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Effect of stocking density on water quality,
survival, and growth of larvae of the matrinxa,
˜
ž
/
Brycon cephalus Characidae , in ponds
L.C. Gomes
a, B. Baldisserotto
a,), J.A. Senhorini
ba
Departamento de Fisiologia, UniÕersidade Federal de Santa Maria, 97119-900 Santa Maria, RS, Brazil
b
Centro Nacional de Pesquisa em Peixes Tropicais, CP 64, 13630-970 Pirassununga, SP, Brazil
Accepted 6 August 1999
Abstract
Experiments were carried out in nine 64 m2 ponds at CEPTArIBAMA over a period of 21
Ž .
days in order to evaluate the effect of stocking density StD on survival and growth of larvae of matrinxa, Brycon cephalus. The larvae were randomly divided into treatments of 30, 60 and 120˜
2 Ž .
larvae m three replicates per treatment and fed three times a day. Samples of larvae were collected at days 0, 7, 14 and 21, and the length, weight, coefficient of variation of length, and specific growth rate were determined for each sample. Survival, production and food conversion were calculated at day 21. Data were analyzed statistically by ANOVA and Tukey’s multiple
Ž .
range test for mean separation P-0.05 . The following physicochemical parameters of the water were always at satisfactory levels for fish culture throughout the experiments: temperature, dissolved oxygen, pH, hardness, total alkalinity, ammonia and transparency. Increased StD significantly reduced length and weight from day 7, and increased the coefficient of variation of length on day 21. A correlation between specific growth rate and StD was observed only on day 14, and there was no correlation between StD survival. We conclude that an increase in StD reduces the growth and homogeneity but increases the production of B. cephalus larvae.q2000
Elsevier Science B.V. All rights reserved.
Keywords: Brycon cephalus; Larvae; Stocking density; Water quality; Survival; Growth
)Corresponding author. Tel.:q55-55-220-8342; fax:q55-55-220-8018; e-mail: bernardo@ccs.ufsm.br
0044-8486r00r$ - see front matterq2000 Elsevier Science B.V. All rights reserved. Ž .
1. Introduction
The matrinxa, Brycon cephalus, has been reared by researchers and producers in
˜
South America due to its good adaptation to captivity, fast growth, and omnivorous
Ž
feeding Werder and Saint-Paul, 1978; Reimer, 1982; Eckmann, 1984; Saint-Paul,
.
1986 . The amount of fingerlings produced has been the main problem for commercial development of this species, since the transformation from larvae to fingerling is the most difficult stage of production. Probably the main reason for the low yield of larviculture is the aggressive behavior of this and other species of the genus Brycon
ŽWoynarovich and Sato, 1989 . Consequently, the use of an appropriate stocking density. ŽStD in ponds could be a solution to this problem..
StD affects growth rate and probably is one of the most important reasons for failure
Ž .
to produce fingerlings Hepher and Prugnin, 1981 . According to Araujo-Lima and
´
Ž . Ž .
Goulding 1997 , survival of tambaqui larvae Colossoma macropomum in ponds is
Ž .
highly variable 0%–66% , and the reason for this mortality remains unexplained. The same authors stated that StD may be the major cause of this variable survival. Therefore, it is essential to evaluate the influence of StD on individual fish growth and the effects of this parameter on biomass gain by the group as a whole, since individual growth rate can be higher at low StD, but biomass production of the group can be higher at higher
Ž .
StD Jobling, 1994 .
The aim of this study was to determine the effect of StD on water quality, survival and growth of larvae of matrinxa, B. cephalus, and to contribute to the production
˜
technology for this species.
2. Materials and methods
2 Ž .
