2.7

3-t7 ± -4.0 33.1 ± 2.2

21

DEVV (n=l)

, ' __ _,

i 7 . I

3.9

,, ' _ _, _ _,

8.9

1.1)

4.9

13.3

I .0

4.7

1.0

1.2

1.2

1. 1

11.7

1.2

19.9

32 .. 8

36 .2

to 02. Tocher et al. ( 1985 l also noticed tluctuations in lipid content/dry \veight of herring.

lan;ac throughout development. especially after hatch in which there cxistt:d a two-fold

increase of %lipid content. This was attributed to the loss of the chorion. the outennost

layer of the l.!g.g which is known to comprise a signiticant portion of the dry· weight in

tlviparous tish. Similar tindings have also been attributed to chorion loss for a lipid

investigation in Atlantic cod. another oviparous !ish species (Fraser ct al. 1988 ).

Although the trt:nd is still appart.!nt within dcvdl)ping redlish dt:spite heing.

ovoviviparous. the percent lipid gain is marginal ( ~9% relative gain) compared with the

100 ° /o gain reported for hcrring.. Likdy this is due to a thinner chorion prcscnt in

developing redtish eggs. Protection from pn.:dators and the physical environment is

provided by the mother in the genus :-;ehasres. and it has been suggested that less encrgy

is ncedcd towards developing a protecti vc chorion ( Bochkrt et al. 1984 ).

From the.: late.: egg stage ( D I) to the latest prc-cxtrudcd stage ( D5 ). there was

nearly a 50% redu~o:tion in total lipid mass from a high initial total lipid concentration 1Jf

- 19 °1o OW. f-raser ct al. ( \988) found a 19 °/o reduction of total lipid in Atlantic cod

\vhcreas rcd drum \vcrc shown to have a 30 °/o loss during devclopmc:nt ( V cttc:r et al.

1983 ). each having an initial concentration of-- 9.9% and 2.4% respectivdy. These data

demonstrate the heavy reliance that developing redtish larvae have on available lipid

reserves. and may indicate lesser usc of other possible energy reserves such as

carbohydrates. free amino acids. protein or glycogen for catabolism.

The increase in phospholipids suggests that this lipid class is not a source of

metabolic energy during egg and larval development of redtish. Phosphatidylcholine

22

(PC). a major phospholipid \Vi thin other cold-v.ater marine tish larvae. is suggested to be

a primary source of energy for developing cod larvae (Fraser et al. 1488: Rainuzzo et al.

199::!). halibut ( Falk-Petersen et al. 1986). and plaice and herring (Tocher et al. 1985 ).

Freshv.atl!r and anandromous tish such as African c•Htish ( Verreth l!t al. 1994) and

Atlantic salmon ( Cowey et al. 1985) havl! also been sho\\n to cataholizt! signiticant

amounts of PC during egg and early larval den:lopml!nt. :\!though individual

phospholipid concentrations were not det~o:m1ined in this study. the im:n:ase in rdativl!

amounts of phospholipid classes through Jevdopmcnt suggests that these lipids \Vere not

primary sources of energy for n:Jtish larvae. Instead. the st~:ady lkcreasc of TAG from

D 1 to 06 mak..:s this I ipid cla::is a more likdy candiJat..: for an l!nergy soun:e.

l"hl.: usc of TAG as an l!ncrgy n:serve during lan;al d~o:\·elopm~.:nt is well

documented (e.g. Cowey d al. 1985: Fraser l.!t al. 1987). hut the degree of TAG

catabolism ,·aries among species. In gl!neral. specil!s with long developmental periods

(e.g. 20 weeks) have higher TAG rl!serves than species with shorter developmental

periods l.!.g. 20 Jays (Sargent 1995 ). No published data an.: availab!t: on gestation times

lor ."i. ml!n!ella or S. fus<.·iutus. but gestation times of other .\'ehastes spp. have been

documcntc:d to he between 1-2 months (Boehlert and Yoklavich \984: Yamada and

Kusakari 1991 ). Highc:r TAG compositions have also bc:en documl!nted in !ish larvae

possessing an oil globule. Redtish larvae have: a discrete oil globule within the:

lipoprotein yolk sac. and it has been shov.-n that these oil globules are rich in neutral

lipids such as sterol/wax esters and TAG (Wiegand 1996 ).

23

The fatty acid composition ofredtish larvae appears to be consistent \Vith other

marine tish species. Docosahcxanoic acid ( DHA-22:6n-3) and eicosapentanoic ;1cid

( EPA-20:5n-3) have long been recognized as important essential fatty acids in larval tish

,.Jevdopmcnt. Both Dl lA and EPA are found in high amounts in phospholipids as well as

the neutral lipids. so they have a dual function in both metabolism and biomc.:mhrane

formmion. Throughout redtish development. Dl 1.-\ and EP:\ k\cls roughly folk)\\ a 2:1

ratio typical of other marin!.! fish species such as Atlantic cod (Fraser et al. I t>X!L Uvlund

et al. 19HX l striped bass (llarrell \995) and :\tlantic herring (Tocher and Sargent \984 ).

lh~ use of L\G ;IS opposed to Pl. classes su~.:h as phosphatidykhuline for

mdabolism is also rellccted in the t'atty acid data. Triacylglycerol is typically higher in

monounsaturates than phospholipids \vhik n-3 PlTAs such as Dl lA and LP:\ an:

generally pmportionally higher in phospholipids ( Wiegard \996 ). B~.nh Dllr\ and EP :\

pcrcentagc.:s of tot;.1l fatty acid are conscned through the developmental stages while it

\vould ;.1ppear that the predominant monounsaturated specics. 18: I n-9 ~md 20:1 n-9. wen~

catabolized. This can be seen in the total monounsaturates as they decrease from .38.2 °'o

in D I to .31.8% in 05 \\hilt: at the saml! time total n-3 PU FAs remain fairly steady at -

32 % through dl.!velopment and may actually be increasing as a percentage of total fatty

acids. Palmitic acid. 16:0. a saturated acid found in high amounts both in TAG as wdl as

the phospholipid class phospharidylcholine (Bell 1989). also increases throughout larval

red!ish development. Thus it would appear that TAG is providing an energetic substrate

for metabolism as well as the essential fatty acids needed for the synthesis of certain

phospholipid classes.

24

Tht: incrcast: in phospholipids throughout larval dt:vdopmcnt ntkn occurs in

marine larvae as phospholipids bccom~ incorporated in the larval body (Tocher t:t al.

1985 ). In a study by Kaitaranta et al. ( 1981 ) the proportion of polar lipids

(phospho! ipids) incn.:ased throughout rot: maturation in Baltic herring ( ( '/upca hurrcngus l

and rainbm" trout (.\'a/mo guirdnl!ri) . :\similar trend is n:portcd tl.)r turbot

(.\'cophtlwlmus maximus) although only t\vo de\dLlpmental periods were compared i.e.

hatch and tirst-ti:eding 1 Rainuzzo et al. 1992 ). Phospholipids an: important components

of biomemhranes and certain classes such as phosphatidylcthanolaminc ( PF) and

phosphatidylscrine ( PS) arc particularly abundant in neural tissues such as the brain and

retina. :\nalysis l)fthese tissues in cod (Tocher and llarvie 1988: Bell and Dick 199 I).

rainbow trout (Bell and TOl:ha 1989: Tocher and Harvie 19X8 ). and herring (lkll and

Dick 1993) have sho\vn these phospholipids classes to he present in high amounts along

with high com:cntrations of DIIA. The amounts of DIIA in these phospholipids ""en:

also shown to increase in the development or h~:rring as rods within thc eye app~.!ared

(Bell and Dick 1993 ). Rc.:dlish eyes grew more than 75% in diameter from D2 to 05

and wt:n: typically grl.!atl.!r than 0.6 mm in diametcr at extrusion. Ratios of eye diameter

to standard kngth of rcdlish larvat: arc calculatt:d to be - I 0.6 1Yo based upon

morphometrk data collected by Penney ( 1987). This is large relative to other North

Atlantic groundtish species such as cod (Gadus morhua) and yellowtail tlounder

( Pll!w·onectes je1-rugnineus) where ratios are 6. 7 %and 6.4 % respectively at hatch

( PU\·anendran unpub. data). Although morphometric data for Atlantic halibut larvae

(Hippog/ossus hippog/ossus) is scarce. eyes of this species at hatch has been

25

char:.H..:tcrized as nonfunctional ( Haug 1990). These data suggest that redtish have high

demands tor phospholipids as structural components in biomembrancs throughout

devdopmcnt. Smaller and perhaps less developed eyes in :\tlantic halibut and cod. on

the other hand. may allow for increased metabolism of structural phospholipids. namely

phosphatidykholine. during embryogenesis in these species.

