The effect of dietary fish oil replacement by microalgae on the gilthead sea bream midgut bacterial microbiota

Abstract

The aim of this work was to evaluate the effects of dietary microalgae blends as fish oil replacers οn the midgut bacterial microbiota of gilthead sea bream (Sparus aurata). The control diet (FO) contained only fish oil as source of lipids, EPA and DHA fatty acids, while three experimental diets were used where fish oil was replaced at 67% by one of the following microalgae biomass blends: Michrochloropsis gaditana and Isochrysis sp. (MI), Phaeodactylum tricornutum and Isochrysis sp. (PI) and Schizochytrium sp. and P. tricornutum (SP). The midgut bacterial community composition and the dominant OTUs indicated that the sea bream midgut bacterial communities were altered compared to the control feed. Additional evidence from the presumptive bacterial functional pathways suggests that the microalgal-containing aquafeed resulted in one overexpressed and one underexpressed pathway. The overexpressed pathway was related to the metabolism of fucose, a major carbohydrate of these microalgae species. This suggests that a new gut microbiota profile was selected because of the microalgae inclusion in the provided aquafeed. All these data combined with the absence of mortality in fish, shows that the gilthead sea bream gut microbiome can smoothly adapt its function according to the metabolic capacity of the microalgae combinations that we used. The MI feed seems to promote several beneficial bacteria with potential probiotic abilities in the fish gut.