Influence of feeding diets with and without fish meal by hand and by self-feeders on feed intake, growth and nutrient utilization of juvenile rainbow trout (Oncorhynchus mykiss)

Feed intake, growth performance and nutrient utilization by juvenile rainbow trout fed diets with and without fish meal were compared between two feeding regimes: manual feeding and self-feeding. A fish meal-based diet and two non-fish meal diets, fortified with and without essential amino acids (EAA) to simulate the EAA composition of the fish meal diet, were prepared. The two non-fish meal diets were composed mainly of extruded defatted soybean meal (ExSBM), meat and bone meal (MBM) and corn gluten meal (CGM). Each diet was fed to four replicate groups (initial BW; 19.0 +/- 2.3 g, 700 g/60 l tank) either by hand to apparent satiation twice daily (0800 and 1730 h) or by self-feeders (feeds were dispensed by fish demands during the light phase) for 60 days at 17 degrees C under a 14 h light and 10 h dark cycle. Feeding regime did not significantly affect feed intake, weight gain, protein and energy retention, or whole body proximate composition (P>0.05). Fish fed with the non-fish meal diet with EAA supplementation attained equivalent weight gain and retention of protein as the fish fed with the fish meal diet. However, these parameters for fish fed with the non-fish meal diet without EAA supplementation were significantly inferior (P<0.05). The whole body fat content of fish fed with this diet was significantly higher than that of fish fed with the other diets. Free EAA levels in the plasma of fish fed with the EAA supplemented non-fish meal diet were similar to those fed with the fish meal diet except for threonine, which was lower in the EAA supplemented non-fish meal diet group. The branched-chain amino acid levels in the plasma of the two non-fish meal diet groups fed by hand increased more sharply and reached higher levels after feeding compared with fish fed with the same diets by self-feeders. The low levels of free threonine, methionine and lysine in the dorsal white muscle of fish fed with the EAA-unsupplemented non-fish meal diet increased in fish fed with the EAA supplemented non-fish meal diet, this increase was especially notable in the manually fed fish. Free non-essential amino acid levels in muscle of fish fed with the non-fish meal diet without EAA were generally the highest among the treatments. The feeding regime affected the levels of serine, glycine and hydroxyproline levels in the muscle (manual feeding < self-feeding). The results of this study indicate that a combination of ExSBM, MBM and CGM, when EAA are supplemented, has the potential to totally replace fish meal in juvenile rainbow trout diets. Feeding diets by self-feeders proved to attain growth and feed performance comparable to those fed by hand. Self-feeding non-fish meal diets affected certain amino acid levels in the plasma and muscle but the effects were not reflected in their growth and protein utilization in this 60-day feeding period.