Manipulation of Graded Levels of Jack Mackerel Meal in Diets Replacing Fish Meal with Corn Protein Concentrate in the Diets of Rockfish (Sebastes schlegeli): Effects on Growth Performance, Feed Utilization, and Economic Analysis

Incorporating protein feed ingredients that exhibit strong attractiveness to the target fish species is an effective and sustainable feeding strategy to improve feed intake and enhance growth performance. An 8-week feeding experiment was performed to elucidate the manipulation impact of graded levels of jack mackerel meal (JMM) in diets replacing 10% fish meal (FM) with corn protein concentrate (CPC) on the growth, feed utilization, and blood chemistry of rockfish (Sebastes schlegeli), as well as to perform an economic analysis. A total of 450 fish were randomly assigned to 15 plastic tanks (30 juveniles/tank). Five experimental diets were formulated to be isoproteic (50.0% crude protein) and isolipidic (15.5% crude lipid). The control (Con) diet contained 55% FM. In the Con diet, 10% of the FM was substituted with CPC, and graded levels of JMM at 0%, 20%, 40%, and 60% were subsequently incorporated instead of the FM, referred to as CPCJ0, CPCJ20, CPCJ40, and CPCJ60, respectively. Triplicate groups of rockfish were carefully hand-fed the diets to satiation throughout the feeding experiment. The rockfish fed the CPCJ60 diet produced significantly higher weight gain (WG) (p < 0.002) and specific growth rate (SGR) (p < 0.003) than those fed the Con, CPCJ0, and CPCJ20 diets but showed no significant (p > 0.05) differences compared to those fed the CPCJ40 diet. Both the WG (Y = 0.9367X + 17.0500, p < 0.0001, Adjusted R2 = 0.8468) and SGR (Y = 0.0005X + 0.0165, p < 0.0001, Adjusted R2 = 0.8580) of the rockfish increased linearly with increased dietary JMM inclusion levels when 10% of the FM was replaced by CPC. The rockfish fed the CPCJ60 diet showed a significantly higher feed consumption (FC) (p < 0.03) compared to those fed the CPCJ0 diet. Among the dietary treatments, however, no significant (p > 0.05) differences were found in the feed utilization, proximate composition, amino and fatty acid profiles, and blood chemistry of the rockfish. The CPCJ60 diet resulted in the highest economic profit index (EPI) among the dietary treatments. Conclusively, JMM was found to be effective in improving the FC of rockfish fed the diets replacing 10% of the FM with CPC. Furthermore, the WG and SGR of the rockfish fed the diets replacing 10% of the FM with CPC improved linearly with elevated JMM inclusion. Thus, incorporating 60% of JMM into the diets substituting 10% of the FM with CPC was the most recommended strategy according to the growth performance and FC of the rockfish, providing the highest EPI for fish farmers.