No abstract

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.

Optimal larviculture techniques have yet to be established for Pacific cod (Gadus macrocephalus), particularly in relation to the nutritional quality of live prey. Elevated mortality during early life stages is a major concern during the production of Pacific cod larvae; this seems to be related to, among other things, nutritional deficiency during the early feeding stage, particularly the quantities and proportions of highly unsaturated fatty acids in live food. With the aim of improving the growth and survival of larval Pacific cod while also determining the optimum level of dietary docosahexaenoic acid (DHA), we investigated the effects of four levels of dietary DHA (0%, 3%, 6%, and 9% of total fatty acids [TFAs]) on the growth, survival, and tissue fatty composition of larvae. The actual DHA concentrations of the diets were 0.22%, 3.09%, 5.88%, and 9.28% of TFAs for D1, D2, D3, and D4 diets respectively. From 43 to 64 days post hatch, larvae were fed the experimental diets. Larvae fed D3 diet had the highest survival rates, total length, and total weight at the end of the feeding trial. The fatty acid composition of the whole larval body reflected the corresponding dietary composition. Overall, these results suggest that a DHA level of 4.85%–8.50% of TFAs is optimal in the diet of larval Pacific cod during Artemia feeding.

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.

No abstract