Acceptability of various microparticulate dietsto ®rst-feeding walleye Stizostedion vitreum larvae

K.M. GUTHRIE & M.B. RUST Northwest Fisheries Science Centre, Resource Enhancement and Utilization

Technologies Division, Seattle, USA

C.J. LANGDON Oregon State University, Hat®eld Marine Science Center, Newport, OR, USA

F.T. BARROWS US Fish and Wildlife Service, Bozeman Fish Technology Center, Bozeman, MT, USA

Abstract

The acceptability of eight diets made by a wide variety of

microparticulate manufacturing processes was studied using

®rst-feeding walleye Stizostedion vitreum larvae. Diets were

formulated using a common dietary mix but di�ered in

manufacture technique. The microparticulate diets fed were

(1) carrageenan bound, (2) alginate bound, (3) starch/

konjack bound, (4) microextruded/maurmurized1 (MEM),

(5) zein bound, (6) carboxymethyl cellulose bound (CMC),

(7) particle-assisted rotationally agglomerated (PARA) and

(8) a commercial microparticulate diet (Fry Feed Kyowa B-

700, FFK). Controls were groups fed live Artemia nauplii

and unfed. Gut fullness was measured as the cross-sectional

optical area of the bolus visible through the transparent body

of the larvae using computer-aided image analysis. Feeding

incidence on2 MEM particles (71 � 8%, mean � standard

error), zein-bound particles (69 � 7%), alginate-bound par-

ticles (68 � 2%) and PARA particles (65 � 6%) were not

signi®cantly di�erent (P 0.05) from the feeding incidence for

Artemia (71 � 6%). FFK (49 � 14%) and particles bound

with carboxymethyl cellulose (27 � 0.07%), starch

(21 � 10%) or carrageenan (20 � 0.8%) had signi®cantly

(P < 0.05) lower feeding incidence. Larvae that did initiate

feeding did not di�er signi®cantly (P > 0.05) in the amount

of each microparticulate diet or Artemia consumed. This data

indicates that once ®rst-feeding walleye start on a diet, they

will consume that diet to a similar ®xed level of satiation.

Given the di�erences in the amounts of water and nutrients

in the various diets, more nutrients were delivered to the gut

of walleye larvae feeding on microparticulate diets than on

the Artemia control.

KEYKEY WORDSWORDS: Artemia, feeding, larval, nutrition, start-feeding

Received 14 October 1997, accepted 25 January 19993

Correspondence: Michael B. Rust, Northwest Fisheries Science Center,

Resource Enhancement and Utilization Technologies Division, 2725

Montlake Boulevard East, Seattle, WA 98112±2097, USA. E-mail: mike.

rust@noaa.gov

Introduction

Walleye Stizostedion vitreum are an important sport and

commercial ®shery in North America, with a large geograph-

ical range (Hubbs & Lagler 1949; Trautman 1957; Becker

1983). In the USA, the value based on angler expenditures

was US $2.2 billion in 1991 (Summerfelt 1996) and in

Canada, walleye represented 16.3% of the total freshwater

®shes caught by anglers (Fenton et al. 1996). From 1990 to

1995, Canadian harvest of walleye ranged from 3.0 to 4.9

million kg annually. In 1992, ®shers in Canada received an

average of US $2.60 kg±1 for walleye netted from remote

natural lakes (Summerfelt 1996). High prices for walleye

resulted in interest in production of food-size walleye from

aquaculture (Summerfelt 1996). Most walleye aquaculture is

currently conducted by public agencies who culture fry and

®ngerlings in ponds for restocking purposes (Conover 1986;

FWS 1992; Heidinger et al. 1987). Nearly all commercial

walleye aquaculture is also targeted for sport ®sh enhance-

ment (FWS 1992).

Commercial production of walleye is limited to varying

degrees by di�culties in rearing the larval stages (Nickum

1986). At ®rst-feeding, walleye are small, possess a very

limited yolk reserve, start feeding with an incompletely

developed digestive system and have a comparatively short

lecithrotrophic4 stage (Balon 1975, 1984). Digestive function

changes during larval development, becoming more e�cient

as the larvae approach metamorphosis (Rust 1995). Before

metamorphosis, feed must be readily consumed and be

highly digestible to support good larval growth and

survival.

