ABSTRACT This study aimed to evaluate the effect of different proportions of soybean and linseed oil to replace fish oil in diets for female lambari (Astyanax altiparanae). A completely randomized design with seven treatments and five replicates was used. The treatments consisted of a diet containing fish oil and six diets containing different proportions of soybean oil (S) and linseed oil (L), 10S/0L, 8S/2L, 6S/4L, 4S/6L, 2S/8L and 0S/10L. The fish that received the highest proportion of linseed oil (0S/10L) had the lowest crude lipid in their carcasses. The highest linolenic acid (18:3n3) concentrations were detected in the carcasses of fish fed diets with high proportions of linseed oil (4S/6L, 2S/8L, and 0S/10L). The highest n6/n3 ratios corresponded to the carcasses of fish fed diets containing the lowest proportions of linseed oil (10S/0L and 8S/2L). The highest levels of 20:5n3 (eicosapentaenoic acid [EPA]), 22:6n3 (docosahexaenoic acid [DHA]) and ZEPA+DHA occurred in fish fed diets containing fish oil. Among the fish that received diets with vegetable oils, the ZEPA+DHA was higher in the fish of the treatments 4S/6L, 2S/8L and 0S/10L. Diets supplemented with a 4S/6L proportion provide adequate deposition of the n3 fatty acids series in the lambari carcass.

This study ascertains the length-weight relationship and predicts body composition equations in cultivated Astyanax aff. fasciatus. A total of 300 fish were distributed in five groups according to body weight: 1.19 ± 0.18, 3.7 ± 0.70, 7.55 ± 0.97, 12.28 ± 2.32 and 22.16 ± 2.64 g. The length-weight relationship was elaborated using linear (y i = b0 + b1x i) or second-order (y i = b0 + b1x i + b1x i²) regression analysis. The value of the b slope in the length-weight relationship was 3.6971 and the intercept was 0.0031. The prediction equations obtained for body moisture, crude protein, crude lipid and ash were, y = 71.680 - 0.404BW, y = 17.140 - 0.095BW, y = 8.432 +0.364BW and y = 3.720 - 0.032BW, respectively, where BW is the body weight of fish (g). The use of prediction equations to describe body composition as a tool to support fish production and commercialization is suggested.

This work was undertaken out to the evaluate the replacement rates of carbon stable isotope (<FONT FACE=Symbol>13</FONT>C) in the muscle tissue of Pseudoplatystoma corruscans, during the juvenile stage is provided, based on the hypothesis that the consumer reveals its diet isotopically. Four hundred and eighty pintados, average life weight 0.71 ± 0.13 g and 45 days old, were distributed in 24 - 14 l aquariums. Previous to the experimental period and since the start of exogenous feeding, the fish were fed on nauplii artemia. After they were fed on post-larval guppies (Poecilia reticulata) for 13 days. Two fish from each aquarium were collected for d 13C analysis. Exponential model for muscle tissue of the pintado estimated a half-life equal 4.38 days. Exchanging time for 99% of carbon diet amounted to 29.91 days. Since results show that consumer reveals isotopic composition by its diet, the use of carbon stable isotope is validated in so far as time of substitution is concerned.

Este estudo foi realizado com o objetivo de avaliar a taxa de substituição do isótopo estável de carbono (13C) no tecido muscular do pintado, Pseudoplatystoma corruscans, na fase juvenil, baseado na hipótese de que o consumidor reflete isotopicamente sua dieta. Foram utilizados 480 juvenis de pintados, com peso vivo médio de 0.71 ± 0.13 g e 45 dias de vida após eclosão, distribuídos em 24 aquários de 14 l. Antes de iniciar o período experiemental e desde o início da alimentação exógena, os peixes foram alimentados com náuplios de artemia. Após este período foram alimentados com pós-larvas de lebistes (Poecilia reticulata) por 13 dias. Foram coletados dois peixes de cada aquário para análise de delta13C. Pelo modelo exponencial, obteve-se uma meia-vida para o tecido muscular do pintado de 4.38 dias. O tempo de substituição de 99% do carbono da dieta foi de 29.91 dias. Os resultados demonstraram que o consumidor reflete a composição isotópicas de sua dieta, validando o uso do isótopo estável de carbono como marcador de carbono.