:\n increase in sterols (S I) is correlated with an im.:n.:ase in hody size and

d~o:\ dopmcntal stage of rcdtish larvae. !"his is not surprising considering the role of ST as

:.1 structural class of lipids. !.ike certain phospholipid classes. STan.: incorporated into

hinmcmhranes and typically correlated with Ian al size and mass (Fraser 19X9 ). :\sa

n:sult ST have been used to account tor size dependency \\hen using lipid content to

evaluate larval condition in marine !ish (e.g. Fraser 19XX. 19X9: llakanson I (.)l)J 1.

Because n.:dtish arc ovoviviparous. caution should he cxen.:iseJ \\hen speculating

into the sources of essential t:my acids during embryogenesis. t rnlike oviparous eggs

which must draw upon a tinitc soun.:e of energy proviJcd during oogenesis.

ovoviviparous larvae may be supplied with additional nutrients from maternal serum

during gestation. Termed matrotrophic viviparity ( Woum1s 1981 ). several ovoviviparous

lish species previously thought to provide no additional embryonic nutrition (i.e.

lecithotrophic viviparity) have recently been found to do otherwise. Among these have

bcl.!n several spl.!cies from the genus .'iehasles ( Boehkrt and Y oklavich 1984: Boehl crt et

al. 1986: Dygert and Gunderson 1991: Macfarlane et al. 199J ). Although continnation

of matrotrophy in redtish is beyond the scope of this study. it is interesting to note that

increased levels of phospholipids have been found in the serum of another Seht.~sres

26

species. S. jlavidus. during gestation (MacFarlane et al. 1993 ). Because these levels of

phospholipids in female serum were higher relative to males during the same period. the

authors suggest that S. jlavidus may be matrotrophic. Therefore. increases in

phospholipids of red !ish larvae during gestation may be the result of maternal

contribution rather than synthesis from yolk reserves.

rwo or the lipid samples used in this study ( I-D3 and 1-D4 stage) \vere collected

from .'i. jl.lsciaws females. but thl!sc data were pooled with samples gathered from .'i.

mentel/u. These two species co-occur and share spawning grounds between April and

July of each year in the North Atlantic. Externally. beaked rcdlish arc nearly identical to

l!ach othl!r although a method using extrinsic gasbladder musculature has been dcvdoped

to distinguish between these species (Ni 1981 ). Larvae of the two species arc also

extremely similar. although subtle diftcrenccs in morphology and pigmentation between

late stage (05) larvae of.\'. memella and S j(lsciutus have been noted (Penney 1985). In

addition to being morphologically similar. the early foraging and swimming behaviour of

the two species of larvae was shown to be identical (See Chapter 3). The integrity of

these two species is thought to be maintained by temporal mismatches in copulation

processes in the fall (St-Pierre and de Lafontaine 1995 ). and the degree of hybridization.

if any. remains unknown. While variation was noted in absolute amounts oftotallipid in

D3. both the high and low outliers were collected from the same species i.e. S. mentella.

It should also be noted that these outliers resulted in little variance~ standard deviations in

lipid class and fatty acid composition rarely exceeded 5% which in tum increases the

reliability of the D I and 05 stages where only onl! sample was analyzed. Therefore.

27

while it's recognized that the statistical pov.;er of a large sample size of both.'.·. mentella

and 5:. fasciatus may allo\V for the qualitative separation of these spccies . ..:ombining both

species in this study should not misrt..!prt:sent overall trends in lipid and fatty acid

..:omposition throughout lan·al de\·elopment.

Tht: variation in amounts of total lipids bct\vcen lanai sampks within D3 is

interesting. l'his may be an indicator of larval dry weight ditTcrences from dift~rent

kmalcs assuming highcr lipid contents are associat..:d with larger larvac for each

dcvdopmental stage. l l nfortunatdy. larval dry \\eights were calculatcd from pr..:scrv..:d

samples of larvac from fcmaks not used in the study. so individual difti.:renccs betwe..:n

sampks could not be determined.

Nevertheless. variation in total lipid rescr.es suggests quality difli.:rences which

could have subs~.:qw:nt effects on lan·al survival alter parturition. Redtish in the North

Atlantic ar~.: noted for their high degre~.: of interannual variability in r~.:cruitmcnt.

t:videnced by changes in lan·al abundance (Anderson !994) and year-class strength (e.g.

Lilly 1987). In fact. int~.:rannual variation is charach:ristic of Sehasles species in the

Pacilic as \veil. suggesting that recruitment mechanisms may be more proximately

intluenced by thc biology of these species rather than the cnvironmt!nt. Support for this is

provided by Moser and Boehlert ( 1991) who purport that qualitative di fferenccs in larvae

could be the result of Sehasles species with embryos that depend on additional supplies of

nutrients during development. They suggest that in years with little food availability for

adult females energy reserves may be conserved rather than used for embryonic

development. This could subsequently result in poor year classes of tish. assuming larvae

28

poorly provisioned in endogenous resources arc more susccptibk to mortality e.g.. due to

starvation and/or size-dependent predation. Although there is substantial variation in

total lipid rescf\es in larval rcdtish. the intluem:e on the survival or d~:~vdopmental ratt.:.

either pre- or post-parturition. remains und~:tennined.

29

CHAPTER3

BEHAVIOUR, GROWTH AND SURVIVAL OF REDFISH LARVAE IN RELATION TO PREY AVAILABILITY

3.1 Introduction:

Fisherie~ biolngists hypothesize that the survival success of marint: !ish is largely

dett:rmined at the larval stage. primarily through the eft\:ets nf starvation (e.g. Cushing

1975) or predation (e.g.. I lunter 1981: Baiky and i loude 1987). These mo components

\)r mortality arc not necessarily exdusive: starved larvae arc considered to be more

vulnerable to predators because redw.:ed growth rates prolong. exposure to size-selectin~

predation (Smith 1985: Gamble and I lay 1989). Successful feeding or tish larvae.

therct(m.!. should increase survival directly by reducing starvation as well as indirectly by

Jecreasing risk to pn:dation.

rhe availability of prd\:rred prey is known to atkct ingestion and growth rates of

larval tish in the laboratory (e.g. Houde and Schckter 1980: Munk and Kii.irboe 1985) as

well as the tidd (Anderson 1994). The temporal overlap of larval tish and their prd\:rred

prey is subsequently thought to affect year class stn~ngth. T enned ·match/mismatch· by

Cushing ( 197'2. 1990 ). the hypothesis assumes that tish spawn at a tixed time along with

seasonal peaks in plankton blooms. Y cars with synchronized release of larvae and prey

("match") should result in higher larval gro\\o1h and survival than unsynchronized years

(·mismatch·).

Redtish tSebastes spp.} are likely sensitive to a match or mismatch in prey

30

bt!caust: they meet the assumptions of the Cushing· s hypoth\.!sis. Larval red fish have a

strong prdcrence for ('a/anus cope pods (Anderson 199-l: Rung\.! and de Lafontaine

1996). a prey species which has been shov.:n to have a variable yearly and seasonal release

(Anderson l <NO). In contrast. redtish spawn intensively for a 1-2 week period in late

.-\pril and early May \Vith little variability between years (Anderson 1984: P..:nny and

Evans !9X5 ).

Although redtish larvae are likely suscl..!ptiblc.: ll) matchl..!s and mismat~.:h..:s of prey

in the spring. thl..! rl..!sponse to thl.!se changes in prey availability is for the most part

unknmvn. In a tidd study hy Anderson ( 199-l ). larval redtish wen: found to he in poorer

condition in a y\.!ar with lower concentrations of pretl!rn:d prey. While tidd studi\.!s arc

valuable in our understanding of lan:al foraging !.!co logy. they are unable to iml.!stigate

the underlying dynamics of foraging bt!haviour. Field studies are also unahk to account

for small-scale prey patchiness and may misrepresent thl..! prey environment by missing

smallt!r plankton in ~.:oarse mesh sampling nets (Frank and Leggett 1986 ).

