A sustainable growth of the aquaculture sector implies the use of sustainable novel raw materials as replacement of the traditional fish meal (FM) and fish oil (FO) ingredients. This fact will lead to the development of functional diets as part of a management strategy to reduce the effects on fish growth performance and health derived from low FM/FO dietary contents. In this sense, krill meal (Euphausia superba ) may be a potential candidate to potentiate fish growth and health status.
European sea bass (Dicentrarchus labrax) were fed a commercial r elevant diet with either a 15% fishmeal content (KM0 ) or the same diet substituted by 30 % (KM5) or 50% Antarctic krill meal (KM7.5) for 12 weeks in triplicates . Diets were isoproteic (45%) and isolipidic (18%).
At the end of the feeding trial, growth performance, liver morphology, liver proximate composition and fatty acid profile, as well as liver lipid metabolism related genes were evaluated. After two months of supplementation, krill meal- supplemented fish presented increased feed intake (p<0.05), regardless of the dietary level. However, feed conversion ratio (FCR) was only significantly lower (p<0.05) in fish fed the KM7.5 diet. At the end of the feeding trial, fish fed KM- based diets presented increased (p<0.05) final weight, final length, relative growth, specific growth rate (SGR) and improved FCR, irrespective of the KM dietary level. Livers of European sea bass fed the experimental diets presented similar (p>0.05) biochemical composition and fatty acid profile. Despite the similar content of liver lipids, fish fed KM diets presented a healthier liver morphological profile. Hepatocytes of KM fed fish presented lower vacuolization levels , better alignment of the hepatocyte nuclei along the sinusoidal lines, and in general lower sings of steatosis. Liver g ene expression results revealed a down regulation of the 3 -hydroxy-3-methylglutaryl-coenzyme A reductase (hmgcr) and delta-6-desaturase (fads2) expression, when fish were fed the KM7.5 diet compared to fish fed the KM0 diet. Besides, a significant negative correlation between the gene expression le vels of hmgcr , fads2 and KM dietary levels were observed. On the other side, fatty acid binding protein 7 (fabp7 ) and KM were significantly positively correlated.
Altogether profiling KM as a potential growth and health promoter in European sea bass fed low fish meal and oil diets.