desarrollo y dinamica poblacional tisbe

Ž .Aquaculture 198 2001 253–267www.elsevier.nlrlocateraqua-online

Development and population dynamics ofTisbež /biminiensis Copepoda: Harpacticoida reared on

different diets

Cristiane S.C. Pintoa, Lılia P. Souza-Santosb,),´Paulo Jorge P. Santosa

a Zoology Department, UniÕersidade Federal de Pernambuco, Cidade UniÕersitaria, CEP 50.670-901,´Recife, Pernambuco, Brazil

b Oceanography Department, UniÕersidade Federal de Pernambuco, Cidade UniÕersitaria, CEP 50.670-901,´Recife, Pernambuco, Brazil

Received 31 July 2000; received in revised form 20 November 2000; accepted 20 November 2000

Abstract

The harpacticoid copepodTisbe biminiensis was reared under controlled laboratory conditions.In order to study the effects of food on larval development and on population dynamics, threediets were tested: the microalgaeNitzschia closterium, Tetraselmis gracilis and a mixture of bothalgae. The life-cycle parameters were measured, and the demographic variables such as generationtime, net reproductive rate, and exponential rate of increase were determined. Results showed thatdiet affected development and fecundity. Larval development was delayed in copepod fedT.gracilis. The mean number of nauplii per brood was significantly greater in copepod fed theN.closterium diet than those fed the other diets. Survival did not differ significantly between

Ž .treatments. The exponential rate of population increaser was greater in copepod fed theN.Ž y1. Ž y1.closterium diet 0.49 day and lower in those fed theT. gracilis diet 0.35 day . The results

showed that althoughTis. biminiensis seemed to be able to develop and reproduce on aT. gracilisdiet, the diatomN. closterium promoted better results for this copepod in terms of development,fecundity and populational growth rates. The short generation time and high reproductive potential

) Corresponding author. Fax:q55-81-3271-8227.Ž .E-mail address: [email protected] L.P. Souza-Santos .

0044-8486r01r$ - see front matterq 2001 Elsevier Science B.V. All rights reserved.Ž .PII: S0044-8486 00 00582-2

( )C.S.C. Pinto et al.rAquaculture 198 2001 253–267254

make the use of this copepod promising as live food in aquaculture.q2001 Elsevier Science B.V.All rights reserved.

Keywords: Harpacticoid copepods; Population dynamics; Development; Diet;Nitzschia closterium; Te-traselmis gracilis

1. Introduction

Many predators go through an obligatory meiofaunal feeding stage, and benthiccopepods appear to be the major meiofauna prey item for most predators of meiofaunaŽ .Coull, 1999 . Copepods are one of the feeding items preferred by juvenile penaeid

Ž .shrimp in nature Dall et al., 1990 , and they usually dominate the gut contents ofŽ .feeding larval fish Hicks and Coull, 1983 . Therefore, copepods are an important link in

the marine food web, and serve as an important food source for many larval and juvenileŽ .fish species Feller and Coull, 1995; McCall and Fleeger, 1995 .

Ž .In aquaculture, Delbare et al. 1996 reported several advantages in the use ofcopepods as live food for marine fish larvae: the wide range of body size betweennauplii and adults; the movement that constitutes a visual stimulus for the larvae; the

Ž .high amounts of polyunsaturated fatty acids PUFA ; the higher levels of digestiveenzymes which may play an important role during larval nutrition and, in the case ofharpacticoid copepods, keeping the tank wall clean by feeding on detritus that developson it.

