The effects of organic protein supplementation upon growth, feed conversion and texture quality parameters of juvenile cobia (Rachycentron canadum)

An eight week feeding trial was conducted to examine the impacts of organically certifiable alternate protein sources on growth, feed efficiency, biological indices, fillet proximate composition and fillet quality in juvenile cobia. Diets were formulated to be isonitrogenous and isocaloric. The control diet provided 45% crude protein from Special Select® menhaden fish meal and 10% total lipid. The remaining diets were formulated with 25 and 40% inclusion of NuPro® (an organically certified yeast-derived protein source), and 40% inclusion of organically certified soybean meal, soybean isolate, or hemp seed meal. Two additional diets were formulated to contain a mixture of all organic protein sources at 23% with 8% fish meal or 25% and no fish meal. Diets were fed to triplicate groups of juvenile cobia (initial weight 10 g/fish) in 300 L circular tanks connected as part of a recirculating aquaculture system. Weight gain ranged from 167 to 1138% increase from initial weight and was similar for all fish fed diets containing 40% of any given alternate protein source. Fish fed the blended diet with 8% fish meal exhibited significantly lower weight gain, SGR, and FE ratio values than all other fish. Cobia fed the diet without any fish meal did not survive to the end of the study. Biological indices such as muscle ratio (MR), visceral somatic index (VSI), and packed cell volume (PCV) were all similar between fish fed the control diet and those fed diets with up to 40% alternate protein. Fish fed the diet with only 8% fish meal had significantly lower MR, PCV, and plasma protein, and significantly higher VSI. All fish exhibited similar fillet proximate composition for protein, lipid, dry matter, and ash except for those fed the diet containing 8% fish meal. Alternate protein source did appear to impact the fillet texture of cobia. Generally speaking, plant protein sources returned higher textural characteristics than the fish meal control. At all time points and all texture parameters, cobia fed the diet containing hemp seed meal returned the highest values except for distance to rupture in the final time point. Results indicate that up to 40% fish meal protein can be replaced by any of the organically certifiable alternate proteins that were used in this study without detrimental impacts to weight gain, feed efficiency, biological indices, or fillet composition in juvenile cobia. Our results also suggest that alternate proteins have differential effects upon final product quality, which may have implications in terms of cobia processing and development of industrial products.