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ON THE OCCURRENCE OF ECTOCOMMENSAL CILIATES ON
Metapenaeus dobsoni (MIERS) IN RELATION TO
WATER QUALITY PARAMETERS IN POND ECOSYSTEM AT VYPEEN
DISSERTATION SUBMITTED
Miss DEEPA K. G.
IN PARTIAL FULFILMENT FOR THE DEGREE Ol- MASTER OF FISHERIES SCIENCE (MARICULTURE)
OF THE
CENTRAL INSTITUTE OF FISHERIES EDUCATION (DEEMED UNIVERSITY)
-..I.:!'.
**,. s-Q. 7 - ^
JULY 1997
POST GRADUATE PROGRAMME IN MARICULTURE
CENTRAL MARINE FISHERIES RESEARCH INSTITUTE
COCHIN - 682 014
O 'riificd ili.ii ihe dissert.tiion m tillt 'd 'O N THE OCCURRENCE OF ECTO COMMENSAL
CILIATES ON Metapennvus ihbnoni (MIERS) IN RELATION TO WATER QUALITY
PARAMETERS IN POND ECOSYSTEM AT VYPEEN' is boti.ifide recortl of work done by
Miss Det*pa K.G. under our j>,uid.ini (‘ <il llu* Central M.\riiu* I isheries Research InstiluU-
during tiu' l(*nure of her (M<iri( iilluri?) fVogrfUnine o( - 1^)97 nnd llia! it h.is
not previously foriDed the l».isis for iiu* .iw.ird of any other degree;, di[jloni.i or oiliet
siniilnr titles (jr for any puliiic alion. ^
Shri. K.G.Cirija Vallnbhan,Seti io i Sc icn t is t ,
(I.M.I.K.I, (xK'hin,
Metiil)(M', A f l v i s o t y ( 'o in in i t t e e .
Dr. (Mrs) Mary. K.Manissery,Senior Scientist,C.M.F.R.I., Cochin,M a jo r Advisor,
A flv isory Com tnillee.
Dr. P.C.Thomas,S en io r Sc i t 'n t is l ,
( .M .r .K .I., C 'ochlii^
McMiiljef,
A d v is o r y C 'on i tn i l tee .
j B g c l a r a t m n
I hereby declare that this thesis entitled 'O N THE OCCURRENCE OF ECTOCOM-
MENSAL CrLIATES O N Mefapenaeus M s o n / IN RELATION TO WATER
QUALITY PARAMETERS IN POND ECOSYSTEM AT VYPEEN^ is based on my own
research w ork and has not previously formed the basis for the award o f any degree,
diploma, associateship, fellowship or other similar titles or recognition.
Cochin - 682 014 July, 1997
DEEPA K.G,
m m
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i t ^ ^ ^^ id i ii ^ w 3iffeR{ q i 3fk ^ ^ ii
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CONTENTS P age No.
1. Preface 1
2. Acknowledgement 2 - 3
3. Introduction 4 - 8
4. Materials and Methods 9 - 1 7
5. Result 18 - 25
6. Discussion 26 - 34
7. Summary 35
8. Reference 36 - 41
9&
PREFACE
Fishery sector has a place of pride in the national economy of India. Shrimps are the single
item in the basket o f marine products with universal taste-reraain the backbone of Indian
marine product export. Due to the declining trend o f prawn catches from the sea, brackish
water and fresh water prawn farming has immense scope to fulfill the growing demands of
the population. The culture practices are mostly restricted to Penaeus sp. obviously be
cause of certain special qualities attributed to it. However, in traditional prawn culture,
practised in coastal waters, prawns other than Penaeus sp. also enter the culture system and
grow. Thus about 60-80% of the catch is contributed by Metapenaeus dobsoni and smaller
sizes o i Penaeus indicus. M. dobsoni forms a major part o f the all India landing of prawn
followed by P. indicus and P. monodon.
One of the major problems faced by prawn farmers is the vulnerability o f these animals to
c o n t i ^ diseases. The most important requirement o f any type of culture system is clean
water. Environment and water quality parameters may be direct or accessoryocLlological
factors (Stressors) o f prawn diseases. General environmental conditions, substrate charac
teristics and physical, chemical and biological components o f the culture medium are in-
eluded in this broad category. When populations o f stressed animals are dense, even low
levels o f stress may give pathogen an opportunity to enter upon the exponential segment ol
iheir growth curves and cause devastating epizootics. A number of diseases are of undeter-
minedactiology. Even in cases where etiology is known, our understanding ol the host-
agent-environment interaction is incomplete.
The present work is an attempt to fmd out the relationship between ectocommcnsal ciliates
in Metapenaeus dobsoni and water quality parameters.
ACKNOWLEDGEMENT
I am deeply indebted to Dr.(Mrs.) Mary. K. Manissery, Senior Scientist,
C.M.F.R.I., for her inspiring guidance. I am extre. i^ly grateful to Dr. P.C.
Thom as, Senior Scientist, C.M.F.R.I., for his valuable suggestions and timely
help . I am thankful to Mr. K.G.Girijavailabhan, Senior Scientist, C.M.F.R.I.,
for providing vehicles for transportation o f live specimens, without w hich it
would not have been possible to complete this work in time.
I express my sincere thanks to Dr. M.Devaraj, Director, C.M.F.R.I., Cochin
for all the facilities provided,
I record my gratitude to Dr. C. Suseelan, Officer -in -charge, RG.P.M.,
for his timely help in the course of study.
My sincere thanks are due to Dr. S.M.Pillai, O.I.C., C.I.B .A., Narrackal
for all the facilities that enabled me to com plete my experim ents in time. I
also express my deep gratitude to Dr. K.S. Purushan, O.I.C., F isheries Station,
Kerala Agricultural University, Puthuvej'ppu in Vypeen Island for space and
f a c i l i t ie s e n ab l in g m e to do the d i s s e c t io n s and c o n d u c t m ic ro s c o p ic
examinations.
I am thankful to Senior Scientists M r.S.M uthusam y, Mr.G.S. D anie l
Selvaraj and Mr. P E . Sampson Manickam for the constructive criticisms and
suggestions. I am grateful to Senior Scientists Dr. V. K unjukrishna Pillai, Dr.
C.P. G o p in a th an , D r.V .N eelakan ta P i l la i , Dr. (M rs.) V. C h a n d r ik a , Dr.
K.Rangarajan for providing laboratory facilities that enabled me to analyse
the samples.
I thankfo^ ' ackBowIedgetechnical officers Mr. A. Nandakumar, Mr. K_A.
U n n ith an , M rs, K .S . L ee la Bhai, Mr. N. P a lan isw am y fo r th e ir t im e ly
assistance. My special thanks are due to Mr. P. Raghavan, Technical Officer,
for the excellent photographs.
I am very m uch obliged to Mr. M angesh M adhukar Shirdhankar who
g en e ro u s ly donated tim e to help me in s ta tis tica l ana lys is o f the data . I
gratefully acknowledge Mr. Manoj Nair. R.and Mr. Ranjit.S . for helping me
in taking m icrophotographs.