Ž . Ž .Coull 1999 stated that certain essential fatty acids EFA , particularly the highlyŽ . Ž .unsaturated fatty acids HUFA , specifically eicosapentaenoic acid EPA and the

Ž .docosahexaenoic acid DHA , determine the nutritional value of diets for marine fish,and that the aquaculture industry recognizes the importance of supplementing traditional

Ž .diets with harpacticoid copepods as a source of these EFA Støttrup and Norsker, 1997 .Species of harpacticoid copepods, i.e.Tisbe and Tigriopus, have high levels of EPA

Ž .and DHA Norsker and Støttrup, 1994; Nanton and Castell, 1998; Coull, 1999 , and asŽ .stated by Delbare et al. 1996 , they make promising candidates for mass culture as live

food for fish and crustacean larvae for the following reasons: they have high fecundityand short generation time; they tolerate a wide range of environmental changes; they canuse a large variety of food sources, as rice bran, yeast and algae and reach high

Ž .population density Kahan et al., 1981r1982 .Harpacticoid copepods are able to ingest a wide variety of diets, namely, diatoms,

Ž .phytoflagellates, bacteria, detritus, fungi and yeast Hicks and Coull, 1983 . Tradition-ally, diatoms have been considered one of the most important components of copepodsdiet because diatom frustules are observed more easily within copepod gut contents

Ž .compared to other food items Souza-Santos et al., 1999 . Recent studies have chal-lenged the classical view that copepod production in the ocean is primarily based on

Ž .diatoms Jonasdottir et al., 1998 . Several authors have argued that diatom extracts or a´ ´unialgal diatom diet can be toxic or deleterious to copepods with negative effects on egg

Ž .production and egg hatching success Ban et al., 1997 . However, these observations donot allow one to determine whether the inadequacies of these diatom diets are due to

Ž .toxicity or nutritional insufficiency Jonasdottir et al., 1998 .´ ´

( )C.S.C. Pinto et al.rAquaculture 198 2001 253–267 255

The aim of this study was to describe the development rate and population dynamicsŽ .of Tisbe biminiensis Volkmann-Rocco, 1973 and test the effect of three microalgae

Ž .diets Nitzschia closterium, Tetraselmis gracilis and the mixture of both , on develop-ment, fecundity and survival of this copepod.

2. Materials and methods

2.1. Algal culture

Ž .During this study one species of diatomNitzschia closterium Bacillariophyceae andŽ .one species of flagellateTetraselmis gracilis Prasinophyceae were used. These were

chosen becauseN. closterium has been used with success inTis. biminiensis culture andT. gracilis belongs to a genus that is one of the most widely used in aquaculture for

Ž .feeding marine herbivores Lourenc¸o et al., 1997 . Both microalgae were cultivated inŽ .fr2 medium Guillard, 1975 . During the medium preparation, natural seawater at a

Ž . Ž .salinity of 34‰ was filtered 0.7mm . The Tris–HCl buffer pH 7.8 and fr2 nutrientstocks were added to seawater before medium sterilization in an autoclave. Vitamin

Ž .solution was sterilized by filtration 0.2mm and added to the media just before algalŽ .inoculation. Cultures were incubated at a room temperature 28–308C , with a 12-h

lightrdark photoperiod.Ž .Microalgae concentrations are expressed as units of chlorophylla ng Chl-arml

because the formation of large aggregates hindered cell counts. After an 8-h extractionwith 90% acetone, chlorophylla concentrations were measured spectrophotometrically

Ž .at 665 and 750 nm using the equations of Lorenzen 1967 . Acidification was achievedby addition of 100-ml aliquots of 0.1 N HCl to a sample volume of 3 ml.

2.2. Copepod cultiÕation

The copepod speciesTis. biminiensis was cultured for several generations in 50–500Ž .ml vessels with 0.7mm filtered seawater salinity 34‰ . Cultures were maintained at

28–308C in 12-h darkrlight photoperiods.

