Effect dietary energy levels and feeding rates on growth and body composition of fingerling rainbow trout (Oncorhynchus mykiss)

Growth, feed conversion ratio and fillet composition of rainbow trout (initial weight of 9.99 +/- 0.109) were investigated in a 6x2 factorial design experiment employing two levels of digestible energy (DE) (2900 and 3500kcal.kg(-1)) and six feeding rates (1.0%, 2.0%, 3.0%, 4.0%, 5.0% of the body weight (BW) day(-1) and to satiation) for 60 days. Specific growth rate (SGR) was highest at 5.0% ration in both levels of digestible energy and decreased in the satiation ration. Regardless of feeding rate, rainbow trout grew more by 35% in DE 3500 kcal kg(-1). There was a significant (P < 0.05) interactive effect of feeding rates and DE on weight gain and feed conversion ratio (FCR). The highest FCR was found in fish fed to satiation (19-21%), while the lowest FCRs, were found in 4%, 3% rations in DE levels of 2900 and 3500kcal kg(-1), respectively. There was a significant increase in protein and fat levels and decrease in moisture content of fish fillet (P < 0.05) as feeding rate and DE increased (P < 0.05). Condition factor increased when feeding rate and DE increased (14-15%). Feeding rate and DE level proved to be the main differentiating factors in growth, FCR and fillet composition parameters. Values of SGR and FCR plotted against feeding rates allowed the optimum and maximum feeding levels to be determined, which were found to be at 4% and 3%kcal day(-1) in DE levels of 2900 and 3500kcal kg(-1), respectively, for the rainbow trout of 10g average weight.