To date. there have b\.!en no successful atte;:mpts on conducting experiments with

redtish larvae in the laboratory. Likely this is due to the difticulty of acquiring larvae for

t!Xperimentation: redtish are ovoviviparous and are found in deep watt!r (>300m) during

spring spawning (Ni and McKone 1983). Penny and Evans ( 1985) attempted to rear

redtish larvae in the laboratory after collecting ripe female redtish at sea but were unable

to achieve substantial larval growth and survival. In their work. they used Artemia

nauplii. a prey which may have been too large tor the redtish larvae to ingest. Artemia

nauplii at hatch average >400 ~m in length. yet gut content analysis from \Vild caught

31

lan:ae shows rcdtish prefer to feed on prey items -150 ~lm in width. usually in the form

of copcpod eggs (Runge and de Lafontaine \996 ).

Tht!rct(m~. tht! objectives of this study an: to measurt! lar.-al redtish growth.

behaviour. and survival under controlled laboratory conditions. Spccilically. I address the

4uestions nf hmv prey availability (I) intluences growth and survival and ( 2) shapes

patterns of foraging heha\ iour of redlish larvae . The ecological signiticancc of these

tindings is discussed through comparisons with other :\tlantic species.

3.2 Materials and Methods:

3.2.1 Larval Collection

The spawning of beaked redtish . .''it:hastes memella and S. ji.lsL'iulus. overlaps

temporally and spatially otT the ~kwti.)undland coast although .'1. )C.1sl'iaws tends to spawn

later (Anderson 1984 ). The larvae of these two species arc nearly identical to each other

morphologically at extrusion although slight differences in pigmentation patterns appear

to be distinct enough to allow lor separation (Penny 1987).

Adult redtish were collected from bottom trawl surveys aboard a DFO research

vessd off the Newfoundland coast in NAFO area JN. Larvae were extruded from ripe

females into I 0 l plastic containers lillt!d with sea\vater at ambient surface temperature.

A subsample of 10 larval! was removed and measured for total length with digital

calipers. Batches of larvae from females were mixed and transferred to large insulated

holding containers with slight aeration if subsamples were viable (>6.5 mm total length).

Penny and Evans (I 985) estimated tht! total length of redtish larvae at time of extrusion to

average 6.0 to 8.9 mm with some variance between years. A total of tive batches of

.... , _,_

larvae v.·ere gathered in this manner: three were extruded from S. mente/fa !~males and

two from S. fascia/us. Larvae wt:rc kept on hoard lc..>r a maximum of 36 hr bdore bt:ing

transt~rrcd to onshore facilitit:s for experimentation.

3.2.2 Experimental Desig11

LlrYae \\ere stocked at -1 larYac L' 1 in 300 I conical. upwelling containers with

2-4 h illumination (750 lux) and constant slight al!ration. Tanks \\en: provided with

tiltered seawater at a rate of 1 L min- 1• Four prey density treatments \verc set-up: 4500.

1500. 500 and 0 pr<.:y L- 1• Tht.!se prey levds \vere chosen because thl!y ti.:\1 within ranges

found acct.!ptahle ltlr other .\tlantic species rl.!ared in the lahoratory ( Puvanendran and

Brown 199H ). Limited numbers of larvae prevented the 0 prey 1.- 1 treatm~o:nt from h~:ing

replicated. however all other prt:y treatments were conductt:d v. ith two tank replicates.

Temperatures \vere maintained betwt:en I 0-12° l' using h~o:ated sea-\vatc:r provided hy a

counter-currt.!nt t:xchange.

Two strains of the rotili:!r Brw.:himws plicatilis were useJ at JitTerent times during

the 35 d c:xperiment. The smaller strain ( -180 x 1-40 J.lm) was used exclusi vdy t'tlr the

tirst two \VC:I.!ks. with the larger strain ( -300 x 200 J.lm) introduced at a I: I ratio on day

17. Larval.! \Vere switched t:xclusively to the larger strain of roti t~r on day 20 for the

duration ofthc experiment. An even mixtun: ofmicroalgae (.Vannoch/oropsis gadirana

and lsochrysis spp.) was also supplied to containers three times a day.

Rotifer densities were maintained by taking four 5 ml aliquot samples three times

a day (two within 5 em of the surface and two taken in the middle of the water column):

33

prey were adtkd during these times as needed to maintain densities. \kan densities

never tluctuated more than 25 °'o of nominal densities during the experiment.

Standard length ( SL ). myotome height (Mil). presence of prey in the gut and

degree of metamorphosis were measured every live days in a non-lethal manner. Five

tish \vere sampled from e<1ch tank and placed within a beaker of seawater on ice. Larvae

were placed on a petri dish on icc under a stcn:omicmscope with an ocular micrometer.

After measurements the larva was returned to a separate beaker for acclimation \Vithin its

original tank. Periodic observations of rekased lish showt!d this tt) he an eflcetiv..: non­

lethal mt!ans of measuring larval.!.

As larvae mctamorphosc into jmt!nile tish they unJergo a series of morphometric

and physiological changt!s. Tht! degree of metamorphosis was determined hy the amount

of curvature in the notochord in the caudal region ( tlt:xion) as \Veil as the development of

head spines. These measures havc also heen employed hy Anderson ( Jl)94 l as criteria for

determining the degree of metamorphosis of redtish larva~: in the lidd. Larva~: showing

slight curvature of the notochord \Vithout any head spines w~:re consid~:r~:d ··pre-tlexcd:·

The development of head spines and increased tlexion of the notochord classi lied the

larvae as .. llexed."" Othen.vise larvae \.vcre considered ··non-11exed .. if signs of

metamorphosis were not apparent.

Behavioural observations were conducted every sccond day within 1-hr of

adjusting prey densities. Observation pt:riods for ..:ach larva lasted 1-min using the focal

animal technique (Altman 1974) and the order of obsen.·ations within tanks was advanced

each observational day. B~havioural events were categorized into separate Modal Action

34

Patterns (MAPs: BariO\v 1968: Table 3.1) and recorded on a portable keyboard (Tandy

l 02). Five !ish per treatment were observed in this manner before data \\Crc uploaded

and summarized using a bchavioural sothvare pa~kag.e (Observer: Noldus Information

Tc~hnolog.y. Waganingt:n. Netherlands).

1.2.1 Data Anai)'Jis:

:\nalysis of ~0\ ariance (:\NCOV .-\) was used to compare slopes of bd1m ioural

and morphometri~ data vvith age in days as the explanat~H) \ariabk (u = 0.05). :\II data

were tested for normality on Mini tab I 0.2 using histograms of residuals and normal

probability plots. Data whi~h ~ould not med the assumptions of normality were

randomized 5000 times ifp-valucs w~.:re \\ithin 0.10 ofthe set signili~am:e level 0.05

(Manly 1991 ). P-valucs deriv~.:d from the randomization tests w~.:rc th~o:n used to

Jeterminc signiticance. Rehavioural Jata were next pooled into six obsen·ational pt.:riods

which roughly corresponded with weeks: three Jays of obsen·ations comprised one

··v . .-eek"' e.g. week I =days 1-6. week 2 =Jays 7-12.~.:tc. Signiticant Jifli.!rcnc~.:s betw~.:en

trcatm~.:nts at subsc4uent observational p~.:riods wert.: determined using Tukey painvise

comparisons \Vith a family error rate of 0.05 .

B~.:havioural data \.Vere also plott~o:d against mean size {myotome height) taken

within± 2 days of observations. and analysis of variance ( ANOV A) was ~onducted

within 0.05 mm size classes e.g. 0.60-0.64. 0.65-0.69. etc. Signiticant differen~es

betwet!n treatments at these size classes were determined using Tukey painvise

comparisons with a family error rate of0.05.

35

Tabk 3.1: Operational dctinitions of the Modal Action Patterns (MAPs) observed in redtish lal'\ ae.

MAP

Swim

Motionless

Orient

Fixate

Bite

Definition

.-\ quick undulation in the caudal region of the larva resulting in forward movement.

No observable movement ofthe lan·a .

:\head or eye mmemc:nl towards a prey item.

The larva is stationary and bends its caudal region into an ·s · shape position: typically follmvs orient.

The larva 1 ungcs forward from the fixate position in an attc:mpt to ingest a prey itc:m.

36

3.3 Results:

Preliminary obs~rvations of lan.a~ colled~d from females of the two species used

in this study thr.! previous summer showed no differences in foraging behaviour (unpub.

data). :\ny mixing of larvae from S. mentella and .\'. j(JsciaJus \Vas therefore conduded to

have an insigniticant effect on data colkcted during. the experiment.

L.arvat: were obscn.·ed attacking prt..:y items on day I in all prey trl!atmcnts.