I am indebted to my friend and colleague Miss. Nisha.P.C. for being a
strong source of encouragem ent and support during the work.
I w ish to thank all my colleagues and Ph.D scholars for their kind help '
through out this project.
F in a l ly I g ra tefu lly ack n o w led g e I .C .A .R ., C . I .F .E . /C .M .F .R .I . , for
granting the fellowship enabling me to undergo the Post G raduate Program m e
in M ariculture.
I N T R O D U C T IO N
Among the more serious diseases o f shrimps are those caused by non-infectious
epicommensal organisms. Almost all aquatic habitats are used or exploited by some spe
cies ol’pcritrichous ciliales. Both sessile and mobile forms ol'peritrich make cxlciisive use
o f the tegument o f both invertebrates and vertebrates as substrates upon which to live and
reproduce. Many peritrichs are epibionts (epizoonts, ectocommensals or ectoparasites)
(Couch, 1983). Crustaceans are known to harbour severai species o f ectocommensalic cili-
ates especially peritrichs (Kidder and Summers, 1935; Stiller, 1953; Kane, 1965; Couch,
1971). An encysted form o f an unidentified apostome ciliate, associated with black gill
disease in Penaeus duoranim has been described by Couch (1978). Another ciliaie
Parauronema sp. has been observed by Couch (1978) in the haemocoel ofprotozoea, mysis
and juvenile stages o f living, moribund and dead Penaeus aztecus. Suctorians such as
Acineta sp. (Johnson, \9 1 ^E p h ilo ta sp. (Couch, 1978) and E. g-^.mnipara (Gucalan et al.,
1979) have also occasionally been encountered on the body and gills o f penaeid prawns.
Protozoan associates found in the estuarine shrimp Metapenaeus monoceros (Fabricus) and
the tenaidacean Apseudcs chilkcnsis (Chillon) from Cochin backwalcrs have been dcscribccl
by Santhakumari and Gopalan (1989). A peritrich ciliate Zoothamnium rigidiu/n (Prechl).^a
heterotroch Stentor coeruleus (Bhrenberg) were reported in both the hosts. Another cilialc
Lugenophrys cochinensis was observed on the tenaidacean (Santhakumari and Gopalan,
1980). A variety o f ectocommensal protozoans including Epistylis sp., Colhurnia sp., Acineta
sp., Zoothamnium, Lagenophrys have been observed on the carapace o f wild crawfish and
rarely for the gill chambers (Scott and Thune, 1986).
With the exception o f Shomey’s (1955) Couch’s (1971) and Overstreet’s (1973) works, no
studies concerning epizootics of commensal peritrichs on natural population ol'crustaceans
have been reported. (1) seasonal prevalence of ciliate Lagenophrys callinectes in the natu
ral population of blue crab; and (2) seasonal intensity o f infestation of individual hosts: both
in relation to seasonal behaviour o f the host was studied by Couch (1966, 1983). Rclalively
high rate o f infestation with more dense growth o f larger colonies observed on the reared
individuals than those collectcd from the nature, which showed the probable conduciveness
o f stagnant vv^ater and overcrowding for infestation as has been observed by Ovcrstreei
(1973). Species ot'Zoolhamnium infestation is rare to moderate in cultured populations and
rare in individuals of wild populations (Overstreet, 1970; Sanfhakumari & Gopalan, 1980;
Soni, 1986). ' ^ i
Heavy infestation o f an encysted form (pleuront) o f an un-identified apostome ciliate, asso
ciated with blue gill disease in Penaeus duorarum occurs on the gills o f prawn during
periods o f warm to moderately cool weather (Couch, 1978). Seasonally infestation is mod
erate during pre-monsoon (April to June) and rare during other months (Soni, 1986).
In a healthy environment penaeids can toleratet a large number o f these epicommcnsals
with no apparent detrimental effects. The protozoan epibiont Zoothamnium sp^^Jia.s been
reported to preferentially locate on the gill lamellae Mcicrobrachium while other proto
zoan epibionts do not show site specificity (Hall, unpubhshed data), Shomcy (1955) and
Couch (1973) have examined the physical relationship o f the lorica and trophoiils of
Legenophrys sp. to the tissue o f their host. Heavy inlestation o f a cuticlc covering ccU)
commensal protozoen could interfere with proper respiratory or excretory functions o f host
gili tissue (Couch, 1967, 1978; Overstreet, 1973). Johnson (1972) has attribnlcd instances
o f mortality o f pond-reared shrimps to infestation o f species o f Zoothamnium sp. Stalked
peritrich such as Vorticella sp., Zoothamnium sp., Epistylis sp. and Lagenophrys iunatiis
are generally found attached to gills, appendages and body surfaces o f larval, post-larval,
juvenile and adult penaeids^o^the gill can cause hypoxia and death {Overstreet. 1973,
1978). Couch (1978) has pointed out that certain species of the genus Ephilota may act as
stressors in infected prawn while E. gemnicola infestation on P. monodon larvae in rearing
tank has been implicated for weakening and mortality of the populations (Gucaten et ciL,
1979). I'he deterioration of exoskeleton due to overcrowding of this ciliate might serve as
portals for other harmful organisms such as bacteria and fungi, capable of producing seri
ous shell diseases (Rosen, 1970; Gopalan and >^ n g , 1975). This can lead to morlality of
the host (Overstreet, 1973). However epizootics o\'Epistylis sp. •fouling on otherwise healthy
appearing sub^adults and adult prawns in which upto 40% of the pond population were
affected have infrequently occurred in Hawaiian prawn ponds (Brock, J.A; unpublished
data, 1981).
However heavy infestation oi'Zoothamnium sp. in the gills of'crowded pond reared shrimps
in conjunction with low dissolved oxygen levels have been implicated in mass mortalities
o f cultured stock in Texas & Louisiana (Johnson et a i, 1973; Overstreet, 1973). Kxperi-
mental infestation of Z. rigidium in shrimp and the effect of stress produced by high turbid
ity and low oxygen tension in the infested prawns were carried out by Overstreet (1973) and
in Lenaidecean by Santhakumari and Gopalan(1980). Ligi'uner (1977) and Fisher (1977)
have indicated that epibionts may restrict gas exchange by accumulating on eggs and gill
surfaces in susceptible crustaceans, thus causing mortality through asphyxiation.
Johnson ei a/^^JJ_973) reported the loss of an estimated 2000 pond held prawn ^^ewhite
shrimp in a single day, due to the presence of large numbers oiZouthamniiun sp. on the gills
and a reduction in dissolved oxygeji levels. Mortality was attributed to anoxia as (he nior-
talities occurred when the infestation o f ciJiates became heavy enough to restrici i)X)'gen
exchange and when the dissolved oxygen levels in the pond dropped below 3 ppm to a low
level o f 2.6 ppm. Death occurs when the effective respiratory surface o f the gill is reduced
by presence o f numerous colonies o[' Zoothamnium species and subsequently the suiToca-*
lion of the animal (Lightner, 1975). Death usually coincides with periods o f low concentra
tion of dissolved oxygen in the water, a common condition following several warm over
cast days or following decomposition o f large algal blooms (Overstreet, 1975). Lightner
(1975) pointed out that in normal conditions, when Zoothamnium sp. was absent, dissolved
oxygen levels o f 2.6 ppm was not lethal, as good survival was experienced with Penaeiis
aztecus in culture ponds, even when the dissolved oxygen levels fell to 1 ppm. Rajendran e/
, ^ al^JJ^9^2) reported that protozoans are found to affect the juvenile prawns in the culture
ponds where the dissolved oxygen levels in pond water decreased to 1 ppm due to non-
tlushing of pond water with tidal water.
