The impact of diet & temperature on yellowtail kingfish health & microbiome

Negative health outcomes related to plant-based proteins remain a barrier to effective fishmeal replacement in farmed carnivorous fish such as Yellowtail Kingfish (Seriola lalandi). Here, farmed Yellowtail Kingfish housed at optimal and non-optimal temperatures (22 and 26°C) were fed a fishmeal diet (FM) or a FM diet partially replaced with soy-protein concentrate (SPC) to investigate impacts on host health and microbial community composition within skin mucosa, gut mucosa and digesta. The combination of SPC and elevated temperature significantly reduced weight gain and measured digesta myeloperoxidase and increased plasma lysozyme levels. Skin microbial communities were distinct from and more diverse than the gut and digesta microbiomes, which both had low diversity. The overall microbial composition and relative abundance of specific OTUs were significantly impacted by SPC and elevated temperature. The SPC diet and elevated temperature were both associated with significantly increased levels of an OTU identified as Photobacterium in the digesta and skin. Increased relative abundance of Photobacterium was also significantly correlated with reduced levels of digesta peroxidase, an innate immunity defence mechanism. The shifts in the microbial communities and the increase in Photobacterium reveal the importance of considering the microbiome in future efforts to replace fishmeal in Yellowtail Kingfish diets.