The use efficiency and feed conversion of extruded and pelletized diets were compared. Eight isoproteic diets (220 g kg )1 digestible protein) were assayed for 90 days in a 2 · 2 · 2 multifactorial design with two carbohydrate levels (400 and 500 g kg )1 ), two lipids levels (40 and 80 g kg )1 ) and two diet processing (pelletization and extrusion) with three repetitions. The growth of Piaractus mesopotamicus fed with these diets and the quality control indices of diets were gauged. The density of extruded diets was lower as carbohydrate level was 400 g kg )1 and lipid 40 g kg )1 . The interaction carbohydrate and diet processing presented higher leaching value for low carbohydrate level in extruded diet. Fish fed with extruded diets presented the best feed conversion and protein efficiency ratio. When high levels of carbohydrate and lipid are combined, the weight gain is impaired. The interaction between diet processing diet and lipid levels resulted in the best fish performance when pelletized diets with 40 g kg )1 lipid or extruded diets with 80 g kg )1 lipid were considered. The protein efficiency ratio increased with the increment of carbohydrates in the pelletized diets. The fish show low tolerance to lipids and a preference for carbohydrate when the lipid productive values are taken into account. KEY WORDS

The responses of the digestive physiology of juvenile pacu to different diet processing were studied. Fish were fed with isoproteic diets with 260 g kg À1 of crude protein (CP) containing different levels of carbohydrate (DCh) (400 or 500 g kg À1 ), and two diet processing (pelletization or extrusion) for 90 days. Fish fed with extruded diets showed decrease of the gastrointestinal transit time (GI transfer) and of the amylase activity, but maltase activity did not alter. Protease activity of intestine depicted increase when the DCh was raised. The increase of DCh also caused enhancement of the apparent digestibility coefficient of CP (ADC CP ) in fish fed with extruded diets. Fish fed with pelletized diets showed increase of the amylase activity in pyloric caecum independently of the dietary carbohydrate level. No interaction was observed between dietary carbohydrate level and diet processing. Maltase activities from the stomach and intestine of pacu were not responsive to the carbohydrate level. The extrusion process improved the carbohydrate availability and the digestion efficiency of protein in pacu. Digestive enzymes of pacu were modulated either by nutrients or diet processing.

-The objective of this work was to evaluate the effect of sustained swimming and dietary protein levels on growth and hematological responses of juvenile pacu (Piaractus mesopotamicus). A completely randomized design was used in a 3x2 factorial arrangement, with three levels of dietary protein (24, 28, and 32% crude protein), two rearing conditions (sustained swimming or motionless water), and 15 replicates. Fish were subjected to sustained swimming at the velocity of two body lengths per second (2 BL s -1 ), for 45 days. The level of dietary protein and the swimming conditions affected the performance, growth, and hematological profile of pacu. Swimming conditions influenced nutritional factors, increasing daily weight gain, specific growth rate, number of erythrocytes, mean corpuscular volume, and mean corpuscular hemoglobin. Fish under sustained swimming and fed with 24% crude protein showed better growth performance, with higher specific growth rate (4.11±0.88) and higher daily weight gain (2.19±0.47 g per day). Sustained swimming can increase the productive performance of pacu and simultaneously reduce dietary protein levels.Index terms: Piaractus mesopotamicus, erythropoiesis, exercise, growth rate, weight gain. Crescimento e hematologia de pacu submetido a natação sustentada e alimentado com diferentes níveis proteicosResumo -O objetivo deste trabalho foi avaliar o efeito da natação sustentada e de níveis de proteína na dieta sobre o crescimento e a resposta hematológica de juvenis de pacu (Piaractus mesopotamicus). Utilizou-se o delineamento inteiramente casualizado, em arranjo fatorial 3x2, com três níveis de proteína na dieta (24, 28 e 32% de proteína bruta), duas condições de criação (natação sustentada ou água imóvel) e 15 repetições. Os peixes foram submetidos à natação sustentada na velocidade de duas vezes o comprimento corporal por segundo (2 CC s -1 ), por 45 dias. O nível de proteína da dieta e as condições de nado afetaram o desempenho, o crescimento e o perfil hematológico do pacu. As condições de nado influenciaram os fatores nutricionais, com aumento de ganho de peso diário, taxa de crescimento específico, número de eritrócitos, volume corpuscular médio e hemoglobina corpuscular média. Peixes sob natação sustentada e alimentados com 24% de proteína bruta apresentaram melhor desempenho de crescimento, com maior taxa de crescimento específico (4,11±0,88) e maior ganho em peso diário (2,19±0,47 g por dia). A natação sustentada pode aumentar o desempenho produtivo de pacus e ao mesmo tempo reduzir os níveis de proteína na dieta.Termos para indexação: Piaractus mesopotamicus, eritropoiese, exercício, taxa de crescimento, ganho em peso.

-The objective of this work was to evaluate the effect of stocking density associated with the swimming exercise on the stress responses of Brycon amazonicus. During 70 days, fish were subjected to three stocking densities: LD, low density of 88 fish per cubic meter; ID, intermediary density of 176 fish per cubic meter; and HD, high density of 353 fish per cubic meter. These densities were combined with static water (non-exercised group) or moderate-speed water (exercised group). Chronic stress was observed in HD, and plasma cortisol and glucose increased with the stocking densities. In HD, levels of plasma cortisol were significantly lower in exercised fish (135 ng mL ). The greatest hepatic glycogen bulks occurred in fish kept in ID and sustained swimming. Hepatic free amino acids (FAA) increased with the stocking density, particularly in non-exercised fish. The contents of FAA in the liver and of free fatty acids (FFA) in the liver and muscle were mobilized to meet the metabolic demands imposed by exercise and stocking density. The hematological parameters remained stable. The results show that Brycon amazonicus is more resistant to stress when subjected to sustained swimming and high stocking density than to static water. ). Os maiores acúmulos de glicogênio hepático ocorreram em peixes mantidos em DI e em natação sustentada. Os aminoácidos livres (AAL) hepáticos aumentaram com a densidade de estocagem, particularmente nos peixes não exercitados. As reservas de AAL hepáticos e de ácidos graxos livres hepáticos e musculares foram mobilizados para atender às demandas metabólicas impostas pelo exercício e pela densidade de estocagem. Os parâmetros hematológicos mantiveram-se estáveis. Os resultados são indicativos de que o matrinxã é mais resistente ao estresse quando submetido à natação sustentada e à alta densidade de estocagem que à água parada.Termos para indexação: bem-estar animal, piscicultura intensiva, respostas metabólicas, exercício físico.

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