Soni (1986) in his doctoral thesis reported mortality due to heavy infestation ofZoothamnhim
sp. in culture ponds at Valappu (Cochin, Kerala) when the dissolved oxygen level was as
low as 2.36 ppm. The gills o flhe affected pr^wnj were found to be heavily infested with
Zoothamnium. Sp. Later, llameed (1989J reported that Zoothamnium infestalion in
protozoea of prawn can cause reduction in its heart beat and further in the infected larvae,
the heart beat stopped its continuous beating frequently and started functioning again alter
an interval o f 5 seconds. The virulence was also observed to be rather slow in the inlested
larvae as compared to that o f the normal and healthy ones.
Bctocommensal ciliates utilize crustacean cuticular surface as the substrate for attachment
and rely on concentrated bacterial population found in water with high organic load for
nourishment. As water quahty deteriorates bacterial concentration increases and in such
conditions peritrichous ciliates such as Cothurnia sp., Epistylis sp. and Zoolhaniniuin
sp. which feed on bacteria flourish. Conversely the presence o f the suctorian Acineia which
is saprotrophic on ciJiated protozoans suggests that organisms higner in the food web than
bacteria are present (Scott and Thune, 1986). Incidence o f peritrichous c\\r<xi& Cothurnia
sp. and Epislylis sp. both bacteriovores increase with increased turbidity. ^Sawyer el al.
0976Xsuggested that suctorian Ephilota sp. found on lobster and ;ock crab may be useful
as an indicator species. Brock (1983) reports species o f Epistylis infestation in
Macrobrachium hatcheries in association with extremely poor water quality conditions pos
sibly resulting from lack of adequate pond water turn over. Scott and Thune (1986) found
significant correlation between the incidence of ectocommensals and primary productivity
on freshwater red swamp crawfish Procambariis clarkii (Girard). Hudson and Lester (1992)
worked on the relationship between water quality parameters and ectocommensal ciliates
on prawns {Penaens japonicus Bate) in aquaculture and found out that as the water quality
decreased, the number of Zoothamnium sp. increased and the number o f Cothurnia de
creased.
The present study was carried out in the prawn culture fields at Vypeen island in Cochin
backwaters. Cochin backwaters form an integral part o f Vembanad lake-the largest back
water system in Kerala, India. This backwater system is connected to the Arabian sea at two
points - one at Cochin and the other at Munambam through which seawater enters into the
backwater due to tidal influence.
EKperimsntal pond at Puthuveyppu
MATERIALS AND METHODS
S i te Se lec tio n :The present study on the relationship between ciliate
infesta tion on Metapenaeus dobsonijand water quality param eters was carried
out in a pond ecosystem at Puthuveyppu at Vypeen island.
A r e a o f S tudy : Site for the study o f ciliate infestation on M .dohsoni
... r : . j !_ -----j _* r»„*i-------- u__________________ :__________l i AV ' U JiJ <1 • 'V/ l lU t i l 1 U m V* V I IIU * oi> >1.
approximately O.lha. The water depth was about Im. The pond was having a
clay bottom. It was connected to the feeder canal through a sluice gate.
Stocking was done in this pond by letting in tidal w ater into the pond
during high tide. The juveniles were trapped as the tidal w ater recedes at low
tide by putting a screen across the sluice gate.
S tu d y Period: The present study was carried out for a period o f one
month during June 1997. The time o f sampling was fixed at 10.30-11.00 A.M.
Id e n t i f ic a t io n o f th e p r a w n : Body slightly tom en tose in pa tches .
Rostrum extending a little beyond the dorsal teeth and having a well m arked
double curve. Antero-lateral angle o f the carapace without spine. The inner
antinnular flagellum larger than the outer, extending its peduncle in length.
The last pair of thorasic legs do not nearly reach the m iddle o f the antennal
scale.
Colouration : The antinnule, antennae and antennal scales are doited with
red. T here is a double row of reddish spots on the telson, the margin being
greenish.
M e th o d o f S tu d y: Weekly samples ofM.dobsoni and water and sediment
samples were taken at the same time. M .dobson i^ ting a bottom dweller, it
was decided to collect w ater samples from a depth of about 10cm above the
bottom o f the pond.
/
Experimental prawn/Ml dobsoni
Sam pling o f Prawn: SampJing of p raw ns {M.dobsoni) was done every
week using cast net. They were transferred to a well -aera ted 12 Itr plastic
bucket containing the pond water, for live examination. A bout 20 prawns were
random ly selected for analysis.
S a m p lin g o f w a ter a n d S e d im e n t: Ambient w ater tem perature was
recorded at the site i tself using a mercury therm om eter w ith 0-50 calibrations.
Water samples were collected in two I Itr. polypropylene bottles for the analysis
o f the nutrients and total suspended solids (T^s.s.). Bottles for nutrient analysis
was fixed immediately with 1ml chloroform. All the bottles w ere washed twice
with am bient water before sampling. To estim ate the d issolved oxygen (d.o.)
125ml reagent grade corning bot^es with B.O.D . stopper was used. To estimate
. ^ e d . o . content of the w a t ^ ^ o t t l e was inHpjcrsed into the water. Care was
taken not to entangle any air bubble w hile collecting the water. The bottles
were re-stoppered inside the water column. The oxygen bottle was immediately
fixed by 1ml each of w inkler A and winkler B. Precipitate form ed was allowed
to d ispe rse un iform ly th rough out the bo tt les . W ater sam ple for sa l in i ty
estimation was collected in 100ml glass bottle and stoppered tightly. All the
water samples were chilled during transportation.
Sedim ent sample for pH determ ination was collected using a p.v.c. pipe
o f l in c h diameter. pH was determ ined using Universal Ind ica to r so lu tion
(Glaxo India Ltd.)
E x a m in a t io n o f P ra w n s: Live sam ples of M.dobsoni w ere b rough t to
the laboratory im m ediately after co llection. Size and sex o f the prawns were
recorded. Since ciliates are seen concentra ted mostly on the gills, only gills
were exam ined for occurrence of ciliate infestations. B ranchiosteg ite or gill
cover on the left side o f the prawn was cut open to expose the crescent shaped
gills. It was observed the gills increased in size from an terio r gill to the
posterior gill. The gills w ere seen attached to the thorasic wall at the m iddle
o f its length only and the point of attachment is called gill -root. Gills were
d issected out using a forceps and placed on a glass slide containing a few
drops o f pond water. The gills were grouped into three-anterior, middle and
posterior. They were examined under a compound microscope after putting a
cover slip. The num ber o f ciliates per gill were counted and the individual
ciliates were identified using standard keys (Kudo, 1966).
