Effects of diet supplementation with plant juice processing by-products on juvenile black rockfish (Sebastes schlegelii) growth performance, feed utilization, non-specific immunity, and disease resistance against Vibrio harveyi

•Supplementation of by-product from yacon, ginger and garlic juice processing increased growth performance of rockfish.•Diets with yacon, ginger and garlic juice production by-products improved non-specific immunity, and antioxidant ability.•Dietary plant juice processing by-products enhanced disease resistance against Vibrio harveyi.•By-product from yacon, ginger and garlic juice processing can be considered functional feed additives in fish aquaculture. A seven-week feeding trial was conducted to evaluate the effects of vegetable and fruit juice processing by-product feed additives on juvenile black rockfish (Sebastes schlegelii) growth, feed utilization, non-specific immune responses, and resistance to Vibrio harveyi. Juvenile rockfish (n = 1050) were randomly distributed into 300 L circular tanks (50 fish per tank). Seven experimental diets were prepared in triplicate. The experimental diets were supplemented with 1% garlic, ginger, blueberry, tomato, onion, or yacon juice processing by-product powders, referred to as GLJB, GGJB, BBJB, TTJB, ONJB, and YCJB diets, respectively. No additives were included in the control (Con) diet. Three groups of fish were randomly assigned to each diet and fed to apparent satiation twice daily. After the feeding trial, fish were challenged by V. harveyi infection, and cumulative survival was observed for 10 d. Weight gain, specific growth rate, feed consumption, feed efficiency, and protein efficiency ratio were significantly higher in fish fed the YCJB, GLJB, and GGJB diets than in fish fed the Con diet. Lysozyme activity was significantly higher in fish fed the GLJB, YCJB, and BBJB diets than those fed the Con diet. Superoxide dismutase and catalase activities and glutathione concentration were significantly higher in fish fed the YCJB, GGJB, and GLJB diets than fish fed the Con diet. No differences in the whole-body composition and plasma hematological parameters were observed among fish fed different diets. All the diets supplemented with plant juice processing by-products improved fish survival rate after the V. harveyi challenge compared to that of fish fed the Con diet. In conclusion, dietary inclusion of YCJB, GGJB, and GLJB contributed to improving growth performance, feed utilization, non-specific immune response, and resistance against V. harveyi in rockfish. Thus, yacon, ginger, and garlic juice processing by-products can serve as useful feed additives in formulated diets for aquaculture fish production.