Dietas práticas com diferentes níveis de proteína e energia na alimentação de juvenis de pirarucu Arapaima gigas (SCHINZ, 1822) durante a engorda em tanque-rede

Abstract

The arapaima, Arapaima gigas, is considered one of the most promising species to the aquaculture, due to its fast growth, performance and excellent flesh quality and dress out yield. As a carnivore, it depends on diets with high levels of protein and, in order to have the use of this nutrient optimized, its dietary optimal levels need to be determined. This study evaluated the effect of increasing protein and energy levels in practical diets on the performance, physiological responses, body yield and fillet composition of juvenile arapaima during the grow out stage in net cage intensive system. Following a randomized design, 225 arapaima juveniles with initial weight of 2025±335 g were distributed in 15 net cages with 5.3 m3 each installed in a white water lake of Central Amazonia. Fishes were fed to apparent satiation during 88 days with extruded diets containing 37.4, 40.8, 43.9, 45.5 and 47.1% of crude protein (CP) and energy/protein ratio fixed at 10 kcal.g-1. Water quality parameters and feed intake of each experimental unit were measured daily. At the end of the experiment, fish biometric measurements were taken for performance parameters determination. Hemoglobin concentration [Hb]; hematocrit (Ht); number of erythrocytes (RBC) and red cells indices were measured. In the plasma, concentrations of glucose, cholesterol, triglycerides, total protein, albumin and cortisol were determined. The 37.4% CP diet resulted in the best protein efficiency ratio (PER) (p<0.01), highest concentration of protein in the fillet (p<0.01), lowest lipid in the fillet (p=0.02) and lowest blood cholesterol (p<0.01), as well as the lowest cost compared in relation to weight gain (p<0.01). There was observed increased viscerossomatic index (p=0.02) and visceral fat (p <0.01) of fishes fed with 43.9% CP diet, due to the increase of lipid metabolism in the fish in consequence of excess energy in the most protein diets. The results indicate that dietary protein level less, between the diets tested (37.4% CP), provided better protein utilization and lower fat concentration in the tissues and bloodstream of the fish, and have lower cost of feed per kg of the produced pirarucu in the grow out stage in net cages.