Prevalence o f ciliate infestation in the population o f M .dohsoni was
calculated as the total number of infested prawns divided by the total num ber
o f p raw n s exam ined . This value when m ultip lyed by 100 will g ive theV
percentage prevalence o f ciliate infestation in M.dobsoni for that day. Similarly
abundance was calculated as the total number of ciliate observed in the gills
divided by total number o f infested prawns. For the calculation of total number
) of ciliates, their numbers on the anterior, middle and posterior gills were pooled
together, for all the animals and divided by num ber of infested prawns.
To study the size prefarence o f ciliate about lO lp raw ns samples were
analysed for infestation. The prawns were grouped into various size groups of
lOmm size and prevalence and mean intensity o f infestation was calculated as
mentioned earlier.
L abora tory ana lys is o f the w ater sam ple : Water samples brought from
the field were analysed for the various hydrographic parameters. Determination
o f sa l in i ty , d^_^Ls.s ., phospha te and n i tra te w ere m ade using s ta n d a rd
procedures.
RT.O
Analysis
The water samples for oxygen^alini^utrients and total suspended solids, brought
back to the laboratory were analysed as follows
S a lin i ty
Reagents required :
1. Silver Nitrate (24.5 gm/Utre)
2. Potassium Chromate - (10%) 10 gms in 100 cc.
3. Standard Sea Water
Procedure:
Pipette out 10 cc of Standard Sea water into a 250 cc conical flask. Add 4 drops
of potassium chromate solution and using a mechanical Stirrer titrate aganist silver
nitrate solution. Repeat to concordance. Pipette out 10 cc of the sea water sample into
the conical flask and proceed as above.
Salinity is calculated as follows :
Let Volume of Silver nitrate for 10 cc standard Sea water = VI
Volume of silver nitrate per 10 cc Sample = V2
Salinity of Standard Sea water = S
Salinity of sample = V^ x S •
D issolved O x y g en .
Jteagenis
1. Sodium Thiosulphite solution (1.25 gms in 1 litre).
2. Starch solution - I gms starch made into a paste with distilled water and diluted
to 100 cc. boiled and kept.
3. Winkler Solution - A (20 gms of Manganese chloride in 100 ml water).
4. Winkler solution - B (41 gm of sodium hydroxide +25 gm of potassium iodide in
100 cc water).
5. Concentrated hydrochioric Acid.
6. Standard potassium iodate. ( Accurately weigh out 0.1784 gm of potassium iodate
ir)in 1 i(tf- vnlinnetric flas;rc nnd dissolve and make un to the volume. Tliis is
0.005N).
7. Potassium Iodide.
Procedure
Collect the water sample in a 125 ml glass stoppered bottle without entangling
any air bubbles. Take out the stopper and add Icc each of Winkler - A and winkler - B
solution. Close the bottle. Shake the bottle gently till the precipitation formed is evenly
distributed. Allow to settle. Then add 2ml conc. hydorochioric acid, close the bottle
and gently shake till the precipitate is completely dissolved.
Pipette out 10ml of potassium iodate solution into a conical flask. Add 1 gm of
potassium iodate and 2 ml of conc. hydrochioric acid. Dilute to 100 ml and titrate \ -iJ
against sodium thisulphate solution till the blue colour disappears, \ ' '' ' t
Pipette out 100 ml of the preserved sample and titrate against std. sodium
Ihiosulphate as above.
Calculation
Calculate the normality of potassium iodate as N, = Weight / litre
35.67
Titrate value of thiosulphate for 10ml of potassium iodate = V,
Calculate normality of thiosulphate as = N, x 10
V,
Hence amount of dissolved oxygen in ml/litre = Vj x x 8 x 1000 x R
100 X 1.429
(Where 1.429 being weight of 1ml of oxygen in miligrams. R is icnown as the
corrections factor and which is roughly equal to 1.01 in majority of the cases)
R e ac tiv e P h o s p h o ru s
Reagents
1. Ammonium molvbdate solution
15 gms of A.R. quality Ammonium molydate in 500 ml distilled water. Store in
plastic bottle, keep av/ay from sunlight.
2. Sulphuric Acid Solution
140 mi o f A.R. quality sulphuric Acid added to 900 ml o f distilled water.
3. Ascorbic Acid solution.
Dissolve 27gm of ascorbic acid (A.R. quality) in 500ml distilled water. Freeze—
the sqluxiofl-andi'or u s e b r i n g to labofatoi^'^efflpefature. After use again
freeze the solution. ^
4. Potassium Antimony tartrate solution.
Dissolve 0.34 gm of good quality of potassium Antimony tartrate in 250ml
distilled water.
5. Mixed Reagent.
Mix together 50 ml of Ammonium molybdate. 125 ml of Sulphuric Acid, 50 ml
o f Ascorbic Acid and 25 ml of Antimony tartarate solution. Mix well and the
solution can be kept for 6 hours. And the above quantity is sufficient for about
50samples.
Procedure.
To 10ml of sample at laboratory temperature add 10 ml of Mixed Reagent. After
5 minutes and preferably within the first 2-3 hours measure the extinction of the solution,
in a 10 centimeter cuvette at a wave length 8850® A units in a spectrophotometer.
Phosphate Standard.
Dissolve accurately 0.816 gm of anhydrous potassium dihydrogen phosphate in
1000 ml o f distilled water. Store in a dark bottle with 1 ml o f chloroform. 1 ml o f the
solution = 6|ig. at. / Itr phosphate phosphorus. 1 ml of this solution is made upto
100ml. From this 5ml is taken and diluted to 100ml. 100 ml sample is taken in a
conical flask, and 10 ml o f mixed reagent is added to the standard and sample. After
10 minutes the colour comparison of these 2 solutins is made in a Spectrophotometer.
The strength of the colour developed being proportional to amount of phosphate,
calculate the phosphate concentration in sample using the standard sU-ength of the
standard potassium phosphate solution.
Nitrate
Reagents
1. Phenol solution.
Dissolve 46 gm of dry A.R. quality phenol in 1000 ml. of distilled water. It is
stored in a glass bottle tightly.
2. Sodium hydroxide.
Dissolve 20 + 0.5 gms o f A.R. quality sodium hydroxide in distilled water. Cool
and dilute to 2000 ml.
3. Buffer Reagent.
Pippete out 25ml of phenol solution into a dry beaker and add 25 ml of sodium
hydroxide solution. The solution is stable for one hour.
4. Copper sulphate solution.
Dissolve 0.1 gm of A JL copper sulphate in 1000 ml of distilled water.
5. Hydrazine sulphate solution.
Dissolve 14.5 gm of A.R. quality hydrazine sulphate in 2000ml of distilled water.
Store in a dark glass bottle. The solution is stable for one month.
6. Reducing Agent.
Mix 25ml o f copper sulphate solution and 25ml of hydrazine sulphate solution in
50 ml measuring cylinder. The solution is stable for one hour.