The experiments were conducted in nine 64 m ponds 8 m=8 m=1.2 m located
Ž .
at the Centro Nacional de Pesquisa em Peixes Tropicais CEPTArIBAMA , Brazil. All ponds had concrete walls, a clay floor, a concrete kettle drain system, and water coming from a dam through individual open masonry channels. Water was filtered through a nylon screen of ca. 300mm mesh to prevent the entry of predators. The ponds were left
Ž 2.
empty for 5 days before the experiments. Dolomitic lime 30 grm was then added and the ponds were filled up to 1.2 m depth. Water was renewed only to compensate for losses by evaporation and infiltration, and when oxygen levels were lower than 4 mg
y1 Ž y2. Ž y2.
l . Cattle feces were added to the ponds 1 500 g m and 9 175 g m days after
Ž y2.
the addition of lime. The ponds also received triple superphosphate 5 g m 2 days after the first organic manuring. The larvae were placed in the ponds 7 days after filling.
Ž .
Spawning to obtain the eggs was induced, as described by Bernardino et al. 1993 . All the eggs were from the same cohort and were incubated in Hungarian-model
Ž .
hatcheries 60 l with running water. Following the procedures of Woynarovich and Sato
Ž1989 , curimbata Prochilodus scrofa larvae were added to the hatcheries 34 h after.
´
Ž .bladder, and horizontal swimming, and therefore were considered to be ready for the experimental ponds.
The larvae were randomly divided into treatments of 30, 60 and 120 larvae my2
Žthree replicates per treatment . They were fed until satiety after day 5 it was possible to. Ž
. Ž
observe the larvae feeding on the water surface three times a day 0800, 1300 and 1700
. Ž . Ž .
h with fish meal 35.1% crude protein prepared at CEPTArIBAMA Table 1 . Granule size of the fish meal was 1 mm up to day 14, and 3 mm thereafter. Samples of larvae were collected on days 0, 7, 14 and 21, and length and weight of the larvae were measured. The size of samples collected was proportional to the StD: low StDs30, medium StDs60, and high StDs120 larvae, to avoid changes in StD during the
Ž .
experiments. The coefficient of variation of length CVl was calculated to analyze the homogeneity of the larvae in each treatment. CVl was obtained according to the following equation:
CVs
Ž
SDrX 100.
where SD is the standard deviation and X is the mean length.
Ž .
Specific growth rate G is commonly used to evaluate the effect of different
Ž
treatments on fish growth Troschel and Rosch, 1991; Elliot and Hurley, 1995; Johnson
.
and Dropkin, 1995 . G was calculated for each collection according to Jørgensen and
Ž .
Jobling 1993 . On day 21 the ponds were completely drained and all surviving
Ž .
fingerlings on this day fishes can be considered as fingerlings were collected to
Ž . Ž y2.
determine survival % and production fingerlings m . Food conversion was calcu-lated according to the following equation:
Food conversionsfood g
Ž .
rweight gain g .Ž .
Temperature was determined with a manual thermometer and dissolved oxygen with an oxygen meter, YSI model 57, once a day. There is a diurnal change in the dissolved oxygen concentration in fish culture ponds, and lower concentrations are always
Ž .
observed about 0600 h Boyd, 1982 . Water was always measured at 0800 h to determine the near-minimum concentrations of dissolved oxygen. The following physicochemical parameters of the water were analyzed at three day intervals: pH, using a pHmeter Fisher model 110; and total alkalinity, total hardness, total ammonia, and
Table 1
Composition of the feed used for B. cephalus larvae
Table 2
Physicochemical parameters of pond water during the larviculture of B. cephalus
Ž .
Mean values"S.E.M. Means identified by different letters on the rows were significantly different P-0.05 as determined by ANOVA and Tukey’s comparison of mean values.
y2
Temperature 8C 28.07"0.21 27.82"0.22 27.91"0.22
y1 a a a
Ž .
Dissolved oxygen mg l 5.26"0.39 5.57"0.33 5.08"0.31
a a a
Ž .
pH units 6.28"0.03 6.33"0.06 6.28"0.04
y1 a ab b
Ž .
Total hardness mg l CaCO3 23.25"1.09 20.37"1.06 19.38"0.82
y1 a b b
Ž .
Total alkalinity mg l CaCO3 24.04"1.05 21.46"0.44 21.57"0.44
y1 a a a
Ž .
Total ammonia mg l 0.18"0.02 0.15"0.02 0.18"0.02
a a a
Ž .