2.3. Estimation of optimal food concentration

Two experiments were carried out, one withN. closterium and another withT.gracilis. Egg-bearing females were sampled on maintenance cultures where they werefed N. closterium but without food concentration control. Thirty-five copepod femaleswere placed individually in vessels containing 50 ml of algal suspension of varyingchlorophyll a concentration. Five replicates were used for each chlorophylla concentra-

Ž .tion and control copepods in 0.7mm filtered seawater without food . Six different algalconcentrations were tested. Vessels were incubated for 24 h under the same conditionsas copepod cultures. At the end of the incubation period and after checking for copepodsurvival, the vessel contents were preserved in 4% vrv formalin for further analysis.The number of fecal pellets produced by each copepod was counted under a stereo-mi-croscope. To estimate the total volume of fecal pellets produced, the length and width of


20 pellets for each food concentration were measured using the methods of Souza-SantosŽ .et al. 1995 .

2.4. DeÕelopment rate and population dynamics of Tis. biminiensis reared on N.cloterium and T. gracilis cultures

At the start of the experiment, 45 egg-bearing females were separated from themaintenance culture. Each group with 15 females was fed different diets, one groupreceived N. closterium, another group receivedT. gracilis, while the third groupreceived a 1:1 mixture of both microalgae. The chlorophylla concentration used was100 ng Chl-arml for the three treatments. Twelve hours later, 40 hatched nauplii from

Ž .each treatment were placed individually in cavities 0.3 ml of sterile multi-well platescontaining food suspension. To reduce evaporation, wells situated at the border of themulti-well plates were filled with distilled water and multi-well plates were placedinside covered plastic trays.

Once the copepodite stage was reached, animals from the same treatment werecombined in glass vessels containing 50 ml of the treatment diet. During copepoditestages, cast exoskeletons were removed every 6 h, preserved in 4% vrv formalin andstained with Rose Bengal. During naupliar development, there were no food additions.Only when the copepodites were placed in 50-ml vessels was the food renewed. Afterlaying the first egg sac, each female was isolated in a glass vessel containing 50 ml ofthe treatment diet. When the new brood hatched, females were transferred to a newvessel and the nauplii released preserved in 4% vrv formalin and stained with RoseBengal.

Segments of cast exosketetons were counted under a microscope to determinecopepodite stage. Length of each cast exoskeleton, from end of cephalothorax to caudalrami, was measured under a microscope.

2.5. Statistical analysis

Simple linear regression analysis was used between development stages and develop-ment time, and between development stages and animal size. Regression line slopeswere compared using 95% confidence intervals. If the lines were parallel, the elevations

Ž .were compared using the covariance analysis ANCOVA .Life tables based on 1-day intervals were constructed for each group maintained

Žunder different treatments. The female age-specific survivall , the proportion ofx. Žfemales surviving to agex and age-specific fecunditym , mean number of femalex

.nauplii born per day and per female of agex were used to calculate differentlife-history parameters, using a Populus 3.4 program.

Means were compared using two-way ANOVA after testing for the data normalityŽ . Ž .Kolmogorov–Smirnof test and the variance homogeneity Bartlett test . The non-para-metric test of Kruskal–Wallis was used if the data were not normal or variances werenot homogeneous. The Tukey test was used to identify significant differences between

Ž . Ž .treatment means pairwise comparisons . The binomial test Zar, 1999 was used to test


whether observed sex-ratios of each replicate differed from equality. The significancelevel in this case was 0.05.

3. Results

3.1. Estimation of optimal food concentration

Tis. biminiensis in controls produced less than one fecal pellet in 24 h. When fedN.closterium, the number of fecal pellets produced was significantly different among algal

Ž .concentrations ANOVA,Fs15.16, P-0.0001 . At algal concentrations from 9.1 to73 ng Chl-arml, the number of fecal pellets increased significantly, and from 73 ng

Ž .Chl-arml onwards the production was rather constant Fig. 1a . There was a significantŽ .variation of fecal pellet volume ANOVA,Fs4.07, Ps0.0037 ; there was a decrease

at a concentration of 37 ng Chl-arml and from 73 ng Chl-arml onwards there was astabilization. When fedT. gracilis, the number of pellets produced was not significantly

Ž .different ANOVA, Fs2.44, Ps0.067 . However, at concentrations from 11 to 92 ngŽ .Chl-arml, the number of pellets increased Fig. 1b . There was a significant variation of

Ž .fecal pellet volume ANOVA,Fs7.02, P-0.0001 ; there was a decrease at 23 ngChl-arml and a stabilization from 185 ng Chl-arml onwards.