7. Acetone.
XJ. w t i a u i i i i v i C '
Dissolve 5 gm of sulphanilamide in a mixture of 50 ml con. hydrochloric acid and
about 300 ml distilled water. Diluted to 500 ml with water. It is stable for many
months.
9. N I -N a p h th y l E th y len e D iam ine D i-h y d ro c h io r id e so lu tion (N .N .E .D )
Dissolve 0.5 gm of N.N.E.D. is 500 ml distilled water. Store the solution in a dark
bottle.
10. Standard Niu^te solution
Dissolve 1.53 gm of analytical reagent quality potassium nitrate in 1000 ml.
lml=15.0 ug. at / nitrogen. Dilute 5ml of this solution to 250 ml with water. It is
stored in dark bottle.
Procedure
Measure out 50 ml of the sea water sample with a 50ml measuring cyliner into a
250 cc conical flask, when (sample should acquired room temperature). And 2 ml
buffer reagent and mix. After the buffer has been added to all teh samples, add with
rapid mixing 1.0 ml of reducing agent and keep the flasks away from sunlight in a
dark place for about 20 hours. Add 2 ml of acetone, and after 2 minutes add 1 ml of
sulphanilamide solution. After 2 minutes, but not later than 8 minutes add 1.0 ml of
NJ^^-EX> solution and mix. — ^ J ^
Statistical Analysis:
Statistical analysis o f the data was done using Carl Pearson 's correlation
coeff ic ien t C orre la tion analysis was p e rfo rm ed for d ifferen t w ater quality
Experimental set up
param eters and ciliate prevalence and abundance; and between the water quality
p a ra m e te r s . W h erev er s ign if ican t co rre la tions w ere obse rved , reg ress ion
a n a ly s i s w as done. T h e va lues o b ta in ed w ere a n a ly se d fo r the tes t o f
s i g n i f i c a n c e ^ ^
Laboratory Experiment:
J ^ •••<«» 1 ^ ^ ^ 1 « « •‘V » ^ r\ 9 9% rt ✓v •-» f W >vVf U i i t l W 4 < W I 44 V *A a k V / &« \ y * K V A A W
occurrence o f ciliates on M.dobsoni an experim ent was conducted for a period
of 10 days com m ensing from 9"* to 19‘- June 1997. About 120 M.dobsoni o f
the s ize g roup 30-60m m w ere selected for the experiment. P rio r to experiment,
30 anim als each were acclimatized to the different salinity conditions o f IBppt,
20ppt and SOppt.
A nim als were s tocked in four 60itr fibre glass tanks.^30 animals each
were kep t at 13, 20 and 30ppi salinity conditions for a period o f 10 days. They
-Dwere g iven 50% w ater exchange per day except the tank with deteriorating
water quality. Clam m eat was given ad libitum as food for these prawnsTduring
the period o f the experim ent. Excreta as well as uneaten food w'ere rem oved
by syphon ing . The tank with deteriorating w ater quality, kept at 20ppt salinity
was also stocked with 30prawns. All the tanks were given very good aeration
through ou t this experim ental period.
F ive praw ns each w ere sampled with 2days interval from all the four
tanks tow ards the end o f the experim ental period. The length and sex o f the
prawn, prevalence and abundance of infestation in different salinity conditions
w ere ca lcu la ted as m entioned earlier.
Zoothaiinn ium sp, sind^Vorticella sp. a ITac h e d on to the gi 1 l“f i 1 aments ^ SI
■Ifc-.
RESULT
V- 'r
Estuarine^,Bnvironment:
^ D uring June 1997, water temperature in the culture pond ranged from
,^^^f^0-34°C, salinity 13.4-25.4 ppt, d issolved oxygen 2.8-7.6 ml per Itr, total
suspended soiys(r .s .s) 49-226 mg per Itr, pH 7.5-8.0, phosphate 12.0-30.V^g.
at/ltr and nitrate 1.35 -2.03il g.at/itr (Table -1). These valuer did not v a r y
sign it ican tiy from surface to bottom as the depth was less than Im in the pond.
The m ean values o f salinity, d issolved oxygen andT s.s . w ere 20.2 ppt, 5.2ml
per Itr and 136 mg per Itr respectively, w hile those of phosphate and nitrate
concen tra tions were 20.5 |ig .at/Itr and 1 .7^g.at/ltr respectively in the culture
ecosystem .
C i l ia te O c c u r re n c e in M etapenaeus dobsoni
The ciliate population noticed in the gills of M.dobsoni consisted the
g ro u p s o f Z oo th a m n ium (8 1 % ), A c in e ta { l6 .9 % ), Vorticella(2% ), and
Epistylis(0 .1% ) in th e i r o rd e r o f a b u n d an ce (Plate rv&v) A total o f 101
specim ens o f M.dobsoni were exam ined. The size of the praw n M. dobsoni
ranged from 31-90 mm. The occurrence o f ciliates in the different size groups
o f M .dobsoni in the culture pond is given is table-2. The exam ination of ciliates
in the size groups o f M. dobsoni did not show any size group preference by
the c i lia tes . In the over all prawn population o f culture pond, the m ean values
showed that the ciliates where more abundant in the size group o f 31-40 mm,
" 51 -60mm and 81-90mm and very less in the size group o f 61-70m m (Table -
3). H ighest mean values o f abundance in the population w ere observed in the
size group o f 81-90m m in the present investigation.
A m ong the infested prawns the size group o f 51-60m m w ere found to be
infested m ore with ciliates and less abundance o f ciliates was recorded for the
size group o f 71-80m m ‘(Table -4)
HYDRO GRAPHIC FEATU^S OF THE PRAWN CULTURE POND AT PUTHI^EYPPU - IN JUNE 1997
s \ '
Date
2/6
Temperature (°C)
33
4/6 34
9/6 34
17/6 32
23/6 30
Mean 33
Salinity
(PPt)
22.4
25.4
18.7
13.4
21
20.2
Disslo^ed oxygen (ml / 1)
5.3
6.6
2.8
7.6
3.5
5.SI
Total S u sp e nded solids
(mg/l)
48.8
112.0^"
203.2
91.2
226.0
136.0
pH of Sediment
7.5
PO4( lg•at./l)
20.3
7.5 30.7
7.5 27.5
8.0 12.2
7.5 12.0
N03 (M9- at./l)
2,03
11.7
1,75
1.73
1.35
7.6 20.53 1.7
PREVALENCE O F CILIATE INFESTATION AMONG DIFFERENT SIZE GROUPS OF PRAWN
M. dobsoni.
Size group ( m. m)
No. of Specimens analysed
No. of infested specimens
Prevalence(%)
31 -40 7 4 57.1
41-50 36 11 30.5
51 -6 0 26 4 15.4
61 -70 14 2 14.3
71 -80 10 4 40.0
81 -9 0 8 3 37.5
TABLE - 3ABUNDANCE OF CILIATE INFESTATION AMONG DIFFERENT SIZE GROUPS OF PRAWN -
M. dobsoni in the population.
Size group ( m m)
No. of Specimen's analysed
No. of ciliates (Total)
Average intensity of infestation / specimen s
the population.
