Evaluation of Wasted Tofu Meal as an Alternative to Fish Meal in Juvenile Yellowtail, Seriola quinqueradiata

A six-week feeding experiment was carried out to investigate the suitability of wasted tofu meal (WTM) as a substitute protein source for fish meal (FM) in diets for juvenile yellowtail (Seriola quinqueradiata). A diet containing FM as the principal protein source served as the control (C), while WTM was incorporated to replace 20%, 35%, and 50% of the FM protein in the experimental diets, referred to as T20, T35, and T50, respectively. Juvenile fish with an initial average body weight of approximately 30.99 g were randomly distributed into 500-L tanks at a density of 20 fish per tank, with triplicate groups assigned to each dietary treatment. At the end of the feeding trial, fish fed the T20 diet showed no significant differences from the control group in final body weight, specific growth rate, daily feed intake, feed efficiency, or survival. However, fish receiving the T35 and T50 diets exhibited significant reductions in most growth performance indices compared with those fed the control diet. Although nutrient retention efficiency and plasma biochemical indicators associated with fish health were not significantly influenced by dietary treatment, alterations were observed in whole-body lipid composition and fatty acid profiles, including reductions in EPA, DHA, total n-3 fatty acids, and the n-3/n-6 fatty acid ratio with increasing WTM inclusion. Overall, the findings suggest that, under the dietary formulations tested, WTM can replace up to 20% of FM protein in diets for juvenile yellowtail without negatively affecting growth performance or physiological health; however, supplementation with n-3 HUFA-rich lipid sources may be required to maintain optimal whole-body fatty acid composition and product nutritional quality.