Successful feeding was continnl.!d on day 5 during the tirst morphometric sampling

period by the prt:sem;e of prey items in the guts l)f - I 0 ° il nf lan.·ae sampled. Tht:

percentage of larvae with prey items in the gut increased tn-cr time in all prey treatments

until day 25 in which I 00 °/o of the larvae sampled had mtil~rs in the gut. Dift~rcncl.!s in

gut fullness could not be determined without dissecting lan.·ae.

Individual foraging MAPs of orient. tixatc and bite \vcre signiticantly ditkrent

between treatments (Table 3.21. Not surprisingly larvat: in th~.: 0 prey 1: 1 treatment

displayed the least number of foraging MAPs in the three wet..:ks Juring which they \vere

sampled. Foraging activity in the 0 prey l.. 1 treatment was direeted only at piecl.!s of

detritus in the water column. and in no instances were any attempts at ingestion recorded.

Subsequent statistical analyses of bite frequency as well as bit~ ratios to other behavioural

patterns were th~refore conducted indep~ndently of th~ 0 prey L- 1 treatment. It should

also be noted that bite:orient frequencies were calculated only from larvae which

performed 2 or more orients during their observational period. This ensured that larvae

had at least one opportunity to make the decision to bite at a prey item during the I min

observation. Larvae orienting only once may not have had sutlicient time to bite if the

37

Table 3.2: Summary of ANCOVA results on activity and the foraging MAPs of Ia!"\ a~ at varying prey concentrations. ( <~( =0.05)

MAP Source df r p

Sv.-im Frequ~nc~ Covariat~s (day) 2~3.88 <0.000 1 Treatment "' 0.80 0.-NJ )

Error 5:.:!1

:'v1o t ion h.:ss Covariates (day) ') , -_ ,_) 0.13~

Duration Tr~atment "' 8.71 <0.000 I J

Error 5:.:!1

Orit:nt Fn.:quency Covariatt:s (day) .36 .58 <0.000 I Trcatml.!nt "' 11.42 <0.0001 _,

Error 521

Fixate Frt:quency Ct)variatcs (Jay) 1~ . 23 <0.0001 ·rreatmcnt "' 18 .08 <0.000 I .. l

Frror S::!l

Bite Fn:quency* Co-variates (Jay) 27.35 <0 .0001 Treatment ..., 27.:.:!6 <0 .000 I -Error ~l)()

Bite:Orient Covariat~s (day) :.:!3 .78 <0.000 I Ratio* Treatment ..., 21 .08 <0.000 I -

Error ~90

Total Foraging Covariatcs (day) 35 .12 <0.000 I Frequency Trl.!atmcnt 3 16.36 <0 .0001

Error 5:.:!1

* 0 prey L-1 treatment not included in ANCOV A.

38

prey item was enl:ountl.!rl.!d at the end of an obsl.!national period.

By wcl.!k 5. larvae in the -1-500 prey L. 1 tn.:atment oriented signilil:antly more than

lan·ae in 500 prey L"1 (Table 3.3a: Fig. 3.1 a). Signiticantly higher biting frequl.!m:y in

1500 prey L· 1• hmvevcr. \vas recorded in week -l bem·el.!n the -1-500 prey L- 1 treatment and

latl.!r in vvl.!ek 5 betWI.!I.!n the 500 prey L- 1 treatml.!nt (l"abk _:\.3b: Fig. 3.1 b). Ratil'S lll .

bite:oril.!nt showed that lanae in the 1500 prey 1.· 1 treatment wl.!re mul:h more likdy to

strike (bite) after l.!nl:ountering (orient) a prey itl.!m than lar'-=.le in the highest prey

treatment (Tabh.: 3 . .2: Fig. . 3 . .2a). Consequent!~. the degree of total foraging. activity

(MAPs orient. tixate and bitt:) vvas also highest fur larvae in 1500 prey L" 1 (Tables 3.2 and

3.-l : Fig. 3.2b).

Measuring. the time spent swimming was limited by the obsen-er"s retkxcs

because redtish lan·ac have an abrupt swimming. behaviour l:onsisting of short bursts ( <

0 . .2 s). Then.:forc. only the frcquerKy of sv· .. imming I.!VI.!nts l:lluiJ be l:ontiJently analy1.ed.

Occasionally a lan·a would s\vim rapidly for several st.:conJs but this \vas rare. ol:curring

in less than 5% of obsen·ations. Within the tirst 12 days of the experiment. lan·ae rl.!ared

in 0 prey L" 1 swam mon.: frequently (not sign!ticant) than other prey treatments (Fig.

3.3a). After day 12. howcve;:r. larvae in the 0 prey l.- 1 treatment svvam very little anJ spent

signiticant more time remaining motionless (Table 3.5: Fig. 3.3b). The signiticant drop

in motionless duration for larvae in 1500 prey L"1 (Tukey's pairwise comparison <

0.0193) is the result of more time spent foraging. . Swimming. frequency of larvae in the

food treatments did not differ from each other. but all showed similar increased

swimming activity through time.

39

Fig. 3.1 : Foraging fn.:4uency of n.:dtish lana~.: (.'it:hash's ::;pp.) in difl\.:rcnt pre~ concentrations over tim~ : a) orienting frt:4ut:ncy and h) bite frc4uency . b.u.:h wcck is comprised of three days ofohscr.;ations taken cvcry other day . Values arc means lor cach tn.:atmcnt per observational pcriuJ · I SE: n ""' 30 larvae per \Vcck.

40

----e- 0 Prey L-1

7 __. - 500 Prey L-1

A __.____ 1500 Prey L-1

6 - T - 4500 Prey L-1

5

I\ r/t~ >. u c

4 Q) I \ / :::J o- ;/ ~ ~?--Q)

3 lj ~ -. "-LL ) II- ~ ~ ..... c f/ i Q) 2 ·c 0

1

0

4 B

3

>. u c

2 Q) :::J o-Q) I "-

LL Q) 1 ~~ ~

(Q

0

0 1 2 3 4 5 6

Week

41

Fig. 3.2 : Foraging fre4LI\:m:y ofredlish larvae (.','ehaslL!,. spp.) in difkn:nt pr~y ~on~~ntrations over time: a) bit~:orient ratios expr~sst:d as a p~n.:cntag~..: and b) total foraging fr~4u~n~y (ori~..:nt +- tixatl.! + hit~) . La~h \\eek is ~omprised of three days L)f observations taken every other day. Valu~s arc means lor l.!ach tn:atment per observational p~..:riod · I SE: n ·-= 30 larvae per w~~k.

42

0.55

.- 0.45 ;;:R 0 .....__...

0 +=i 0.35 ro a:: .... c Q)

0.25 ·c 0 Qj ~

co 0.15

0.05

14

>. 12 u c Q) 10 ::J CT Q) "'-- 8 u.. C) c

6 C) ro "'--0

4 u.. ro ....

2 0 1--

0

A

0 1 2 3 4

Week

43

5

_._ 0 Prey L-1

--- - 500 Prey L-1

--A- 1500 Prey L-1

- T - 4500 Prey L-1

Fig. 3.3 : a) Swim fn.:4ut:ncy and h) tim~ spent motionkss of redlish larvat: (,'-,'uhastt!s

spp.) over time. Each week is comprised of three Jays uf observations taken every other Jay. Values arc means for each tn.:mmcnt per observational period · I SL n = .30 larvae per \\:eck.

44

45

Tabl~ 3.3: Tuk!.!y·s pairwis~ ~.:omparison of (a) ori~nt fr~4u~ncy and ( hl hit~ fn:4uency in larval r~dtish. Signitkant dift\:n:nc~s o~.:cur whi.!n.: 0 li~:s tlutsidi.! th~ rang~ tlf list!.!d contid~:n~o:~ int~:rvals of ~ach tl.!st. *Signiticant ditkrenc\.! ( p < family aror rate of 0.05 l.

aw\.!~ks 1-5 ar~ ~.:ompriscd of three observational pt:riods tak~nov~r a six day period. w~~k 6 is comprist:d of two observations tak~n over a live day period.

46

A Week a 0-500 0-1500 0-4500 500-1500 500-4500 1500-4500

l -2.-l.!X ll.lhl -:! .lJ:!X -o .:B•J• -2 .7(11 -0. 172• -1.557 Oj57 - I .No 11. 7::! -1 -O.!NO 1.22-1

2 -3 .5-W 2.122 --tx07 11.1!55 -5 .-W? 0.255 -U-ti O.X07 -3'141 0.207 -::! .h74 1.47-l

3 - -U~-17 0.113 -5 .2-17 -0 2X7• I --l .IJ l.l o on - I X.~2 1.11.12 -I.-1'J'J I jhS ·I .O'J'J 1.7h5

) -l ------ .... ..... .... ....... .... .. .............

