Utilization of fish waste biomass as a fishmeal alternative in European seabass (Dicentrarchus labrax) diets: effects on immuno-competence and liver and intestinal histomorphology

The potentiality of using two novel aqua-derived meals from fish waste biomass in either non-fermented (FW) or fermented (FFW) form as dietary fishmeal (FM) substitutes for juvenile European seabass, Dicentrarchus labrax, (IBW, 29 g) was investigated. FW meal (40% crude protein, 20% lipids, and 7.5% ash) was fermented using the marine fungus, Beauveria bassiana. The influence of partial substitution of dietary FM using either FW or FFW meal at, 15%, 30%and 45% levels, on fish immunity and liver and intestinal histomorphology was examined to determine the appropriate form and optimal inclusion level of each. Fish were fed a basal control diet and six test diets containing either FW or FFW, each at the three FM substitution levels, for 90 d. Results showed that total serum protein, albumin, globulin, phagocytic activity of leucocyte, respiratory burst and lysozyme activities, and immunoglobulin M were all significantly improved in fish consumed the FW diet, at all incorporation levels than the other diets. Intestinal and liver histology were also examined for any morphological alteration. Fish liver integrity remained unchanged using diet composition, with no signs of inflammation. Morphology of proximal, mid, and distal intestines via light and electron microscopy illustrated that seabass fed the FW30 diet had the best gut structure. Meanwhile, administration of the highest dietary FW/FFW level (45% FM) induced some inflammatory signs in the proximal intestinal mucosa of seabass. These findings suggest that FW meal is a feasible alternative for replacing 30% of FM in the seabass diet without compromising immunity and liver or intestinal integrity.