153

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Ó 2000 Blackwell Science Ltd

One of the impediments to intensive rearing of walleye

larvae is the lack of high quality microparticulate diets5 that

are acceptable, digestible, and which meet the nutritional

needs of the larvae. Microparticulate diets that are uniform

both in size and nutritional quality have been shown to

dramatically increase the rearing success of species such as

white®sh Coregonus clupeaformis (Zitzow & Millard 1988),

carp Cyprinus carpio (Lubzens et al. 1984), smallmouth bass

Micropterus dolomieui (Ehrlich et al. 1989) and muskellunge

Esox masquinongy (Zitzow 1986). Larval walleye have been

cultured wholly on formulated dry feeds; however, survival

and growth are generally low (Krise & Meade 1986; Nickum

1986; Loadman et al. 1989).

E�ective microparticulate diets should: (1) e�ciently retain

nutrients despite large surface area to volume ratios that are

conducive to rapid nutrient leaching after particles are

suspended in water; (2) possess physical and chemical

characteristics that result in their ingestion by ®sh larvae;

(3) be readily digested and assimilated by larvae; and

(4) consist of an optimal nutrient composition for maximum

larval survival, development and growth. This study address-

es the second requirement by comparing the acceptability of

eight types of microparticulate diets fed to ®rst-feeding

walleye larvae.

Materials and methods

Dietary treatments

Ten dietary treatments were applied to duplicate tanks of

®rst-feeding walleye. The treatments consisted of eight

preparations using a common dietary mash and two controls

(live Artemia and unfed treatments). Speci®c treatments

were: (1) carrageenan bound (particle size: 250±425 lm6 ),

(2) alginate bound (250±425 lm), (3) starch/konjack bound

(250±425 lm), (4) microextruded/maurmurized (MEM,

250±425 lm), (5) zein bound (250±425 lm), (6) carboxy-

methyl cellulose bound (CMC, 250±425 lm), (7) particle-

assisted rotationally agglomerated particles (PARA, 250±

425 lm), (8) fry feed Kyowa B-700 (FFK, 400±700 lm,

Biokyowa Inc., Chester®eld MO, USA), (9) live newly

hatched Artemia nauplii (430 lm, San Francisco Bay strain,

Bayou Brine Shrimp and Aquatic Foods, Onterio, CA,

USA7 ), and (10) unfed. Microparticulate diets were dispensed

every 15 min for 28 h by automatic feeders controlled by

timers. Each tank was fed a total of 12 g (as fed at 10%

moisture) of each microparticulate diet.

Artemia cysts were hatched in aerated sea water (30 g L±1)

at 28°C. The nauplii were decanted after 24 h and rinsed

prior to being fed to the walleye larvae. Feeding was (10 g

each tank, wet weight basis) over a 28-h period.

Fish and rearing

Larval walleye at their ®rst-feeding stage (4 days post hatch

at 19°C) were obtained from Garrison Dam National Fish

Hatchery (Riverdale, ND, USA). Larvae were held in one

tank supplied by a recirculation system for 2 days prior to

the start of the study. Random groups of 100 larvae were

stocked into 20 (10 treatments ´ 2 replicates) 30 L circular

tanks (radius 30 cm, depth 33 cm) from a batch of 30 000

larvae. All tanks were screened with nylon stockings over a

1000 lm8,9 nitex8,9 screen (Aquatic Ecosystems Inc., Apopka, FL,

USA) to retain feed in the tanks and supplied with

recirculated water maintained at 19.0 � 1.0°C by a

heat pump (Model #AHP6, Aquanetics, San Diego, CA,

USA). Recirculated water was pumped through a bio-®lter

(Model #BBF-2, Water Garden Gems, Borne, TX, USA) and

UV ®lter (Model #DZ401, Rainbow Lifeguard, El Monte,

CA, USA) prior to returning to the tanks. Lighting was

controlled by a timer to provide a photoperiod of 12 h dim

light/12 h dark. The 28 h trial began and ended during the

light phases.