I ............. ------ -2.45-1 1.021 -2.21\7 I.IX 7 -UX7 I .T21

5 ------ ------ ---·-- ......... .. .. I ------ .. ........ .. -2 .X2h 0.55'J -.1554 -0.07o• -2.-l:!O 1.057

6 ------ -----· ------ ------ ------ ------ I-4 .X02 -1.2tl4. -.l XXX -tUo:i• -O .XOX :! .flXI

Week a 500-1500 500-4500 1500-4500

I -0.39-lX ll.32M2 -O . ..J2X2 0.2•J..JM -O .. N..JX 1U2X2

2 -l.-l5'J () :! 5'J - I...J .W 0.25•J -O .X:i'J O.liW

] - 1.0132 o.079X -O.X79X 1121.42 lUI]:! o o7•JX

.., -2 . ..J5J 11.111!7 -0 I)X 7 1.5:U OJj I 2.110.\•

5 -2. 7X7 -o.xu• -0.710 IJ17 1.0'10 3. 11 7•

II -3.1 ')tJ -I . ..J:!tJ• -O.X75 O.'Jio 1.-I:W .L~o-t•

Table.: 3.-l. Tukcy·s pairwise comparisons of bite frc4ucnl:y in lanai r~..:Jtish. Signiti~ant

JitTcr~..:nccs occur wh~r~.: 0 lies uutsiJ~.: th~..: rang~..: of list~..:d l:ontiJence intervals of ~..:ach test. *Sig.ni tic am Ji ffer~..:nc~..: ( p < family crror rate of 0.05)

•1Wedi.s 1-5 an: comprisc.:J of three.: obsc.:rvational periods tak~..:n ov~..:r a six Jay

pc.:riod. W~..:ck 6 is comprised of two obsc.:rvations taken ov~..:r a live.: Jay pl!rioJ.

48

: . ,. . Q <: .. ! ..... ;::: ....... -c ~ . ~ ;;:_ ~ X ,.., =-~. "'T •r: =-..,. .... , ~ . ..c ....... =-I

~ I '"'' ~. r-- •r. ~. .c ;::: ?;: •r. ~ i •r, .c

....: or, "'T

I - : I -- --- ---I

I . ~ I

....... '"'' ~. --. '::: '.:: x ~. = "'I "'T rl

; I r - =- ~- .c X "'T l/j l X: r1 f= <;:: .......

I -c ,., ...... ....... : '';·

I .. . ....... .c f'l =-g) X

~ ....... ;<:: ;:-, '::: ("·, l/j '':": -I Q

X = tr, .,., =- ~ .c

~ ....... :::-

~ ;2 =-•r. X

"'"!' '7 '";'· -9 =1

='

. . ;. X

X =- ...,. ,~. = = l/j ..,.

I •r.

= "'T' ~. <'I f'l X _,. "7 - =1

; . <'I

_,. •r. .......

g X .c ...,.

'";'· ~ ' .,., -I = -c •r, ...,. :c ....... rl

~ =: ~-

• ...,. X ...,.

-c r; ~ Q :-i ..-. ~ = tn I = r=:: X .c ...,. <'I

""'! .c :::-. '':' -4 r;:

<"I r-,

49

Tahk 3.5. Tuk~.:y·s pairwis~.: comparisons of tim~.: spent motionless in larval redlish. Signili~ant Jifli:rt:nees oe~ur \vh~.:re 0 lies outsiJ~.: the range L>f listed conliJen~e intervals of each test. *Signitic.mt difli:rcnce (p < family error rate of0.05)

aweeks 1-5 are comprised ofthr~.:e ohs~.:rvational p~.:riods taken on:r a six da:y period. Week 6 is comprised of t\.VL) ohservations taken L)Vt:r a live Jay period.

50

! . e l :f -C •r. •r.

X: ~ = ~. =- r"'l ':::: ~ :-!"'I tr;

~ X: ...-: = ; ..,. I ~

~ I f""l :!

- I ~ ;:::: r"'l ~ .-. ~. =- ..... t"l f""l I" I ,-j

l ..... ,.., ; r;: r;:

!

.r. .r. ,.._ X: ~ as ,.., ~ .c. ,_ ..,. f""l •r . ..,. •r. -C ~ ..,.. r""l ..,.

~ 17. ,:; r-- =-=- I" I =-•r. ""· r1 =- -'';· '':: ;

• •r. - ~ x ...... ~ - I" I <"' I - =- ..... X: X: ..... 17. ~ f"l •r. ..,.. •r. -I = = f:. ~ tr; x f"l .r. ~ ,..I .... X f"l :c ; I" I .... I ~

x •r, ~ X:

rl -. = r-- ..,.. ~ X tr; ..,.

I e r-- I" I -C x •r . ... , X:

...... •r. ~ X ~ -. r--= = X

Ill -I = r-- ~ t"l ..,. ~ •r,

X ..... ...,. '"';'·

.-. •r. ~ ,c X: X: r"'l ...... = ,c -.,.; -= lr,

I = r-- ...... <"'I =- =- •r. <'I ...,.

"":'; "i t""",i

" ~ ~ ~

~ r -1 ~ "T tr) ..0

51

Growth and condition of laf\·ae was dependent on prey concent;-:1tion. Laf\·al S L

varied between treatments over time (Table 3.6 ). and larvae in the 1500 prey L-1 treatment

\vere sig.niticantly larger than laf\·ae in 500 prey L- 1 and -1-500 prey L- 1 hy the end of the

experiment (Table J.7a: Fig. 3Aa). Myotomt: height (MH) \Vas also sig.niticantly

difll:rent between treatments (fable 3.6). but ditTerences nccurn.:d t:arlier than SL for

lanat: in the 1500 prey 1.' 1 treatment (Table 3.7h: Fig. JAb). The larvae in 1500 prey 1.' 1

shmved highest o\·erall mean growth at 0.07-l mm SL .,.r 1 compared to -t-500 prey L' 1 and

500 prey L' 1 at 0.055 and 0.05-l mm SL d' 1 respectively (Fig. 3.5a). Larval conJition

incn.:ased as a function or age in all treatm~:nts (fabk 3.6 ). but larvae had best ov~:rull

condition at the t:nd of the I.!Xperimt:nt in 1500 prt:y L-1 (I'abl...: 3.8: Fig . .3 .5b).

Because growth rates vaned between trl.!<.llm~..:nts. behavioural measur~..:ments wen.:

plotted as a function of siz~: ( MH) indep~:nd...:nt of age. Myotome h...:ig.ht was used in plac~:

of standard length (SL) because it app...:ared to be kss a!Tected by morphological chang...:s

associated \Vith m...:tamorphosis e.g. post~..:rior notochord llexion. Mean ori...:nt frequenc)

as a function of size (Fig. 3.6a) indicates that prey encounter rates in the middle and high

prey treatments arc higher than the low prey treatment. However. significant di fkrenct.:s

did not occur until the largt:st size class (0.60-0.65 mm) (Tukcy"s paif\vise comparison <

0.0193 ). Intluences of size on mean total foraging (Fig. 3.6b) shows a similar trend as

plots against age (Fig. 3.2b). Similar sized larvae appear to be foraging at different rates

between treatments as they approach 0.6 mm. This is shown statistically between the

1500 and 500 prey L' 1 treatment <Tukey's pairv~ise comparison< 0.0193) but not between

1500 and 4500 prey L'1 (Tukey's pair.vise comparison> 0.0193) at the 0.60-0.65 mm size

52

hg.. 3.4 : a) StanJard kng.th (SL: mm) anJ b) myotome height (~·HI: mm) of larval reJtish (.'iehas/es spp. ) subjt.:ch:LI to prey concentrations of 0. 500. 1500 anJ -1-500 prey 1.· 1

•

Valut.:s an: means (n = 10) · I SE.

53

-E E -.c. -a. (1)

0 >. "0 0 Cil

11 l A I I I

I

10 _ j

9 -:

8 _j

I

7 j

18 I

1.0 I

l I I

0 .9 -j I I

o.a I I

I 0.7 ·-[

·r '

.L

0 5 10 15 20 25 30 35

Age (days)

54

-e- 0 Prey L_,

-II - 500 Prey L_, ____.__ 1500 Prey L_ ,

-~ - 4500 Prey L_,

Fig. 3 . .5 : a) Growth ratl.!s (mm Sl. J' 1) and b) condition indl.!x · I SE (~tll/SL) l)f larval

rl.!\.itish (.)'ehasres spp.) subjl.!ctl.!d to pr~.!y con~-:1-!ntrations of 0. 500. 1500 and 4500 pn:~ 1.' 1

• Values an: means (n= \0).

