With the purpose of evaluating the changes and the degree of heterosis on performance and carcass traits of fish from the diallel crossing between Pacu and Tambaqui, four genetic groups were generated through hormonal induction: pacu, tambaqui, tambacu and paqui. For 196 days, 400 juveniles of each genetic group were stocked in a pond divided into four parts of equal size, one for each group. At the end of this period, when the fish weighed on average 1024 g (±115.52 g), 20 specimens of each genetic group were sampled, weighed, measured: head length; standard length; body height; and width; and also processed resulting in following body yield: viscera; carcass; head; fillet; rib; residue and skin yields. There was positive heterosis for body weight, viscera and skin yield and head measures and negative heterosis for carcass and filet yield and body width, indicating that the hybrids have better performance on weight gain, but are inferior in relation to the carcass conformation.

The objective of this study was to verify which morphometric measures and ratios are more directly associated with the weight and body yields of rounded fish. A total of 225 specimens of rounded fish (59 pacus, 61 tambaquis, 52 tambacus and 53 paquis) with average weight of 972.43 g (±115.52 g) were sampled, stunned, slaughtered, weighed, measured, and processed for morphometric and processing yield analysis. The morphometric measures taken were: standard length (CP); head length (CC); head height (AC); body height (A1); and body width (L1). For completeness, the following morphometric ratios were calculated: CC/CP, AC/CP, A1/CP, L1/CP, CC/A1, AC/A1, L1/A1, CC/AC and L1/CC. The yields of carcass, filet, rib and filet with rib were estimated after processing. Initially, a "stepwise" procedure was performed in order to eliminate multicollinearity problems among the morphometric variables, and the phenotypic correlations were then calculated for the dependent variables (weight and body yields) and independent variables (morphometric measurements and ratios). These correlations were later deployed in direct and indirect effects through path analysis, and the direct and indirect contributions of each variable were measured in percentage terms. The CC and A1 measures were important for determining the weight of rounded fish. The CC/A1 ratio was the variable most directly associated with carcass yield. For filet, filet with rib and rib yields, the L1/CC ratio was found to be more appropriate and can be used directly.

Com o objetivo de determinar os níveis de energia digestível (ED) em função do nível de proteína bruta (PB) da ração para alevinos de lambari tambiú (Astyanax bimaculatus), foram utilizados 600 peixes com 1,30 ± 0,01 g, distribuídos em 40 aquários de 100 L, dotados de abastecimento de água, com temperatura controlada e sistema de aeração individual. O experimento foi realizado em um esquema fatorial 5 x 2 (cinco níveis de ED: 2.900, 3.000, 3.100, 3.200 e 3.300 kcal/kg combinados com dois níveis de PB: 32,0 e 38,0%), em delineamento inteiramente ao acaso, com quatro repetições e 15 peixes por unidade experimental. Os peixes foram submetidos à alimentação controlada com base no consumo diário médio dos peixes dos tratamentos com rações contendo nível mais alto de energia (3.300 kcal/kg) para cada nível protéico, corrigido diariamente, durante 49 dias. Foi avaliado o ganho de peso, a taxa de crescimento específico, os consumos de ração, de PB e de ED, a conversão alimentar, a taxa de eficiência protéica, o rendimento de carcaça, a eficiência de retenção de nitrogênio e os teores de umidade, proteína e gordura corporais. Com o nível de 32% de PB, foram obtidos maiores consumos de ração e de ED, mais altas taxas de eficiência protéica e de retenção de nitrogênio, menores consumo de PB e rendimento de carcaça, além de reduzida umidade corporal. Com níveis crescentes de ED nas rações com 32% de PB, os peixes apresentaram menor taxa de crescimento específico, mais baixa taxa de eficiência protéica e maior conversão alimentar, enquanto com as rações com 38% de PB apresentaram maior rendimento de carcaça. A exigência de ED para lambari tambiú é de 2.900 kcal/kg para rações com 32 e 38% de PB.