Water quality was monitored daily as follows: Alkalinity,

ammonia and nitrite were determined with commercial test

kits (Model 16900±01, DR/700 methods 8038 and 8507,

Hach Chemical Company, Loveland, CO, USA), pH,

temperature and dissolved oxygen were monitored with

meters (Hach pH meter, YSI models 30 and 55 oxygen

meters, Yellow Springs Instruments, Yellow Springs, OH,

USA).

Diet preparation

The particle types being tested for acceptability included

various microbound particles (alginate, carrageenan, CMC,

starch, and zein; Langdon 1989), microextruded/maurmuri-

zed (MEM) particles, and particles produced by a rotational

agglomeration technique (particle-assisted rotary agglomer-

ation, PARA; Barrows et al. 1993). All diets incorporated the

same mash. The formulation of the mash has produced good

growth and survival as a sole food for larval walleye

(Table 1, walleye starter #9501) in previous trials (Barrows

et al. 1993).

Zein particles were made with 20.0 g of the mash com-

bined with 30.0 mL of 100 g L±1 zein (corn zein, ICN

Biomedical Inc., Costa Mesa, CA, USA10 ) dissolved in 90%

ethanol. The ethanol was removed by evaporation.

K.M. Guthrie et al.

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Ó 2000 Blackwell Science Ltd Aquaculture Nutrition 6; 153^158

154

Alginate particles were made with 30.0 mL of 1 MM

Na2HPO4 added to 20.0 g of mash. After mixing, 30.0 mL

of 20 g L±1 sodium alginate (Protanol LF 120, Pronova

Biopolymer Portsmouth, NH, USA)11 solution was added with

vigorous mixing. Finally, 5.0 mL of 10 MM calcium chloride

was added to gel the mixture.

CMC particles were made with 80.0 mL of 20 g L±1

carboxymethyl cellulose (F99±7HF, Hercules Inc. Wilming-

ton, DE, USA12 ) solution mixed with 20.0 g of mash. Finally,

5.0 mL of 10.0 MM calcium chloride solution was then added

to the gel mixture.

Starch/konjac particles were made with 20.0 g of mash

mixed with 30.0 mL of distilled water and 2.3 g of a

commercial mixture of starch and the gum konjac (Nutricol

GP 440; FMC Corporation, Philadelphia, PA, USA13 ). The

mixture was heated to 80°C and 1.5 g of sodium carbonate

was added to help gel the mixture upon cooling.

Carrageenan particles were made with 20.0 g of mash

combined with 30.0 mL of 1 MM Na2HPO4 and 30.0 g of

carrageenan (Gelcarin GPB 12, FMC Corporation). This

mixture was heated to 80°C to dissolve the carrageenan. The

mixture was gelled by addition of 7.0 mL of 2.5 MM KCl and

then allowed to cool to room temperature.

All microbound diets were freeze-dried, ground with a

pestle and mortar, then separated through a series of sieves

agitated on a Rototap (Tyler Inc., Gastonia, NC, USA14 ) to

produce particles of acceptable size.

Data collection and analysis

Data collections followed the method of Rust & Barrows

(1998). At the end of the feeding trial, tanks were cleaned of

uneaten feed and waste. All ®sh in each tank were collected in

a sieve (750 lm15 ) and preserved in 100 g L±1 bu�ered forma-

lin. Feeding incidence was determined by observation of

larvae under a microscope and counting the number of full

and empty guts. Ten feeding larvae (i.e. only larvae that had

feed visible in the gut were used for gut fullness measure-

ments) from each tank were video-taped and digitized to

determine bolus cross-sectional optical area (an index of feed

consumption) using a Macintosh computer (Apple Computer

Inc., Cupertino, CA, USA) and NIH Image software (US

National Institutes of Health, http://rsb.info.nih.gov/nih-

image/).