55

0.20 iA - i

·~ 0.15 ~ "0 .....J (j)

E E Q) .....

l 0.10 ~

I

~ 0.05 -j i ..r::. .....

~ i e o.oo _j (9 c rn ' ~ -0 .05 :

I

IB 0.100 "l

i 0.095 l

I ... ( !

I

X 0.090 -~ I i_

~ 0.085 ~ i ~· j /1 j

~ 0.080 II v ~/ ~ t:0

0.075 l A --I !P: v ~ ;/~/ (.) 0.070 1 ~ /~

o.o65 ~ '-~~=._f:::t~r

--- 0 Prey L-1

_. - 500 Prey L-1

-~ 1500 Prey L- 1

--y- 4500 Prey L-1

0.060~ ~ 0. 055 ----"-1 -.---,----,--.----.-~--,-----.--__j

0 5 1 0 15 20 25 30 35

Age (days)

56

Fig 3.6: a) Ori~nt fn:4uency anJ h) total for:.1ging fn.:4uen~:y ofredlish l:.uvue (.\'chaslt.!S spp.) in prt!y .;nncentratinns of 0. 500. 1500 anJ -+500 prey l.- 1 as a function of lar\'al size (myotom~ h~ightl. \tyotome height valul.!s are ml.!uns (n-= 10) takl.!n 1.!\ery live days and behavioural valul.!s are ml.!ans taken± 2 Jays of size values ( n=20-30).

57

• 0 Prey L- 1

• 500 Prey L-1

~ 1500 Prey L-1

7 ... 4500 Prey L.1

T

i r---•t-----11 I

I I

I

• .......

0 J !

12 J -;-

i + I I

0> 10 ~ T I ~~

c I I

aJ ~ r-L .L

l ·a, ro '-0 I 1 ,

I u_

6 _ _! T r-T .l ~

ro I ...... ! i~t I 0 i ~

I I

c 4 -J ~ I

t-4--1 i ro _L I Q)

2 i+_._- I ~ l l_

I

0 l I I • I

0.4 0.5 0.6 0.7 0.8

Size (myotome height)

58

Table 3.6: Summary of ANCOVA results for morphometric and ~ondition changes for larvae at varying prey concentrations. ( o=0.05)

Morphometric Source df F p

Standard Length Cov<1ri<1tes (day) J0'-)4.37 <0.000 I (SU Treatment

., 13.08 <0.0001 _l

Error 293

~lyutome I kight CGvariates (Jay) 5-H>.53 <0.000 I (\I II) Treatment 3 15.08 <0.000 I

Error 293

(\mJitiun C nvariatc.:s (Jay) 2H I.X8 <0.000 I ( \tii;Sl.) rrc.:atmc.:nt

., 13.66 <0.000 I .)

Error 293

59

rabk 3.7: Tuk~y·s pairwis~ ~omparisons nf(u) standard l~ngth (Sl) and (h) myotom~.! h~.! ig.ht ll'vlll) ml.!asur~.:J ut li \'\! Jay i nt\!rvals. S igni li~ant JiiT~r~.:n~.:~s occur wht:r~ 0 i il.!s outsid\.! th\.! rangt: of list~J ~ontidt:nct: intt:rvals of ~ach t~st. *Signilicant Ji!Tt:rt:ncc ( p < family error rat~ of0.05)

60

I I ...... ... ,

~I - , ~I

..,. ... , •r.

...... ..,.

..... :=:

.... , ~

~~~----------------~

Q Q ll'l -I Q

Q Q ll'l

I Q

.... , :=:

,.., ....

X ..,. ,..,

.c ..,. ,,.,

,,..,

. •r. ~ ......

X: X:

,,..., I"' I ...... .::

-:;­... , ,,...,

I

... , .c

~

" ...... •r. ,...,

~

or, ......

,,..,

~

~

~

.,., t"l

:=:

X: ..,.

.,..., ....,

61

.. ,...., ~

:=:

,..., <:!

. ...... '!:.:

,..,

:=:

--· ;:­,..,

..,.

......

X:

s

:=:

I"' I

I~

" ..,. X

:=:

~-~--------------------··---

-Q ll'l -I Q Q ll'l

:=:

•r, ':!

. ~·

,...., ...... :=:

~

..,. §

f-· 1---.. ·-·--·---·--------------

--~ ..., =

Q Q ll'l -I Q

. £

.... '

,,.,

.. ::c §

X: •r,

..,. X:

...... ..,.

.,..., .,., t"l

,,.., ~

Table 3.8: Tukey·s pairwise l:umparisons of larvall:ondition measun:J at live Jay intervals . Signitil:ant Jifkrenl:es l)l:l:Ur where 0 lies outside the range of listed confiderKe intervals of each test. *Signilicant Jiftt!rence (p < family error rate of0.05)

62

63

range. Bite :orient frequc:ncies bet\veen larvae in the 500 and 1500 prey L" 1 treatments

were not signiticantly different at the largest size class (0.60-0.65 mm) (fukey·s pairwise

comparison > 0.0193) (Fig. 3.7) but \Vere signilicantly lower for larvae in 4500 prey L- 1

than 1500 prey L- 1 in this size class (Tukey·s painvise comparison > 0.0193).

Increased growth rates in the 1500 prey l." 1 treatment com:spondl.!d with increased

larval survi\al and dc\dopmcntal rates. Although somc larvac livcd to da~ I 8 in the 0

prey L- 1 treatment. 50 n,;, monality occurred hy day 5. Su. vivalof Ian ac in fllod

treatmcnts was otherwise dcp!.!ndent upon prey CL)nccntration. Ry the cnd of thc

experiment. larvae in the 1500 prey L- 1 treatment had the highest survival at 26 '' 'u

when:as both thc 500 prey 1.· 1 and -+500 prey 1." 1 treatment had lowcr survival at - 7 '1'u

(rig. 3.8a) . or thcse survivors. - 90 °'o of the larvae samplcd showed signs of tlcxion in

1500 prey 1.- 1 compared to -50'% of lan.·al.! in both the 500 and 4500 prey l." 1 tr~:atments

(Fig. 3.8b). Whilc no lal"\·ae in thc 500 and -+500 prey l." 1 trl.!atmcnts werc dassilicd past

a prc-tkxion statc ofmctamorphosis. 78% ofth~: larval.! in thl.! 1500 prey 1." 1 trl.!atment

sht)Wed signs of full tlexion.

3.-4 Discussion:

With the exception of the 0 prey L.- 1 treatment. larvae fed. grew. survived and

initiated metamorphosis in all the prey treatments in the study. Larvae t't!d at 1500 prey

L- 1• however. had the highest overall survival. condition. and growth at the end of the

experiment. Because optimal foraging conditions can be int1uenced by a numbt:r of

factors such as stocking density (Houde 1975. 1977). light levels ( Puvanendran and

Brown 1998). turbidity (Grecay and Targett 1996). and turbulence (Sundby and Fossum

64

• 500 Prey L., • 1500 Prey L., ~ 4500 Prey L_,

0 .6~·

-0.5 --'

I

.. --1 !

.L -c - ~ 0.3 -; 0 Q) -co ~ 0.2 Q)

~ I I I

0 .1 i 0.4 0.5 0.6 0.7 0.8

Myotome Height

Fig. 3. 7: Mean bite:orient frequency of larval redtish subjected to prey concentrations of500. 1500 and 4500 prey L-1 as a function of mean larval size (myotome height). Myotome height values are means (n= l 0) taken every 5 days and behavioural values are means taken within 2 days of size values (n=20-30).

65

Fig 3.8: al 1\:n.:~.:nt survi\'al and h) m~:tamorphosis nl"redlish larvae (.'ieha.wes spp.) in pr~:y conc~:ntrations of 500. 150() and -l500 prey L- 1 at day 35 . Nktam,>rphosis valm:s arc t:xpress~:d as a pcn:l.!ntagc of larvae showing signs of either prc-tkxion or lkxion. Sun ivai is the average ,>f twu rl.!plicah.:s : I SE.

66

rn

0 .35 ·~--------------______, A

i

0.30 ~ j

i 0.25 '

i

·~ 0.20 ~

(f)

~ 0.15 -i 0

c: .Q X <D

i+= I

<D '-0. -c: 0 ·x <D

u.. ~ 0

0.10 ~

0.05 l

IB 1.0 l

I I

0.8 l

0.6 ~ 04 ~

0.2 ~ l I

I

.-----,

I

0. 0 _.___...J......___---l..,.l _.~___ _ __j_--l __ __L____;

500 1500 4500

Prey Density (prey L-1)

67

-Survival

~ Pre-flexion i I Flexion

\990). this result should be considered as a· starting point" to\vards und~:rstanding the

early foraging ccolog) of rcdtish lan ae.

Attack and consumption rates of tish larvae arc typically asymptotic \\hen using a

range of prey densities in the laboratory (Houde and Schckter 1980 ). Subsequent survival

and growth also tiJI\ow a similar curve at higher prey densities until an asymptote is

reached (Werner and Blaxter I 980). lh~: signilicant reduction in gmwth and survi\·al at

-+500 pn:~ L·' in this exp~.:riment. therefore. was unexpected. Two s~:parate hypotheses

may explain this result for the high prey treatm~.:nt : I) water quality or 2) a confusion

eft~ct.

lm:reased rekase of metabolites hy .·lrtemia nauplii at high densities in the lab

( > 8000 prey 1.·1) has been suggested as being detrimental ti.)r lish larva~: ( lloude 1975 ).

Atlantic end have been shown to have reduced survival at high densities (>8000 prey 1." 1)

( Puvancndran and Brown submitted) as have other species of marine tish larvae (sec

Leger et al. \986 for review). /Jrw:hionus sp .. how~.:n:r. have not been reported to n.:duc~.:

\Vater quality in the same manner. and these prey al densities > -+500 prey 1:' in our lab

with other tish species have not been shmvn to be detrimental (Gotccitas et al. 1996).

Lastly. tlow rates set at I L min·' exchanged- 5 tank volumes of watt:r pt:r day. so it is

unlikdy that poor water quality contributeu to reduced larval gro\vlh and survival in the

high prey treatment.

The second hypothesis (i.e. a confusion dtect) is evidenced by patterns in the

foraging behaviour data. Mean total foraging frequency was significantly higher in the

1500 prey L" 1 treatment than the 4500 prey L- 1 treatment by week 5. Equal frequencies of

68

orienting behaviour. however. existed for larvae in the 1500 and -l-500 prey L. 1 treatmcnt

throughout thc entire experiment. Accounting for grmvth diffcrenccs. larvae in the high

prey treatment arc actually cncountcring more prey at a gi\·en size than larvae;: in lm\er

prey dcnsities. The bite :orient data. ho\.vevcr. show that larval foraging dticicncics in the

high prey treatment \vert: markedly· lmver than larval.! at 1500 pr~:y L- 1 as \vdl as 500 prey

L- 1 \vhen accounting for size differences. The low ratio tor larvae in the -l-500 prey L-1

treatment indicates that these larvae \vere orienting - 10 tim~:s fiJr every hite within the

0.60-0.65 mm sizl.! dass. In contrast. larvae in the low and high densities arc - 3 times

mort.! cfticicnt at this sizl.! i.e. oril.!tlting - 3 timl.!s per hitl.!. It would appear that Ian ae

wen.: re-orienting as morl.! prl.!y items entered their tidd of vision. Rl.!dtish toraging

routines (orient. lixate and hite) soml..!times lasted more than 6 sec in smaller larvae. and it

\Vas often noted in the high prey tr~:atmcnt that larvae restarted thcir foraging routine

\.vhcn anothcr prey item s\\am past their tidJ of vision.

It is intcn:sting to note that this confusion effect in the high prcy treatment appears

to become more pronoum:ed with larval maturity. This may be cxplaincd hy

dcvelopmental changes occurring within the eye resulting in greater perccptual ticlds tor

tish larvae. In general. perccptual distance and angle incrcase both with increasing size of

tish and prey (Hunter 1981 ). As the larY:-II tish grows it has to discriminate among more

stimuli within its perceptual range. Hairston et al. ( 1982) suggcsted that higher amounts

of prey detected from increased visual tidds should lead to higher feeding rates in

planktivorous tish. Under initially high prey densities. hmvever. redtish larvae would

appear to contradict this theory: increased encounter rates from larger visual tields

69

resulted in fewer attacks toward prey and proved detrimental in tem1s of larval grO\vth

and survival.

Three-spined sticklebacks have been shown to be confused \Vhen L)tTen:d Daphnia

sp. at high densities in the bboratory {Milinski 1977: Heller and ~lilinski 1979). In these

studies tish prekrred to forage only at higher densities when at hungrier states because

they had higher ·attack n:adincss·. With increased satiation. tish \vcrc able tL) forage

much mon: efticit:ntly (had highi..!r capture succt:ss) in lower densities than higher

densities. !Idler and Milinski ( 1979) suggest that there is an increased predation risk

when feeding in hig.ht:r prt:y densities: more concentration is needed to ovcrcome

confusion and less time can be dev·oted towards predator vigilance.

Redlish larvae forage in th!..!ir environment by repositioning. themsdves through

abrupt swimming .novcments and then pausing to search for prey . Tcrrned ·saltatory

search" {()"Brien et al. ! 989). this foraging strategy has bct:n described in a numbcr Llf

larvae lish species including. white crappie (!'omoxis annularis: Brov.man and o· Brien

1992a). golden shiner (.Votemigonus o:r.mleuc:as: Browman and O"Brien 1992b) and

Atlantic cod (Gadus nwrhua: Puvanendran et al. submiltt:d). Svvimming fn:4uency in tht:

0 prey L" 1 treatment would be predicted to be highest assuming. search time.: increases with

lower prey availability. This has been demonstrated in larval cod (Munk 1995) and

Atlantic herring. ( Munk and Kiorboe 1985 ). Although swimming. frequency in the present

study was higher in the 0 prey L- 1 treatment during week 1 and 2. it was not signiticant.

By week 3. however. larvae at 0 prey L" 1 swam signiticantly less than other prey

treatments. A critical period or ·point-of-no-return· ( PNR) has been described tor marine

70

larvae shortly a tier yolk rest:rves are depleted and exogenous t~eding must ensue ( Blaxter

and Hempel 1963 ). This period is typified by high mortality. sluggish swimming and

gt:neral inactivity so it is possible that n..:dtish undl..!rwent such a critical pl..!riod shortly

atkr day I 0. Although highest mortality in this experiment was L)bSt.:I"\1-.!d in the tirst fc\v

days. it is probably not an ;.H.:curate retkction of li.lod availability as yolk-sacs \\cre not

l)bscrvl..!d to bl..! cxhausted until day· tivl..!. Initial mortality in this I..!Xpaiment is mon.: likdy