31 -4 0 7 19 2.71
41-50 36 71 1.97
51 -60 26 8 0.57
61 -70 14 12 1.20
71 -801
10 26 1.20
81 -90 8 26
101 206
no
ABUNDANCE OF CILIATE AND ITS DISTRIBUTION AMONG D I F F E R E N T S IZ E G R O U P S O F IN
FESTED PRAWNS - M. dobsoni.
Size group ( m m)
No. of infested specimen
No. of ciliatns (Total)
No. of ciliates per specimens or
Ab undance
31 -40 4 19 4.75
41-50 11 71 6.45
51 -60 4 70 17.50
61 -70 2 8 4.00
71 - 80 4 12 3.00
1' 81-90 3 26 B.67
oc
9o>
couoQ.
FIGURE • 1D I S T I ^ I B U T I O N O F C I L I A T E S _ g i i T H E _ O ; n JJ, L _
[ JjAiiluflor Uiii
[[iijMuJJlo Qill
^ I'uiioftof yiil
f im
m
'x'u'-fp
Mfe:
1 p t 20 p p I 3 Op p <Natural coiidilioi
The result o f experim ents conducted in the laboratory for 10 days to
study the salinity preference o f the ciliates at 13, 20 and 30 ppt are given in
table-5. The results showed that the intensity of ciliate infestation xnM.dobsoni
at 30 pp t was high in the popula tion in general and among infested animals
(Table-5).
T 'K rv o V ra rv> t ■' n /-♦ t o <• J t/-v «’ t n /-J » » t K o I <->/-> o #» r \ r> r \ t / - « i l i o t c » C '
in the anterior, middle and posterior gills o f M.dobsoni at 13, 20 and30 ppt
sa lin ity under laboratory cond it ions show ed that the posterior gills were
concen tra ted with ciliates than the m iddle and anterior gills (Table-6). The
observation o f prawns in the natural condition o f pond showed their preference
to pos te r io r gills. The data also show ed that the number o f infested prawns
were re la t ive ly more in the laboratory reared conditions as compared to the
pond ecosystem .
T he ciliate prevalence and abundance on M.dobsoni in the pond showed
positive corre la tion with turbidity (r = +0 .4706 and r = 0.3358 respectively).
W ith th e d is so lv e d o x y g e n o f pond w a te r , abundance (r = -0 .756) and
p revalence (r = -0.68) show ed negative corre la tion , but not to any significant
levels. W hen correlations w ere tried in be tw een water quality parameters, it
was obse rved that tem pera ture and d . o . , T . s . s . and d .o . ,T . s . s . and nitrate are
negatively related w herejis temperature and phosphate, temperature and nitrate
show ed a positive trend.
In the experim ent conducted to find ou t the role o f deteriorating water
quality o i^ the occurieice o f cilia te infestation , it was found that as the water
quality^ecom es badT^uttorians - Acineta sp appear in the culture tank (tables 7).
SALINITY PREFERENCE AND INFESTATION RATE OF CILIATES PER GILL OF M. DOBSONI [EXPERIMENT DATE 9 -1 9 JUNE 1997]
Salinity of the medium
No, of Prawns examined
No. of infested prawns No. of ciliates noticed
Mean intensity of infestation
per animal ( in total)
Mean intesnity per intested
animat
number % prevalence
13ppt 15 11 73.1 127 8.47 11.54
20ppt 14 8 57.3 105 7.50 13.12
30ppt 15 11 73.1 238 15.87 21.64
TABLE-6
OCCURRENCE AND AREA PREFERENCE OF CILIATE INFESTATION ON THE GILLS OFAf. dobsoni [DURING JUNE -1997]
Salinity of the medium
No. of Prawns examined
No. of infested prawns No. of ciliates observed
number % prevalence Ant^icfTigills
Middlegills
Posteriorgills
13 ppt 15 11 73.1 12 17 98>•h->P0.< 20 ppt 14 8 57.3 16 20 69o
z
30 ppt 15 11 73.1 57 52 129
UJcco 1 3 -2 5 101 29 28.7 2 1 73
K<
ppt
zz
T ab le 7 s h o w in g th e e f f e c t o f w a te r q u a l i ty o n th e a p p e a r a n c e o f su c to -
r ian A c in e ta sp. in M .d o b so n i to w a rd s th e e n d o f th e e x p e r im e n t
(E x p t . d a te - 9 to 19 Ju n e )
T K t iA lM E N T F K b h H K h iN (Jb (% )
Zooihamniutn sp. Vorticella sp. Acineta sp.
0 0 0
C o n t r o l6 0 4 0 0
2 0 2 0 0
6 0 0 0
N o w a te r c h a n g e =0 0 r-.
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Ciliate« concentrated on to the anterior free tip of the QJ-iJ
DISCUSSTON
T he d eve lopm en t o f experim ental and com m ercial culture of penaeid
p raw ns has been accom panied by the occurrence of diseases o f infectious and
non-in fec tious e tio logies. A m ong the m ore serious diseases are those caused
by non-in fec tious ep icom m ensal organisms.
in m e p rcscn i i n v c s i i g a i i o n e p i c o m i u e n ^ a i i c ciiiate
in festa tion varied from 0 - 58% in the pond. Gills o f infested prawns when
exain ineu uimei the m icroscope revealed the presence of a large aiimber of
d ic h o to m o u s ly b ra n c h in g co lo n ies o f Zootham nium sp w ith occas iona l
p revalence o f Vorticella sp, Acineta sp and Epistylis sp. Zoothamnium sp
(m ore th an 80% ) w as the m ost p reva len t through out the period of study.
O verstreet, 1973; J o h n s o n ,1973; L ightner, 1975; Couch, 1978; Foster et al.,
1978 o b se rv ed that am ong the different species of ciliates found associated
with sh r im ps the m ost consp icuous is Zoafhamnium. The study conducted byf. - ' '
S a n th a k u m a r i and G o p a la n (1980)^ on’ the es tuarine shrim p Metapenaeus
monoceros and the tena idacean Apseudes chilkensis from cochin backwaters
revealed tha t o f the d if fe ren t species o f ectocom m ensalic cilites, the heaviest
infestation was that o f Zoothamnium. T he protozoan epib iont Zoothamnium
has been reported to p referen tia ly located on the gill lam ellae o f shrimps while
o ther p ro to zo an ep ib ion t do not show site specific ity (Hall, unpublished data).
S talked peritrich Zoothamnium sp, Vorticella sp, Epistylis sp are generally
found a ttached to the gills , appendages and body surfaces (Overstreet, 1973,
1978). Soni (1986) reported mortality due to heavy infestation o f Zoothamnium
sp in the cu ltu re pond at Valappu (Cochin , Kerala).
R e la tive ly h igher concentra tion o f c i lia tes were observed on the anterior
body parts o f the p raw n such as rostrum, carapace and gills. Dense growth of
larger co lon ies o f c i l ia tes w ere observed on the gills (m ore than 90%) through
out the per iod o f study. C oncentra tion o f m ore ciliates at the anterior part of
Ciliates (’ oothawniusi sp 1/orticeiia sp.) attached to thepleopod of prawn iH dobsorr i > ^ o
Photograph showing the superficial attachment of Acineta sp.