Mean consumption (10 ®sh per tank) and incidence (100

®sh per tank) values for each tank were considered units of

observation for statistical comparison (two observations per

treatment). One way analysis of variance was used to

determine signi®cantly di�erent dietary treatments

(P < 0.05) using a computer statistic software (STATVIEWSTATVIEW,

Brain-Power, Calabasas, CA, USA). Means were separated

by the protected least-squares method. Per cent feeding data

was arcsine transformed prior to statistical analysis.

Results

Water quality

Alkalinity measurements averaged 113.0 � 4.6 mg L±1

CaCO3 (mean � standard error); the average pHwas 7.51 �

0.12. Average ammonia nitrogen was 0.27 � 0.26 mg L±1

(NH3-N), average nitrite was 0.16 � 0.09 mg L±1 (NO2-N)

and the average temperature was 20.6 � 0.11°C.

Feed

The percentage of larvae feeding on four of the micropar-

ticulate diets did not di�er signi®cantly (P > 0.05) from live

Artemia (71 � 6%, Fig. 1). These diets were: (1) MEM

particles (71 � 8%), (2) zein-bound particles (69 � 7%),

(3) alginate-bound particles (68 � 2%) and (4) PARA

particles (65 � 6%). Feeding incidence for the commercial

control diet FFK (49 � 14%) was intermediate. Particles

bound with carboxymethyl cellulose (27 � 0.07%), starch

(21 � 10%) and carrageenan (20 � 0.84%) were accepted

at signi®cantly lower levels (P < 0.05).

The optical cross-sectional area of the bolus in feeding

larvae was similar (P > 0.03) for all dietary treatments

except in the unfed control (Fig. 2). This indicated that all

diets were consumed by feeding larvae to a similar degree,

although the within-treatment variability increased with less

acceptable diets. The mean cross-sectional areas for

each treatment were as follows: Artemia 1.11 � 0.10 mm2;

PARA particles 1.05 � 0.01 mm2; MEM particles 1.03 �

0.10 mm2; zein-bound particles 1.03 � 0.02 mm2; alginate-

bound particles 0.98 � 0.20 mm2; carboxymethyl cellulose

particles 0.95 � 0.20 mm2; FFK 0.92 � 0.20 mm2; starch

particles 0.89 � 0.40 mm2 and carrageenan particles

0.72 � 0.60 mm2.

Table 1 Formulation of mash used in all microparticulate diets

Ingredients g kg)1

Artemia meal 86Egg solid 216Fish meal 145Fish oil 44Krill meal 410Liver meal 76Yeast extract 23Total 1000

Acceptability of various microparticulate diets

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155

Nutrient delivery

The amount of binder and moisture can alter the e�ective

`payload' of mash or nutrients delivered to the gut of the

larval ®sh. Microparticulate diets varied in the ratio of binder

to mash. In addition, live Artemia have a much lower

nutrient density than microparticulate diets because of the

di�erence in moisture. Table 2 shows the percentage payload

for each diet, the consumption of each diet expressed as a

percentage relative to the treatment with the highest con-

sumption (in this case, live Artemia) and the product of the

two, which represents the relative dry matter payload of

nutrients delivered to the larval gut. In terms of dry matter

nutrients delivered to the gut, all the microparticulate diets

were similar to, or higher than live Artemia, even though

more Artemia was consumed on an `as fed' basis.

Discussion

Feeding incidence (% of larvae feeding) represents the

decision on the part of the larva to ingest a feed item for the

®rst time. A larva with only one particle in the gut counts

just as much as a satiated larva. Conversely, feed consump-

tion (gut fullness), measured as the cross-sectional optical

Figure 1 Feeding incidence of ®rst-

feeding larval walleye after 28 h expo-

sure to various microparticulate diets or

live Artemia. PARA is particle-assisted

rotationally agglomerated microparti-

cles; MEM is microextruded then ma-

urmurized; CMC is microbound with

carboxymethyl cellulose; FFK is Fry

Feed Kyowa, a commercial micropar-

ticulate diet. Error bars represent stan-

dard errors. Lower case letters indicate

signi®cant (P < 0.05) di�erences.

