Plant-derived feed additives provide cost effective and environmentally friendly alternatives to antibiotics for improving fish performance in aquaculture. An 8-week feeding trial was conducted to evaluate the effects of dietary ginger residue from juice extraction (GRJE) on juvenile black rockfish (Sebastes schlegelii) growth performance, antioxidant enzyme activities, and resistance to Streptococcus iniae infection. Juvenile rockfish (n = 450; initial weight = 2.2 ± 0.01 g) were randomly distributed into 30 L rectangular tanks (30 fish per tank). Five experimental diets with GRJE concentrations of 0% (control), 0.25%, 0.5%, 0.75%, and 1% were prepared in triplicate. Three groups of fish were randomly assigned to each diet and fed to apparent satiation twice daily. After the feeding trial, fish were challenged with S. iniae, and cumulative survival was observed for six days. Growth parameters, feed efficiency, and the protein efficiency ratio showed a quadratic correlation with the GRJE concentration in the fish diet. Proximate composition and plasma chemistry were not significantly affected. Plasma lysozyme, superoxide dismutase, glutathione, and catalase activities linearly increased with increasing GRJE supplementation levels. Moreover, survival in the S. iniae challenge test was significantly higher in fish fed diets supplemented with 0.75–1% GRJE. Our findings demonstrated that 0.75% GRJE dietary supplementation enhanced the growth performance, antioxidant activity, and disease resistance of juvenile black rockfish with no adverse effects.

An 8-week feeding trial was conducted to evaluate the effects of various dietary levels of garlic juice processing waste (GJPW) on the growth, feed utilization, digestive and antioxidant enzyme activity, growth- and antioxidant-related gene expression, and resistance to Streptococcus iniae infection of juvenile black rockfish (Sebastes schlegelii). A total of 450 juvenile rockfish were randomly distributed into 30 L rectangular tanks (30 fish per tank). Five experimental diets were prepared in triplicate. The fish were fed experimental diets supplemented with GJPW at concentrations of 0 (GJPW0, control), 2.5 (GJPW2.5), 5 (GJPW5), 7.5 (GJPW7.5), and 10 g kg⁻¹ (GJPW10) diet. All of the GJPW-supplemented treatments (2.5, 5, 7.5, and 10 g kg⁻¹) significantly enhanced weight gain (WG), specific growth rate (SGR), feed efficiency (FE), protein efficiency ratio (PER), and digestive enzyme activity (amylase, trypsin, and lipase). A decreasing trend was seen in plasma aspartate aminotransferase (ALT), alanine aminotransferase (AST), and glucose (GLU) content with increasing dietary levels of GJPW. In contrast, plasma lysozyme and antioxidant enzyme activities were significantly increased with increasing dietary GJPW levels. Furthermore, GJPW administration significantly upregulated the expression of insulin-like growth factor-1 (IGF-1), superoxide dismutase (SOD), catalase (CAT), and glutathione S-transferase (GST) in the liver of rockfish. A challenge test with S. iniae showed significantly higher resistance in the GJPW-supplemented treatments than in the control. In short, dietary supplementation GJPW enhanced growth performance and antioxidant response in juvenile black rockfish, with suitable effects in fish fed with 2.5 g kg⁻¹ GJPW for 8 weeks.

This study evaluated bioactive compounds in blood orange (Citrus sinensis (L.) Osbeck) peel (BOP) as dietary additives. An 8-week feeding trial was conducted to investigate the effects of dietary supplementation on the growth performance, body composition, digestive enzyme activity, antioxidant capacity, and immune response of juvenile black rockfish. A total of 1260 juvenile rockfish (1.4 ± 0.01 g) were randomly distributed into seven treatment groups, each with 50 fish per circular tank. The groups were fed seven different diets containing graded levels of 0 (control, BOP0), 1 (BOP1), 2 (BOP2), 3 (BOP3), 5 (BOP5), 7 (BOP7), and 10 (BOP10) g kg⁻¹, respectively. The BOP10 diet significantly enhanced the final weight, weight gain, specific growth rate, protein efficiency ratio, and protein retention in fish. The BOP treatments notably affected the fishes’ whole-body crude protein and lipid contents. Plasma total cholesterol levels of fish fed the BOP0 and BOP1 diets were significantly higher than those fed the BOP7 and BOP10 diets. The activities of trypsin and lipase were significantly affected by dietary BOP levels. The antioxidant enzyme activity in the plasma of fish fed the BOP10 diet was significantly higher than those fed the BOP0 diet. The lysozyme activity and levels of immunoglobulin M and G in fish fed the BOP0 diet were significantly lower than those in fish fed the BOP10 diet. In conclusion, dietary supplementation of BOP at 10 g kg⁻¹ improved the growth performance and overall health of juvenile black rockfish.