Effects of dietary inclusion of fermented soybean meal on growth, body composition, antioxidant enzyme activity and disease resistance of rockfish (Sebastes schlegeli)

Abstract

Two experiments were conducted to investigate the effects of replacing fish meal (FM) with fermented soybean meal (FSM) on growth performance, body composition, antioxidant enzyme activity and disease resistance of rockfish, Sebastes schlegeli, at the juvenile and grower stages. Five isonitrogenous (51%) and isocaloric (21.0MJkg−1) diets were formulated to contain 0, 8, 16, 24 and 32% FSM, replacing approximately 0, 10, 20, 30 and 40% of the FM protein (designated as FSM0, FSM8, FSM16, FSM24 and FSM32, respectively). Each experimental diet was fed to triplicate groups of juvenile (1.2±0.04g; EXP I) and grower (148.2±2.9g; EXP II) rockfish to apparent satiation twice daily for 8weeks. Juvenile rockfish fed the FSM32 diet showed significantly lower weight gain (WG) than those fed the FSM0, FSM8 and FSM16 diets. Feed efficiency (FE) and protein efficiency ratio (PER) of fish fed the FSM16, FSM24 and FSM32 diets were significantly lower than those of fish fed the FSM0 and FSM8 diets. Fish fed the FSM24 diet exhibited significantly lower daily feed intake (DFI) than fish fed the FSM0 and FSM8 diets. However, growth performance and feed utilization efficiency of grower rockfish did not show any definite pattern of change due to feed composition. The viscerosomatic index (VSI) of juvenile fish fed the FSM32 diet was significantly lower than those of all the other experimental groups. Replacement of FM with FSM, up to 40%, had no significant effect on whole body and muscle proximate and amino acid compositions of juvenile and grower rockfish, respectively. The plasma antioxidant enzyme activity of grower fish was significantly enhanced by the dietary inclusion of the FSM compared with the control group. Survival of juvenile fish after intraperitoneal injection of Edwardsiella tarda was not affected by dietary treatment. These results indicate that FSM can be used successfully as a replacement for FM at levels up to 10% in diets for juvenile rockfish while at least 40% of dietary FM protein can be replaced by FSM without causing any adverse effect on grower rockfish performance. Statement of relevance1.There have been a few studies examining the efficiency of fermented soybean meal (FSM) as a possible fish meal substitute in fish feed. However, to the best of our knowledge no studies have been reported on the use of FSM as a substitute for fish meal in diet for rockfish.2.The results of this study indicate that FSM can be used successfully as a replacement for FM at levels up to 20% in diets for juvenile rockfish while at least 40% of dietary FM protein can be replaced by FSM without causing any adverse effect on grower rockfish performance.3.As feed cost accounts for almost half of the fish production costs, the results of our experiments can be useful for formulation of more cost-effective practical diets for juvenile and grower rockfish.