3.2. DeÕelopment time and growth in size of Tis. biminiensis

Significant linear relationships were identified between development stages andŽ .development time in the three diets Fig. 2a . The regression line slope of theT. gracilis

diet was significantly higher than the other diets. Regression lines of theN. closteriumŽand the mixed diet were parallel, but elevations were significantly different ANCOVA,

.Fs19.2, Ps0.0018 . Total development time of copepods was significantly influ-Ž . Ženced by diet type ANOVA,Fs233, P-0.0001 and sex ANOVA,Fs60.3,

. ŽP-0.0001 . A significant interaction between diets and sex was also observed ANOVA,. Ž .Fs11.5, P-0.0001 Fig. 3a . Usually, the total development time was longer in

females than in males, except for theN. closterium diet where both sexes had the samedevelopment time . The total development times increased from theN. closterium dietto theT. gracilis diet.

Significant linear relationships were observed between development stage and bodyŽ .size in the three diets Fig. 2b . The regression lines were not significantly different

Ž . Žbetween diets ANCOVA,Fs0.609, Ps0.56 . Both sex ANOVA, Fs484.4,. Ž .P-0.0001 and diet ANOVA,Fs14.2, P-0.0001 influenced the body size. A

Ž .significant interaction between treatments and sex ANOVA,Fs12.7, P-0.0001Ž .was also observed Fig. 3b . Females were larger than males in the three diets. Females

fed N. closterium were smaller than those fed the other diets. The development time andŽ .the D rD ratio of total copepodite to total naupliar development time decreased fromc n

Ž .the T. gracilis treatment to theN. closterium treatment Table 1 .

3.3. Population dynamics

Ž .The age of the first reproduction Table 1 was significantly greater in copepods fedŽthe T. gracilis diet and theT. gracilisqN. closterium mixture ANOVA, Fs61,


Ž y1 y1.Fig. 1. Mean number of fecal pellets produced fecal pellets cop day and mean fecal pellet volumeŽ 3. Ž . Ž .=0.0001 mm ofTisbe biminiensis in relation to microalgae concentration ng Chl-arml ; a Nitzschia

Ž . Ž .closterium and b Tetraselmis gracilis. Vertical bars denote the confidence intervals of the meansPs0.05 .Ž .The same letters indicate means which do not differ significantly Tukey test and ANOVA .


Ž . Ž . Ž . Ž .Fig. 2. Regression lines between copepodite stages and development time h a and body sizemm b ofŽ . Ž .Tis. biminiensis fed the N. closterium traced line ,N. closteriumqT. gracilis dotted line andT. gracilis

Ž .diets solid line .

. Ž .dfs2r32, P-0.0001 . Larval survival was high in all three treatments Table 1 . TheŽ . Žreproductive period was similar among treatments Table 1 ANOVA,Fs0.266,


Ž . Ž . Ž . Ž .Fig. 3. Variation of body sizemm a and development time h b ofTis. biminiensis as a function of sexŽ .and diet. Vertical bars denote the confidence intervals of the meansPs0.05 .

