Fermented mackerel processing by-products and soybean meal as alternative protein source in diets of juvenile black...

As compound bacteria fermented mackerel processing by-products mixed with soybean meal (FMPBS) has been reported to be a promising alternative to fish meal (FM) in aquafeeds, we hypothesized that replacing FM protein with FMPBS would support growth, feed utilization, and health performance of juvenile black rockfish (Sebastes schlegelii). Therefore, this study was conducted to evaluate the effects of replacing FM protein with FMPBS on growth, feed utilization, antioxidant activity, intestinal and liver morphology of black rockfish. Six isolipidic and isonitrogenous diets were formulated to replace FM protein by FMPBS at 0% (FMPBS0, control group), 20% (FMPBS20), 40% (FMPBS40), 60% (FMPBS60), 80% (FMPBS80) and 100% (FMPBS100), respectively. Fish (initial body weight, 10.36 ± 0.31 g) were randomly allotted to triplicate groups of 30 each and fed diets for 70 days. No significant differences were found in growth, feed intake and feed utilization of fish fed diets replacing up to 60% FM protein with FMPBS, while fish fed diets FMPBS80 and FMPBS100 had lower growth compared with the control group (P < 0.05). Fish fed diets FMPBS80 and FMPBS100 had significantly lower serum alkaline phosphatase activity than that fed diet FMPBS0, and fish fed diet FMPBS100 had lower total protein content than those fed diets FMPBS0 and FMPBS20 (P < 0.05). Fish fed diets FMPBS40 and FMPBS60 had significantly higher liver total superoxide dismutase activities than those fed diets FMPBS0 and FMPBS100 (P < 0.05). Fish fed diet FMPBS40 had higher catalase activity than those fed diets FMPBS80 and FMPBS100 (P < 0.05). The fish fed diet FMPBS100 had higher malondialdehyde content than those fed diets that replaced FM with FMPBS up to 60% (P < 0.05). Intestinal muscular layer thickness and villus length decreased with increasing FMPBS levels, and fish fed diets FMPBS80 and FMPBS100 had lower values (P < 0.05). Fish fed diets FMPBS80 and FMPBS100 resulted in hepatic steatosis and produced lesions. Overall, the findings suggest that FM protein could be replaced by 60% FMPBS without adverse effects on growth performance, feed efficiency and health of juvenile black rockfish, but replacing 80% and 100% FM protein with FMPBS had a negative impact on growth and health status.