Transparency cm 95.88"2.49 97.25"3.35 98.00"3.64
Ž .
transparency according to Boyd 1982 . According to the same author, if these physico-chemical parameters of the water are at adequate levels, they do not influence food
Ž .
ingestion and growth in spite of diurnal changes , and it is not necessary to determine them every day.
All data are expressed as mean"S.E. Treatment groups were compared by one way ANOVA, and means were compared by Tukey’s multiple range test, with the level of
Table 3
Ž y2. Ž y2.
Growth of B. cephalus larvae at different StDs, i.e., low 30 larvae m , medium 60 larvae m and high
Ž120 larvae my2.
Coefficient of variation of length %
a a a
Number of replicates per treatment. Number in parenthesis indicates size of the sample in each pond. Means
Ža b ab c. Ž .
significance set at P-0.05. The statistical software program Sigma Stat, version 2.0, was used for data analysis.
3. Results
Throughout the experiment most physico-chemical parameters of the water were maintained within the appropriate range for larval production, at least at the time of
Ž . Ž .
sampling Boyd, 1982 , and for Characidae fishes in general Saint-Paul, 1986 . The
Ž y1
exception was dissolved oxygen levels on days 20 values of approximately 3.0 mg l
. Ž y1 y1
in all treatments and 21 low StDs2.0 mg l , medium StDs2.37 mg l , and high y1.
StDs1.53 mg l . Hardness and total alkalinity were significantly higher for the low
Ž y2. Ž y2.
StD 30 larvae m than the high StD 120 larvae m . Other physicochemical
Ž .
parameters did not show any significant differences among treatments Table 2 . There was a trend of decreased length of larvae with increasing StD, starting on day 14. Also starting on day 14 fish reared at low StD were significantly higher in weight than those reared at medium and high StD. Fish reared at low StD also showed lower CVl than fish reared at medium and high StD, but only on day 21. G was higher in fish
Ž . Ž . Ž . Ž .
reared at low StD than at high StD on day 14, but on day 21 there was no significant difference among the three treatments. The above data are presented in Table 3.
Ž
Survival and food conversion were not significantly different among treatments Fig.
.
1A and B . There was significantly higher production of fish at high StD than at low
Ž .
StD, but fish production at medium StD did not differ from high or low StD Fig. 1C .
4. Discussion
To evaluate the effect of StD on fish growth, physicochemical parameters must be
Ž .
within ideal ranges Jobling, 1994 . There were no significant differences in physico-chemical parameters among treatments, except hardness and total alkalinity. Although
Ž .
StD altered water quality in this experiment hardness and alkalinity , it had no such
Ž . Ž .
influence in channel catfish Ictalurus punctatus Esquivel et al., 1997 . According to
Ž .
ranges specified by Boyd 1982 , all values determined in this study were adequate levels for fish culture, with the exception of dissolved oxygen levels on days 20 and 21. Nevertheless, it is possible that early morning dissolved oxygen levels in this experiment
Ž .
were within the range that can retard growth in teleosts Boyd, 1982 . Guttierrez and
´
Ž .
Guevara 1988 found that B. cephalus can survive in waters with lower dissolved oxygen levels than observed in the present study, but levels in which growth in this species is reduced are not determined yet. Additional experiments using higher dissolved oxygen levels or higher number of replicates must be done to determine if the observed dissolved oxygen levels could affect growth of B. cephalus larvae.
The increase in StD reduced the length and weight of B. cephalus larvae after day 14. High StD reduces the space available to each larva and therefore also reduces their
Ž .
growth Hepher and Prugnin, 1981 . Increased StD also reduced the length and weight
Ž
of larvae of related species, such as ‘‘paqui’’ female of Piaractus mesopotamicus=
. Ž . Ž
male of C. macropomum Fontes et al., 1990 and P. mesopotamicus Fontes and
.
Senhorini, 1994 .