.dfs2r32, Ps0.768 . The mean number of broods produced during the reproductiveŽperiod was not significantly different among treatments Kruskall–Wallis,Hs3.79,


Table 1Duration of life-cycle stages ofTisbe biminiensis fed Nitzschia closterium, Tetraselmis gracilis and N.closteriumqT. gracilis diets

N. closterium T. gracilis N. closteriumqT. gracilis

Time spent as nauplius 2.05 2.61 2.34Total development time 4.25 6.59 4.97D rD 1.07 1.52 1.12c n

Age at maturity 4.2 6.5 4.9Ž .Survival to maturity % 93 97 92

b a aAge at first brood 7.6"0.5 10.8"0.9 10"0.0ns8 ns16 ns9

a a aReproductive period 14.6"2.4 15.3"2.2 15.3"2.4ns8 ns16 ns9

a a aPost-reproductive period 7.7"6.1 7.8"4.3 8.4"3.1ns8 ns16 ns9

a a aFemale lifespan 29"7.2 32.9"4.9 32.7"4.6ns8 ns16 ns9

a a bMale lifespan 29.4"7.9 26.6"8.0 17.9"4.1ns27 ns16 ns9

Ž .Time is given in days means"S.D. . D rD represents the ratio of total copepodite to total naupliarc n

development time. The same superscripts in the same row indicate means which do not differ significantlyŽ .Tukey test and ANOVA,Ps0.05 .

. Ž .Ps0.15 Table 2 . One female may produce up to nine broods during its life. Themean number of nauplii per brood was significantly greater in theN. closterium

Ž . Žtreatment than the other treatments ANOVA,Fs20.8, dfs2r32, P-0.0001 Table.2 . The number of nauplii decreased with brood number. Often, the nauplii hatched from

egg-sacs still attached to females. Females laid a new egg-sac 2 days after nauplii wereborn. The post-reproductive period was not significantly different among treatmentsŽ . Ž .Kruskall–Wallis, Hs0.08, Ps0.96 Table 1 .

Table 2Reproductive parameters ofTis. biminiensis fed N. closterium, T. gracilis and N. closteriumqT. gracilisdiets


Total no. of broods 54 104 68a a aNo. of broodrfemale 6.8"1.3 6.4"0.8 7.3"1.2

ns8 ns16 ns9a b bNo. of eggsrbrood 69.0"24.6 40.6q16.1 46"17.1a b bNo. naupliirbrood 66.8"28.5 39.6"17.6 44.8"19.9

ŽMeans"S.D. The same superscripts in the same row indicate means which do not differ significantly Tukey.test and ANOVA,Ps0.05 .


Ž .Lifespan of females was not significantly different among treatments Fig. 4Ž .Kruskall–Wallis, Hs1.11, Ps0.57 . Lifespan of males was shorter in the mixed diet

Ž . Ž . Ž . ŽFig. 4. Age-specific survival percentage of maleB and female ' and age-specific fecundity mean. Ž . Ž .number of female nauplii born per day per female of agex v of Tis. biminiensis fed the N. closterium a ,

Ž . Ž .N. closteriumqT. gracilis b andT. gracilis diets c .


Ž .Fig. 4 continued .

Ž . Ž .fed group ANOVA, Fs18.4, dfs2r70, P-0.0001 Table 1 . Female lifespan wasgreater than male lifespan in the mixed treatment and similar in the other treatmentsŽ .Table 1 .

Ž .Sex ratios observed for copepods fed withN. closterium 25% of females andN.Ž .closteriumqT. gracilis 29% of females were significantly different from 50%. The

Ž .sex ratio observed for theT. gracilis treatment 42% of females was not significantlyŽ .different from 50% binomial test,ns32–38 . In theT. gracilis treatment, the net

reproductive rate was greater than the other treatments, but generation time was longer,Ž .resulting in a lower exponential rate of increase Table 3 .

Table 3Life-history parameters ofTis. biminiensis reared at 28–308C, 34‰ of salinity and fedN. closterium, T.gracilis and N. closteriumqT. gracilis diets


Ž .R net reproductive rate 95.7 113.4 78.3oŽ .r exponential rate of increase 0.49 0.35 0.35

Ž .daysŽ . Ž .T generation time days 12.2 15.9 14.9

yr x ŽR sSl m , Sl m e s1 andTs ln R r r, where l is the age-specific survival proportion of femaleso x x x x o x. Žsurviving to agex and m is the age-specific fecundity mean number of female nauplii born per day and perx

.female of agex .


