Bioconversion of fish-wastes biomass into a fish meal alternate for European seabass (Dicentrarchus labrax) diets

The effect of replacing fish meal (FM) in juvenile European seabass (Dicentrarchus labrax) diets with fish wastes (FW) and fermented FW (FFW) by marine fungus Beauveria bassiana was investigated. Seven diets were prepared: control (CTRL) and six diets containing either FW or FFW to substitute FM at 15, 30 and 45% (FW15/FFW15, FW30/FFW30 and FW45/FFW45 each in turn). Fish (initial weight Ca. 30 g) were reared for 90 days in 21 PVC tanks (3 m3) and fed to apparent visual satiation. The recorded values for growth, feed utilization efficiency, survival rate and amino acids composition of fish fed either FW or FFW diets, at all tested levels, are not significantly different relative to those values of control group. Carcass protein content was not influenced by diet, but lipid content of FW45 and FFW45-fed fish showed a significant elevation relative to that of other fish groups. Blood parameters indicate an improvement in general health status and both liver and kidney function of FW-fed fish up to 30% FM replacement level, relative to those of CTRL and FFW-fish. Fish fed the FW-diets showed higher fungal and acid fermentative bacterial counts and lower count of Vibrio spp. and coliform, suggesting better gut health as compared to FFW-fed fish. These results indicate that 30% of dietary FM can be replaced with FW meal without adverse effects on fish growth performance, feed utilization, general health status or intestinal microbiome and fermentation with B. bassiana has some negative influence on gut integrity at 45% FM substitution level.