Figure 2 Feed consumption of ®rst-

feeding larval walleye after 28 h expo-

sure to various microparticulate diets or

live Artemia. Consumption was mea-

sured as the cross-sectional optical area

(mm2) of the bolus. Error bars represent

standard errors. Lower case letters indi-

cate signi®cant (P < 0.05) di�erences.

K.M. Guthrie et al.

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Ó 2000 Blackwell Science Ltd Aquaculture Nutrition 6; 153^158

156

area of the bolus, represents a repeated decision to ingest feed.

Measuring consumption by determining the cross-sectional

area of the bolus maybe more meaningful than by other

methods, such as counting particles. Even if diets di�er in

moisture content and particle size, or if gut passage times

di�er, the total size of the bolus will be an accurate re¯ection

of the volume of feed consumed (Rust & Barrows 1998).

In this study, feed incidence varied with diet type while

feed consumption did not. This indicates that once a diet is

initially ingested, larval walleye will continue to ingest it to

more-or-less the same degree. Once walleyes begin to accept

diet, the positive reinforcement of odour, taste and satiation

may result in increased and continued consumption (Rottiers

& Lemm 1985).

It is not clear whether vision or olfaction are more

important in locating feed for larval walleye. Iwai (1980)

suggested that chemical senses may be e�ective in perception

of feed by larval and juvenile ®sh because their ®eld of vision

is limited, especially at night. Rottiers & Lemm (1985)

suggested that when the larvae are relatively immobile, the

sensory function of the exposed olfactory organ may be

important in the imprinting of permanent behavioural

responses to various olfactory sensations. The size or age

when the olfactory organ become functional in walleye is not

known. In our study, walleye larvae accepted a wide range of

particles types, including MEM and PARA particles, to the

same extent as Artemia. Both sight (Mathias & Li 1982) and

taste of feed may have had signi®cant e�ects on feed

acceptance. PARA and MEM were the darkest in colour

and most closely resembled the colour of Artemia, which

could explain why feeding incidence was similar. Conversely,

the freshwater zooplankton that make up the natural diet of

larval walleye are translucent. In addition, the ¯avour or the

lack of ¯avour of each diet, owing to the di�erent binders,

may also explain the results. Feeding may also have been

e�ected, to some extent, by odours circulated from one

treatment to the others via the water recirculation system

used in this study. Further experiments using a single

microparticulate diet type with di�erent colours or feed

attractants using a ¯ow-through water supply could be used

to address such possibilities.

A high percentage of ®rst-feeding walleye accepted the

microparticulate feed without ®rst exposure to live feed, as in

other experiments (Masterson & Garling 1986). Clearly, the

movement of a live prey item is not necessary to initiate

feeding in larval walleye.

The results of this study indicate that while walleye larvae

will actively feed on several types of microparticulate diets,

they do show marked preferences for some types over others.

Particles that are highly acceptable to larval walleye, such as

PARA, MEM, zein-bound and alginate-bound particles still

need to be digestible and correctly formulated to support

good growth and survival. Diets which are not highly

acceptable, such as those bound with CMC, carrageenan

and starch, would only support survival and growth if high

nutrient availability and density were possible.

Further studies are needed to determine optimal dietary

characteristics and environmental parameters for intensive

larval culture of walleye with microparticulate diets. Once

methods are developed to produce high and consistent

feeding incidence and maximal feed consumption, then work

on improving formulation and digestibility can proceed.

Acknowledgements

This study was supported in part by grant

NFFMP299600005 from the Saltonstall-Kennedy grant pro-

gram. The authors wish to thank Jihye Kim and Ken Massee

for their help and support in the wet laboratory. The authors

thank Rob Holms and Matt Bernard at Garrison Dam NFH

for providing the larval walleye and Dr Conrad Mahaken,

Dr Robert Iwamato and two anonymous reviewers for

critical review of the manuscript.

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Table 2 Payload of dietary ingredients delivered to the gut of larval

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Diet/Binder TypePayload(%)

Consumption(%)

Payloaddelivered (%)

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Acceptability of various microparticulate diets

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K.M. Guthrie et al.

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Ó 2000 Blackwell Science Ltd Aquaculture Nutrition 6; 153^158

158