Six hundred lambari tambiú (Astyanax bimaculatus) averaging initial weight of 1.30 ± 0.01 g, placed in 40 aquariums (100 L) with water renewal, controlled temperature and individual aeration, were used to determine the digestible energy (DE) requirements, according to the dietary crude protein (CP) levels. The experiment was analyzed as a 5 x 2 factorial scheme (five levels of DE: 2,900, 3,000, 3,100, 3,200, and 3,300 kcal/kg, combined with two levels of CP: 32 and 38%), in a completely randomized design with four replicates and fifteen fishes per experimental unit. The fish were submitted to the feeding controlled based on the average daily intake of the treatments with the highest energy level (3,300 kcal/kg) for each daily corrected protein level, during 49 days. Weight gain, specific growth rate, feed intake, crude protein intake, digestible energy intake, apparent feed:gain ratio, protein efficiency rate, carcass yield, nitrogen retention efficiency, and contents of body humidity, fat and protein were evaluated. Fishes fed diets with 32% of CP showed smaller specific growth rate and protein efficiency rate and higher feed:gain ratio. Fishes fed diets with 38% of CP showed greater carcass yield. The requirement of digestible energy for lambari tambiú is of 2,900 kcal/kg for diets with 32 and 38% of CP.

Objetivando-se determinar as exigências de proteína bruta (PB) em função do nível de energia digestível (ED) da dieta para alevinos de curimbatá (Prochilodus affins), foram utilizados 256 peixes com peso inicial de 2,72 ± 0,11 g, mantidos em 32 aquários de 100 L, dotados de abastecimento de água, temperatura controlada e aeração individuais. O experimento foi realizado seguindo-se esquema fatorial 4 x 2 (quatro níveis de PB: 18,0; 22,0; 26,0; e 30,0%, combinados com dois níveis de ED: 2.700 e 3.000 kcal/kg), em um delineamento inteiramente ao acaso, com quatro repetições e oito peixes por unidade experimental. Os peixes foram alimentados ad libitum em duas refeições diárias durante 78 dias. Avaliaram-se o ganho de peso, o consumo aparente de racão, a conversão alimentar aparente, a taxa de crescimento específico, a taxa de eficiência protéica, a eficiência de retenção de nitrogênio, a umidade, a proteína e a gordura corporais e as porcentagens de nitrogênio e de gordura no ganho de peso. Verificou-se que não houve interação dos níveis de PB <FONT FACE=Symbol>´</FONT> ED, à exceção da porcentagem de gordura no ganho de peso. Com o nível de 3.000 kcal de ED/kg, obtiveram-se peixes com maiores níveis de matéria seca, gordura corporal e porcentagem de gordura no ganho de peso. Concluiu-se que a exigência de PB e ED para alevinos de curimbatá é de 26,05% e 2.700 kcal/kg, respectivamente, que corresponde a uma relação ED:PB de 10,36 kcal de ED/g de PB, por proporcionar as melhores respostas em ganho de peso e composição de carcaça.

Two hundred and fifty six curimbatá (Prochilodus affins) fingerlings averaging initial weight of 2.72 ± 0.11 g, stocked in 32 aquariums (100 L) with water renewal, controlled temperature and individual aeration, were used to determine the dietary crude protein (CP) requirements, according to the digestible energy level (DE). The experiment was carried out in to a 4 x 2 factorial scheme (four CP levels: 18.0, 22.0, 26.0 and 30.0% combined with two DE levels: 2,700 and 3,000 kcal/kg), according to a completely randomized design with four replicates of eight fishes. The fishes were fed ad libitum twice a day, during 78 days. Weight gain, apparent feed intake, apparent feed:gain ratio, specific growth rate, protein efficiency rate, nitrogen retention efficiency, humidity, body fat and protein, nitrogen and fat percentage in weight gain were evaluated. No CP <FONT FACE=Symbol>´</FONT> DE levels interaction was observed for any studied variable, except for the fat percentage in weight gain. Fishes fed diets with 3,000 kcal de DE/kg showed higher levels of dry matter, body fat and fat percentage in weight gain. It was concluded that CP and DE requirements for curimbatá fingerlings are of 26.05% and 2,700 kcal/kg, respectively, that correspond to DE:CP ratio of 10.36 kcal DE/g CP, due to the best results of weight gain and carcass composition.