4. Discussion

The relationship between the number of fecal pellets produced byTis. biminiensisand the food concentration followed the expected models where the ingestion rateinitially increases with food concentration up to the optimal or critical concentration, anddoes not change anymore with the increase of food concentration. Therefore, it can besuggested that the critical levels ofN. closterium andT. gracilis to feedTis. biminiensiswere 73 and 92 ng Chl-arml, respectively. However, as a function of high individualvariability, the number of fecal pellets produced by copepods fed withT. gracilis did notvary significantly among algal concentrations. It is also important to note that at theseconcentrations, copepods produced 100 pellets per day. It is difficult to accuratelycompare the critical food concentrations between species of copepods since for each

Ž .study different algal species were used. Souza-Santos 1996 showed that the criticallevels of Nitzschia sp. andN. constricta for Amonardia normani were 300 and 130 ngChl-arml, respectively, and suggested that food availability of the copepod habitatgoverns the optimal food level.

Development time ofTis. biminiensis was shorter in theN. closterium treatment andŽ .longer in theT. gracilis treatment Fig. 3a . AlthoughT. gracilis seemed to be sufficient

for complete development, these results show the importance of diatoms in the diet ofthis copepod. Development rates are also strongly affected by temperature, quantity, and

Ž . Ž .quality of food Hicks and Coull, 1983 . Williams and Jones 1994 showed that foodlimitation had a pronounced effect on postembryonic development ofTis. battagliai andprolonged stage duration was observed at relatively high algal concentrations. This may

Ž .be due partly to potential nutritional deficiencies of this unialgal diet. Guidi 1984observed that the development rate ofTis. cucumarie was also affected by the type offood offered. In the current study, it was verified that male development time wasshorter than female development time in animals fed the three diets tested. Developmenttime of both males and females was delayed in copepods fed withT. gracilis.

Sexual dimorphism in size has been noted for many harpacticoids where adultfemales tend to be larger than males. The ecological significance of sexual dimorphismcould be manifold, such as for sex recognition or for reduction of intraspecific

Ž .competition for food sources Lee et al., 1985 . Food, temperature and biotope mayŽinfluence not only development rate, but also the final size reached by copepods Hicks

.and Coull, 1983 . Female body size ofTis. biminiensis was larger than males in theŽ .three treatment groups. Only female body size was affected by treatments Fig. 3 , the

short size attained by animals fed withN. closterium may be a result of the fasterdevelopment time observed in this treatment.

An extensive review of postembryonic duration of copepods was provided by HartŽ .1990 who suggested that theD rD ratio might provide a useful and simple index ofc n

Ž .food availability during development. Hart 1990 showed, with few exceptions, that theenhancement of naupliar development with increasing food supply was far less pro-nounced than the corresponding acceleration of copepodite development over equivalentfood increases. Therefore, theD rD ratio decreased with increasing food availability.c n

Ž .Souza-Santos et al. 1999 suggested that theD rD ratios can also be used as anc n

indicator of food quality as well as food quantity. In the current study, theD rD ratioc n


was positively correlated to total development time of copepods, supporting this recenthypothesis.

Fecundity of Tis. biminiensis was affected by diet. Best results of fecundity wereachieved by copepods feedingN. closterium. The mean number of nauplii produced ineach brood was higher in copepods fed theN. closterium diet than in those fed the otherdiets, although the number of broods was similar. Different food types appear to elicitdifferent reproductive responses but the specific components of the diet responsible for

Ž .these differences have not been fully identified Williams and Jones, 1999 . Theinfluence of diet on the reproductive parameters ofTisbe spp. cultured in the laboratory

Ž .has been investigated by several authors. ForTis. furcata Abu-Rezq et al., 1997 andŽ .Tis. carolinensis Lee et al., 1985 best results were achieved when copepods were fed

diatoms, leading both authors to suggest that this may be associated with the highŽ .nutritional value of diatom. Miliou and Moraitou-Apostolopoulou 1991 noticed that the

reproductive performance ofTis. holothuriae was more efficient when fed a mixed dietŽof seaweedUlÕa sp. and Fryfood a commercial product containing animal and

.vegetable components and enriched with unsaturated fatty acids than a diet with a lowfatty acid content such asSpirulina.