; on to the gi 11-1 ame 11 a©
■ -f;
t *
A r
the body o f the host m ight be due to the need for taking advantage of the
resp ira to ry cu rren t o f the host for food and respiration (Santhakum ari and
G opaian , 1980).
A ttachm en t of the c ilia tes on to the body parts o f the prawn does not
appear to cause any m echan ica l dam age to the host tissue as the attachment
was found to be only superfic ia l. About 22% o f the sample (n=238) ofPenaeus
aztecus and P.setiferus from G u lf o f M exico carried suctorian (Ephelota sp)
but they did not appear to cause any histo logical damage (Fontaine, 1985).
W h en the p reva lence o f the ciliate infestation among the different size
g roups w ere analysed , it w as found that, in general ciliates do not show any
size sp ec if ic i ty for the p raw ns. However, the present observation showed that
the ch a n c e s o f be ing in fes ted is relatively m ore for sm aller sized prawns o f ^
the size g roup 31-40 m m . O verstreet (1973) also observed high infestation
rate in sm all sized b row n shrim p.
W hen the c il ia te ab u n d an ce in the w hole population was worked out it
was o b se rv ed that ab u n d an ce is very less for prawn samples of size group 61-
70m m . C ilia tes w ere found m ore abundant among prawn population of size
g roup 31 -40m m 5 1 -60m m and 81 -90mm in the present investigation. But when
the m ean in tensity o f in fes ta tion per infested prawns were calculated, it clearly
ind ica ted the size p re fe ren ce o f the cilia tes to prawns samples of 51-60mm
size. T h a t m eans, once in fes ted by ciliates, the number o f ciliates increase in
c o n s id e rab le num bers in this size group. O ut o f the 4 praw ns examined o f this
s iz e g ro u p (5 1 -6 0 m m ) a b o u t 70 c i l ia te s w ere observed , ind ica ting the ir
m ax im u m abundance in this s ize group.
T h e num ber o f c i l ia tes should correlate with quality of the water and
in d ic a te th e c o n d i t io n s th a t are su i ta b le fo r bac ter ia , p a r t icu la r ly those
associa ted with e levated organic matter and other nutrients in the pond (Couch.
1983). Cultu re practices often provides those exact conditions that is, the
abundance o f substrate (host - cuticular surface) and concentrated bacterial
popu la tions due to organic wastes.
W hen the various w ater quality parameters were analysed, it was observed
th a t d is s o lv e d o x y g en (§ ).^ value f lu c tu a te d be tw een 2 .8 -7 .6m l p e r Itr
( 1 UUlC i ). I iiw . vctiuc liiuiuatcS plauiCiuriiC bloOiV* ;**i tho
V npond. There were 2 alternate peaks and drops in th e ^ ^ e . values indicating
p lank ton ic bloom and die off. The first peak is soon followed by a fall in the
value as the p lankton die. It takes some time for the d.6. value to rise
again as the algal scum formed from algal die off will deteriorate the w ater
quality making the conditions unfavourable for the grow th o f plankton. The
second peak values of d.o. which is the m axim um value recorded, is observed
as the algae blooms again. The death o f algal bloom again brings dow n the
d.o. value. The supersaturation of d.o. values in the culture pond observed on
2 occasions in June (4 ‘*' and 17“') could be more likely due to the excess
b loom ing of photosynthetic phytoplankters. This has p robably led to the
subsequent reduction o f oxygen values to a low level in few days causing an
unhealthy environm ent, m ore likely by the death of the short lived photo
synthetic organisms which has resulted in the increase of total suspended solids
tr s .s .) values. The rate o f decomposition o f plant materials are increased if
p ro tozoans are present to graze the bacteria (Mann, 1982). The low values o f
d.o. indicates a reduction in the photo synthetic activity o f the planktons,
c o n s u m p t io n o f o x y g e n by o rgan ic m a t te r c o n tr ib u te d by p la n k to n ic
decom position and respiration by benthic organisms including prawns. So as
th e p la n k to n b e c o m e m o re ab u n d an t , r a te o f o x y g e n p r o d u c t io n and
consum ption increases (Boyd, 1985).
A bundance and prevalence of ciliate infestation is found to be much
related to the d.o. content o f the water. Johnson er a/., (1973) reported mortality
o f p o n d held shrimps due to the presence o f large number o f Zoothamnium on
28
the gills and a reduction in the oxygen levels. Death of prawn due to heavy
i n f e s t a t i o n o f Z o o th a m n iu m u s u a l ly c o in c id e s w ith p e r io d s o f lo w
concen tra t ions of drO. in the water, a com m on condition following several
w a rm o v e rc a s t days or fo l lo w in g d e c o m p o s i t io n o f large algal b lo o m s
(O vers tree t, 1975). Soni (1986) reported mortality of penaeid shrimps due ton
heavy infesta tion ot'Zoothamnium when the d.o. level was as low as 2.36 ppm.
R ela tive ly high correlation was obta ined between d.o. andT 's.s., m ore
likely due to plankton die o ff M ax im um T s.s values were recorded
when the d.o. values showed a decline (table 1). TS'.^ peaks were soon followedQt>
by d .o . peaks , then drop in th e T s . s . w hich indicates t h a t x s . s . is m ain ly
contributed by organic matter produced by algal die off. Brownish colourations
o f the pond water was observed associated with algal die off giving a high
T .s .s . value for the day.
r>oMaximum abundance and prevalence of ciliates were observed when d.o.
values were the lowest. Plankton die off and subsequent putrifaction of the water
makes the situation congenial for the bacterial multiplication in the system. High
T .s .s . v a lu e s a lso rev e a l o rg a n ic d e g ra d a t io n b y b a c te r ia . The i n c re a s e i n T s . s .
values favour|/n the adherence of bacteria more and more in the water medium
which may serve as food for those ciliated protozoans to promote the ciliate
population: in the environment as evidenced by the occurrence of relatively more
num ber o f ciliates on these two days (9* and 23' *} with relatively h ig h er
c o n c e n t r a t i o n (>200mg p e r Itr) o fT s .s . in w a te r . So, as the b a c te r ia l lo ad in c r e a s e s ,
ciliates which feed on bacteria flourish ■ in the system. Peak values for abundance
and prevalence of ciliate infestation obtained under conditions of low d.o. and
h ighT -S .s . Experimental infestation o f Zoothamnium in s h r im p and th e e f f e c t o f
stress produc&tby high turbidity and low d.o. conditions were carried out by
Overstreet (1973) and in tenaidaceans by Santhakumari and Gopalan (1980)
revealed that high turbidity of the medium resultiin fall in the d.o. values which
intorn cause mortality of the population.
