Quality evaluation of different types of non-fish meal diets for yellowtail [Seriola quinqueradiata]

Two feeding experiments were conducted to evaluate the feed quality of non-fish meal diets having the same protein ingredient composition but prepared as different types and to deter mine the supplemental effect of crystalline essential arnino acids (EAA) on feed utilization by young yellowtail, Senola quinqueradiata. Non-fish meal diets formulated with soy protein concentrate defatted soybean meal, com gluten meal, meat meal, and krill meal were prepared as either soft dry pellets (SDP) or extruded pellets (EP) by using a large- or a small-sized twin screw extruder under different preparation conditions; or as a single moist pellet (SMP), each with and without EAA mixtures. Commercial yellowtail SDP was used as the control diet. Fish weighing 134g and 237g on average were reared with the experimental diets, for 93 (net cages) and 44 (aquariums) days, respectively. The fish fed both the control and test diets were found to have a good appetite. Growth rate and feed gain ratio were highest in the control diet roup. The physiological condition of fish fed the control diet was evaluated as superior compared to those on the non-fish meal diets. Among the non-fish meal diet groups, the best performances were obtained for fish fed the SDP type diet with EAA sup plement, and performance parameters excelled in the order of SDP, EP and SMP both among the diets with and without supplemental EAA. This suggests that the nutritional quality of non-fish meal diet was affected by the diet preparation method. It also indicates that supplementation of EAA could improve the guality of non-fish meal diets, irrespective of the diet type, probably as a result from the enhancement of feed protein utilization.