Survival of Tis. biminiensis females was not affected by diet. Male survival was shortŽ .for those fed the mixed diet. Abu-Rezq et al. 1997 suggested that the low energy

gained by Tis. furcata females fed thePaÕloÕa lutheri flagellate diet may haveŽ .contributed to its short lifespan. By contrast, Nilsson 1987 observed that the average

lifespan and the reproductive period ofA. normani were not significantly affected bydifferent diets. Survival ofTis. biminiensis to adulthood was high in the three treatment

Žgroups, and was similar to data obtained for otherTisbe species Bergmans, 1981;. ŽWilliams and Jones, 1994 and forA. normani Nilsson, 1987; Souza-Santos et al.,

.1999 .Ž .The values of the exponential rate of increaser obtained for groups fed with the

Ž .three diets Table 3 showed the greater importance of the generation time overfecundity rates. These results showed that althoughTis. biminiensis seemed to be able todevelop and reproduce when fed theT. gracilis diet, the diatomN. closterium promotedbetter results for this copepod in terms of development, fecundity and populationalgrowth rates. This may be due to potential nutritional deficiencies of theT. gracilis diet.The nutritional value of microalgae is linked to its biochemical composition, and thisnutritional value is related to the nutritional needs of the animals cultured on itŽ . Ž .Mourente et al., 1995 . The highly unsaturated fatty acids HUFA , such as eicosa-

Ž . Ž .pentaenoic acid EPA and docosahexaenoic acid DHA , are believed to be synthesizedde novo in sufficient quantities only by photosynthetic organisms, and have therefore

Ž .been considered essential dietary nutrients for marine copepods Fraser, 1989 . RenaudŽ .et al. 1994 highlighted the diatomN. closterium as having high percentages of lipid

and the polyunsaturated fatty acids EPA and DHA. The genusTetraselmis showedŽ .moderate amounts of EPA and little DHA Renauld et al., 1999; Thinh et al., 1999 .

Ž .Lourenco et al. 1997 reported the absence of DHA as well as low concentrations ofEPA in T. gracilis.

Although several authors have argued that diatoms can be toxic or deleterious toŽ .copepods Ban et al., 1997 , our results do not indicate toxicity or nutritional insuffi-


ciency for the diatomN. closterium. By contrast, considering the possibility of certainmicroalgae to be toxic, or to produce compounds which reduce or inhibit embryonicdevelopment, the lower number of hatched nauplii in the mixed diet treatment may beexplained by a possible inhibitory effect ofT. gracilis.

The present values for survival and reproductive output ofTis. biminiensis weregenerally high compared with other published values forTisbe spp.; however, suchcomparisons must be made with caution, since differences may be explained by anumber of factors including the quantity and quality of the food source, previous culture

Ž .history and genetic differences between populations Williams and Jones, 1999 .Tis. biminiensis presented one of the highest values ofr obtained for a meiobenthic

copepod. The short generation time and high reproductive potential ofTis. biminiensismake the use of this copepod promising as live food in aquaculture. Although furtherstudies on the nutritional content of these copepods will be necessary in order to ensuretheir suitability as food for larval fish and crustaceans.

Acknowledgements

Ž .CSCP acknowledges a CAPES postgraduate research studentship Brazil . Theauthors acknowledge S.O. Lourenc¸o for microalgae strains, M. Costa and J. Abernathyfor English corrections.

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