The heterogeneous growth of larvae and fingerlings is usually related to feeding competition and stress due to social interactions, with subordinate fishes being most
Ž .
affected by these factors Koebele, 1985 . This social hierarchy increases with increase
Ž .
in StD Huntingford et al., 1990 . Probably these factors are also important for the larvae of B. cephalus since CVl increased with increased StD on day 21.
G values were similar for all treatments on day 7, and larvae doubled their size each 2.5 days, showing the good growth potential of this species. Comparable values of G
Ž . y2
were found by Bernardino et al. 1993 using an StD of 30 larvae m . The significantly higher G value at the low StD during the second week showed that space began to limit growth at the high StD. A change in water quality could reduce growth, but the physicochemical parameters were not significantly different among treatments. Since larvae received food until satiety, the amount of food available to the larvae also cannot explain the difference in G among treatments on day 14.
Ž .
Previous experiments with the same species showed only 8% survival, and the authors stated that lack of adequate food during hatching was the most probable reason for this
Ž .
low survival Bernardino et al., 1993 . The survival obtained for B. cephalus larvae at all tested StDs was generally higher than obtained in other experiments with similar
Ž .
StDs Table 4 , indicating that intensive culture of this species at high StD is feasible. StD did not alter survival of B. cephalus larvae. The same was also observed for
Ž . Ž .
survival of channel catfish I. punctatus fingerlings Esquivel et al., 1997 . However, these results cannot be considered a general rule. Certainly higher StDs than those employed in our experiments would affect survival.
The food conversion values were low and comparable to those obtained for other
Ž
larvae and fingerlings D’Silva and Maughan, 1995; Cole et al., 1997; Esquivel et al.,
.
1997 . StD did not change food conversion of matrinxa larvae, in disagreement with
˜
Ž
experiments with red tilapia Oreochromis mossambicus=Oreochromis urolepis
horno-. Ž . Ž . Ž
rum D’Silva and Maughan, 1995 and bighead carp Aristichthys nobilis Engle,
.
1982 , in which lower StD increased food conversion. Channel catfish fingerlings
Ž
increased their food conversion when fed more than once a day Jarboe and Grant,
.
1997 . In our experiment food was offered three times a day and, since matrinxa larvae
˜
are very voracious, it was possible to observe feeding larvae and to reduce the amount of fishmeal residues, which are common in larval culture. This feeding procedure probably was the main reason for the lack of effect of StD on food conversion by matrinxa larvae.
˜
Production is a parameter not commonly assessed in pond culture of larvae of tropical fishes. However, it provides an excellent economic evaluation of different treatments, since in Brazil fingerlings are sold by the unit. The choice of the StD to be used in larval culture depends on the aim of the producer: fingerling sale or growing. Since there was no significant difference among the StDs studied here in terms of survival, food conversion or water quality, the highest production at 120 larvae my2 demonstrated that
this is the best StD if the aim is to produce fingerlings for sale. Moreover, even at this
Ž . Ž
StD where length was reduced fingerling size was sufficient for sale. Low StD e.g., y2.
30 larvae m is recommended if the aim of the producer is to rear the fingerlings of uniform size, since length is higher and size heterogeneity is lower compared to higher StDs.
Table 4
Survival obtained in experiments with various fish larvae y2
Ž . Ž .
Species StD larvae m Days of rearing Survival % Reference
Ž .
Polyodon spathula 6.18 – 79 Mims et al. 1995
Ž .
StizostedionÕitreum 20 45 60.9 Soderberg et al. 1997
B. cephalus 30 21 71.9 This study
Ž .
B. cephalus 30 37 8 Bernardino et al. 1993
Ž .
P. mesopotamicus 40 30 44 Fontes and Senhorini 1994
B. cephalus 60 21 60.9 This study
Ž .
P. mesopotamicus 80 30 23 Fontes and Senhorini 1994
B. cephalus 120 21 49.7 This study
Ž .
Acknowledgements
The authors wish to thank the directors of CEPTA-IBAMA for providing technical facilities, and CAPES and the Animal Husbandry post-graduate course for financial support. We also would like to thank MSc Adriana R. Chippari Gomes for a critical reading of this article.
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