Substitution Impact of Tuna By-Product Meal for Fish Meal in the Diets of Rockfish (Sebastes schlegeli) on Growth and Feed Availability.

Simple Summary: Fish meal is commonly used as the main protein source in aquafeeds. However, the increasing global demand and the overfishing of wild fish stocks commonly used as fish meal sources have restricted supply and increased the price of fish meal in recent decades. To achieve the goal of sustainable fish culture, fish meal replacement with an alternative source that is inexpensive and year-round available in aquafeeds is highly needed. Meanwhile, more than half of the total tuna is trashed as waste in tuna-canning processing plants. In the current study, we investigated the dietary substitution effect of fish meal with tuna by-product meal on growth, feed availability, and biochemical composition of the early stage of juvenile rockfish, one of the most widely farmed marine fish species in Eastern Asia. The results indicated that up to 40% of fish meal could be substituted with tuna by-product meal in the diets of rockfish without negatively influencing the growth, feed availability, and hematological parameters of rockfish. With the dietary replacement of 40% fish meal with tuna by-product meal in practical feeding, rockfish farmers are able to produce the highest economic return. This experiment was performed to assess the substitution impact of fish meal (FM) with tuna by-product meal (TBM) in feeds on growth and feed availability of the early stage of juvenile rockfish (S. schlegeli). Six experimental feeds were prepared to be isonitrogenous and isolipidic. Fifty-five percent of FM was contained in the control (Con) diet. In the Con diet, 20, 40, 60, 80, and 100% FM were replaced by TBM, named the TBM20, TBM40, TBM60, TBM80, and TBM100 diets, respectively. A total of 540 early-stage juvenile rockfish averaging 2.4 g was divided into 18 tanks and hand-fed to satiation for 56 days. Weight gain and feed consumption of rockfish fed the TBM20 and TBM40 diets were comparable to rockfish fed the Con diet. The specific growth rate (SGR) of rockfish fed the Con diet was comparable to rockfish fed the TBM20, TBM40, and TBM60 diets. Feed efficiency, biometric indices, hematological parameters, proximate composition, and amino acid profiles of rockfish were not impacted by dietary treatments. The economic profit index (EPI) of the Con, TBM20, and TBM40 diets were higher than that of all other diets. FM up to 40% could be substitutable with TBM in the diets of rockfish without deteriorating weight gain and feed consumption, but producing the highest EPI. [ABSTRACT FROM AUTHOR]