29
DISTRIBUTION OF DISSOLVED OXYGEN, TOTAL SUSPENDED SOLID AND OCCURRENCE OF CILIATES
P re v a l e nc e
Toia! ^uSOciidtu so l id s
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D I S T R I B U T I O N O F T E M P E R A T U R E ,
P H O S P H A T E A N D O C C U R R E N C E
O F C IL IA T E S
diurnal variation during the period nf study,*1 V\6t"the param eter is^treated to compare the abundance of the ciliates. Salinity is
found to play little role in cilia te infestation, as infestation was observed both
at high and low salinity conditions.
D u n n g ^ e r i o d o f s tu d y p h o sp h a te va lued varied between 12-30.7.
n g .n f . / I f r^hospha te and nirrate existed in fhe nond water in the ratio o f 12:1
d u r in g the period o f s tudy . B acteria l a c t iv i ty is enhanced by increased
av a i lab i l i ty o f phospha te in the system (M ann, 1982). The occurrence of
phospha te and nitrate in the water throughCout the period o f study indicated
that these nutrients h ow ever do not function as the lim iting factor for the
reduc tion o f photorsynthetic phytoplanktons.
T he experim ent conducted to find out the salinity preference of ciliate\
on M.dobsoni at . d iffe ren t salinity conditions of 13ppt, 20ppt and 30ppt
show ed that infestation is low at 20 ppt salinity than at 13 and 30 ppt salinities.
P reva lence o f cilia te infestation is only 57% at 20ppt w h e r e a s chances of
be ing infested is almost same (73%) at both the salinity e x i t e d ^ (13 and
30ppt). W hen the num ber of ciliates observed at different salinity conditions
o f 13ppt, 20ppt and 30ppt were compared, it was observed that, maximum
num ber o f ciliate w ere observed at 30ppt salinity values. This indicates the
p reference o f ciliate to get multiplied and established at 30ppt salinity, where
as at 20ppt salinity which is considered as the most preferred salinity condition
for M.dobsoni, the num ber of ciliates observed was low. When the m ean
in tensity o f infestation in the population at different salinity conditions were
co m p ared , it was again p r o v e d salinity conditions. Maximum
values for the abundance o f ciliate infestation among infested prawns again
co n f irm ed that salinity around 30ppt is the most preferred salinity condition
for the cilia te accord ing to the present study. Soni (1986) reported ciliate
in fes ta tion at 31.2ppt salinity in Penaeus monodon, PAndicus and Metapenaeus
m onoceros from cochin baclO vaters . H ow ever Santhakumari and Gopalan
(1980) reported increased rate of infestation during m onsoon months as an
ind ication to their prefarence to low salinity conditions. This might be due to
d ifference in the species o f ciliates which are tolerant to the respective salinity
m edium .
W hen the prevalence of ciliate infestation on M.dobsoni under natural
UUJ'iUjUJlU Li]lUci Ciipiivfc COiJUltuiiS WCiC cuiupuitu, ii was cviuciii lliai
preva lence o f ciliate infestation is very low (28.7%) in the month of June in
the natural condition than under conditions of captivity. Out of the 101 samples
analysis , only 29 anim als were found infested by ciliates, where as in the
c a p t iv e co n d i t io n s o f d if fe ren t sa lin ity values (13ppt, 20ppt and 30ppt)
p revalence varied betw een 57-73%. In the natural condition salinity fluctuated
be tw een 13-25ppt. Soni (1986) reported that infestation of ciliates on praw ns
is m odera te during pre-m onsoon (April-June) and rare during other months.
T he hydro g rap h ic fea tures o f the cu ltu re pond in June 1997 prov ided an
env ironm en t o f transition of the pre-monsoon habitat entering into the onset
o f south west m onsoon habitat, with the salinity decreasing from 13-25ppt in
June . This would result in the survival o f certain euryhaline ciliates alone in
the habita t and this could be the probable reason for the occurrence o f less
num ber o f ciliate infestation during the period of study. Couch (1985) also
reported the seasonal prevalence o f ciliate Lagenophrys callinectes in blue
c ra b w h ere he found a d irec t re la t io n sh ip be tw een h igh p re v a le n c e o f
L.callinectes in summer months and high intensity of individual crab infestation
o f L.callinectes. However Santhakumari and Gopalan (1980) reported increased
rate o f infestation during monsoon months.
W hen the loca tion prefarence o f ciliates on the gills both in natural
cond it ion and captive condition were observed, it was found that ciliates are
m ore concentrated on to the posterior gills than in the middle and anterior
gills . T he ir num ber on the anterior and middle gills are rare in the natural
cond it ion of the pond. But in the experimental tanks, ciliates are seen slowly
spreading from the posterior gills towards anterior and middle gills. Fairly
good num ber o f ciliates in the anterior and middle gills indicated that ciliates
prevalence in M.dohsoni preferred higher salinity (figure -1). Experimental
infestation of Zoothamnium in M.monoceros by Santhakumari and Gopalan
(1980) show ed that colonies of ciliates get established on uninfested shrimp
in 3 - 4 d a y s w h e n i n f e s t e d a n im a ls w e re p u t a lo n g w i th u n in f e s t e d
individuals.Relatively high rate of infestation with more dens colonies occurred
on the reared individuals than those co llected from the nature, which shows
the p ro b a b le c o n d u c iv e n e s s o f s ta g n a n t w ate rs and o v er c row ding for
infesta tion (Overstreet, 1973) as it is observed in the present study.
Prevalence o f cilia te infestation M.dohsoni was about 28% in the pond
in the presen t study. The attachment o f the ciliates on to the prawn cuticular
su r fa c e d o e s no t in f l ic t any m e c h a n ic a l dam age to the host , but h igh
encrusta tion o f the ciliates on the gill surface may, reduce the respiratory
surface area o f the prawn, leading to hypoxia and even to severe mortality as
observed by Johnson (1973) and Overstreet (1983). The prevalence o f ciliates
in fes ta t io n under conditions of high to tal suspended so lids and deple ted
d issolved oxygen indicates that the occurrence o f ciliate infestation in prawn
is an indication of deteriorated water quality. It is more likely that some of the
species o f Zoothamnium may serve as indicator of deteriorated water quality.
More studies on this aspect to these species level is desirable.
SUMMARY
Epicom m ensalic protozoans associated with Metapenaeus dobsoni consisted
o f species of Zoothamnium, Vorticella, Epistylis and a suctorian Acineta.
The m ajor observations made in the present study are,
1. The most prevalent ciliate observ^ed was species oiZooth.amniiun (more
than 80%) followed by Ac//ie/a(16.9%), Vorticella {2%), Epistylis{0.l%)
2. The prevalence o f ciliate infestation was comparatively low in M.
dobsoni during June in the estuarine environment (28.7%) ^
3. Infestation was found high in the gills (more than 90%) than in other
external parts o f the body.
4. Intensity of infestation was found high in the prawns of the size group
51-60mm.
5. Ciliates were found to show a preference to get infested in the posterior
gills than on the anterior and middle gills.
6. Correlations were observed between water quality parameters such as
dissolved oxygen and total suspended solids in the pond and ciliate
infestation. It was observed that under conditions of high total suspended
solids and low dissolved oxygen ciliate infestation is high.
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