due to handling stress in the transkr from thl..! n.:search ·.-essd to lab aljuaria.

Furthcr evidence fur a critical period is provided in the gru\\th rate data.

Estimatcs t)f growth rates ti.)r lanai rcdtish can vary both intra- and intcrannually.

depending upon a\ailability of pn.:ti.:rrcd prey typl..!s (Anderson 199.+). changes in seasonal

heating cycles (Anderson 19H-+) and cohort strength (Penny and Evans 1985 ). The

highest avaage growth ratl..! achicvl.!d in our l..!xpcriment was 0.07-+ mm SL o· 1 by larvae in

the 1500 prey L" 1 trcatml..!nt. Anderson ( 198-+) rcports ml..!an grov•th rates of larval redtish

averaging 0.136 mm SL d" 1 in 1981 using a length fre4uency methuJ. Pt:nny anJ Evans

( 1985) report lower estimat<:s of 0.109 mm d' 1 for the same larval sampks by correlating

daily otolith incn..:m<:nt with total length. Thl.!se studies. however. have consistl.!ntly sho\vn

larval redtish to have relativdy low or dcdining growth rates within the tirst two weeks

of devdopment. Mean gro\\'th rates of larvae in all treatments in our experiment also

declined initially with the.! lowest growth rates being tound in the 0 prey L- 1 treatment.

Anderson ( 1984) reports increased mortality during this same period of reduced growth.

strongly suggesting a critical pc.!riod during this time if mortalities are indeed growth

rel~;.;d. Untortunately. day to day mortality data is not available tor the prey treatments

71

to compare w·ith the mean gro\\lh rates. but it would be reasonabk to expect higher

mortalities bet\veen days 5 and 20 when growth rates were lowt:st.

The noticeable drop in foraging acti\ ity Juring week 3 may be the n:sult of weak

larvae at the end of their critical period. Orient. tixate and bitl.! fn.:4uency increasl.!d in all

treatments from Wt!t!k I to \WI.!k 2. rl)lloweJ by a notict!abk Jl.!dinl.! Juring \\Cek 3. anJ

then rehoumh:d during we~.:k -+ . rhc Jcclin~.: could han: b~.:en du~.: to reduced I(Jraging

activity from Wl.!ak lan·at: Juring this period of time. The :-;imilar response across

treatments f{lr all foraging behaviour suggests that treatment dfects w~.:re not responsible

for the trend.

Comparisons of these results tl) those found in th~.: tidd with n:dlish larvae.

howen:r. should be exl.!rcised with caution. The enriched rotit~rs used in this experiment

likdy have a difkr~.:nt nutritional valut! compan.:d "•ith pn.:krn:d wild .tooplankton.

namely ( 'alanustinmarchicus. R~.:aring mi.lrine larva~.: in the laboratory also oli.en

n.:4uin:s using pr~:y dt:nsities higher than thost: typi~.:ally r~:ported in the tidd. To date. no

experiments have suc~.:essfully taken larvae from lirst-ll:eding to metamorphosis using

prey levds reported from tield studies. Either tidd estimates are not st:nsitivt! to pat~.:hy

prey distributions or laboratory rearing conditions do not dosdy simulate tidd conditions

(MacKenzie et al. 1990). Increased turbulence has been shown to increase encounter

rat~:s of larval cod over calm water conditions in the lab (MacKenzie and Ki0rboe 1995)

and tield studies have shown teeding rates to be higher for larval tish in mort: turbulent

environments (Sundby and Fossum 1990). Turbulence is theorized to function by

increasing predator-prey encounter rates (Rothschild and Osborn 1988: for other views

72

see Browman 1996). but '.Ve were abk to accomplish this in our experiment by increasing

prey lknsities.

Tht! ecological signi ticance of this study can best he understood by comparing

redlish larvae \.Vith other marine !ish larvae observed under similar conditions .. -\tlantic

cod larvae an: ideal candidates as they overlap temporally and spatially with redtish

larvae during spring spawning otT the coust of Greenland (Bainbridge und ~kKay \968 ).

Fkmish Cap (Anderson and :\ken head \981: Anderson \982) and to u smaller extent on

()corges Bank ( Shem1an et al. 1981 ). !3oth larvae show a prcl~n:ncc tor ('a/anus

copepods Juring early development. but cod larvae hav..: been shown to switch to a more

div..:rse dil.!t earli~:r than redtish larvae (Bainbridge and McKay \968). This diet S\\itch is

likely du~: to th~: much higher grmvth rates reported tor coli than redtish. CoJ gn)\vth

rat~:s in the laboratory an~ n.:portcd to be 0.20 mm SL ,.r 1 for the lirst 30 days of

devdopment ( Puvancndran and Brmvn suhmith:d ). nearly thre~: times faster than

maximum r~:dlish growth rates achieved in our experiment. As a consequence. laboratory

reared cod larvae require high prey densities ( -4000 prey L- 1) and do not survive below

1000 prey L- 1 v.· h~:n reared with Brac:hionus sp. ( Puvancndran and Brown submitted).

Older and larger cod larvae seem more tolerant of lower prey densities ( Munk 1995 ). but

this is a typical phenomenon tor tish larvae as they grow and develop better vision and

digestive capabilities (Noakes and Godin 1988) while swimming ability increases (e.g.

Rosenthal and Hempel 1971: Laurence 1972).

It is therefore possible that low prey availability is less limiting for redtish than it

is tor cod in the tiel d. Anderson ( 1994) found that gro\\-1h and survival of redtish larvae

73

,..-as better in a year when overall pr..:y abundance \Vas lower than the follmving year. He

conduded that qualitative aspects of zooplankton such as size and type may be more

limiting to survival than prey quantity. Cod larvae on the other hand are likely more

sensitive to a mismatch in prey abundance than redtish lar.·ae. Evidence that end are

susceptible.: to mismatches in prey availability exists from both studies in the laboratory

1 Gotccitas c.:t al. \996) and the ticld (Cushing 1990 ). The ruk of prey quality ll!1 growth

and sun· ivai of this species remains pl)or\y understood. but it is reasonable to speculate

that the more diverse diet of cod larvae increases tokrance tn 1 ears when prey types are

more varied. The ditTcrent prey requirements of redtish ;1nd cod may be a means by

which these tWl) species avoid resource competition during the spring spawning season

when they often co-occur in high numbc.:rs.

74

CHAPTER4

SUMMARY AND FUTURE RESEARCH

Variability in ~ndog~.:nous n:soun.:cs as wt:\1 as behaviour. growth and survival in

accordanc~.: \Vith 1-!xogcnous r~sourc~s suggc:sts that recruitmc:nt prncc:ss~s in rc:dtish

pott!ntially start at an ~arly ~tagc. Recruitment processes may indudc: 1-!ithc:r direct

starvation or incn:asl.!d predation at vulnerable: sizes as a results of dc:~.:reased growth

rates. Atlantic rc:dtish n:quin.:mc:nts for ~ndogl.!nous and c:xogc:nous rcSl)Un.:c:s during

early larval dc:velopment. hmvc:vc:r. have only bel.!n partially described in this thc:sis.

Sevc:ral arc:as in this early lit\: history should he explon:d to both gain further insight into

th~.! resiliency of matches and mismatchc:s in prey as wdl as understand the c:vulutionary

success of these sp~.!cies.

Lipid and fatty acid pro Iiles of eggs prior to the l ' 1 devdopmc:ntal stage described

would he usdul f'(lr comparisons with other oviparous tdt:osts. Biochc:mical information

l1!1 non-oviparous marine tekosts is limited making it difticult to compare lipid/ fatty acid

changes of .")l!hasles spp. \vith other tish species because dt:vdoping sequl.!nccs arc not

analogous. Developing egg sc:qucnccs of .~iehasles spp .. despite being t\:rtilized. \vould be:

more comparable to developing oviparous eggs from other marine teleosts . Detailed

stage descriptions of Sehawes spp. egg sequt:nces would have to be ~.:onstructed a priori.

however. since egg age cannot rdiably be used in internal developers.

The metabolism of yolk and oil globule after parturition would also help

determine critical periods for tirst-feeding in redtish larvae. Larvae began feeding prior

75

to day 5. shortly after yolk sacs \vere exhausted. However. some larvae were able to live

well past this point to day 18 despite having no prey available. Whitt: this may be the

result ofmetabolising alternative energy reserves {e.g. muscle or phospholipid). a more

likely source of energy was thl.! oil globule. Typically oil globuks are rich in neutral

lipids such as TAG. and these lipid reserves arc otkn consumed later in lkvclopment

than yolk reserves (Wiegand 19(.)6). Then:forc. it would be interesting to investigate both

the metabolism of lipid reserves attcr extrusion as well as the partitioning of these

resoun:cs bet\vccn yolk and oil globuk.

Qualitatin: aspects of prey (e.g. size or nutritional content) would he an important

area for further study . As shmvn in the feeding c.!Xpl.!rimcnt. pn:y lknsity rcquireml!nts for

redtish larvae arc considaably lov,:er than thl!y arc for :\tlantic cmllarYac. rhis may

imply that larval redlish arc less sensitive to mismatches in prey abundance than cod

larvae . Qualitative mismatches in prey. as evidenced hy Anderso11 1 1994). may bt.: mon:

limiting to rcdlish survival than quantitative mismatches. Laboratory experiments would

thus be useful in determining if I) larval redlish show biased preference for prey of

difll:rent quality oiTered at equal concentrations and 2) these choices subsequently aflt:ct

growth and survival .

Lastly. our understanding of recruitment variability ofredtish would greatly be

improved with feeding experiments conducted during the juvenile stage. Weight changes

after metamorphosis within the tirst year oflitt! in marine tish can exceed I 05 -fold for

some species. suggesting that gro\\tth rate variability during this stage could signiticantly

intluence recruitment (Houde 1987). Like the early larval stage of redtish. infonnation

76

on ju\·enik feeding dynamics is restricted to gut content analysis from a ft:\V tidd studics

( BainbriJ1.!c and McKav 1968: Anderson l99.l ). How the carlv lit~ tora!.!inlJ stratc!.!ics of - . . - e -

juvcnik reJtish changc \Vith changing prcy availability wouiJ thcrctorc bc uscful in our

understanding of post-larval matches and mismatches in food availability .

77

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