Vegetable oil blends and environmental temperature influence the nutrient efficiency and gut microbiome of rainbow trout: Insight on microbial diversity, community structure, and function

The unsustainability and high cost of animal-based diets have increased production in the aquaculture industry, especially for carnivorous fishes like rainbow trout. This has forced farmers and researchers to look for alternatives which include the use of plant-based components. Hence, the present study evaluated the influence of dietary administration of fishmeal and vegetable oil blends (palm, camelina, and canola oil) and variation in environmental temperature on the nutrient utilization and intestinal microbiota of rainbow trout (Oncorynchus mykiss). Our findings demonstrated a significant impact (P < 0.05) of dietary composition and temperature regimens on various nutrient efficiency parameters, including protein productive value (PPV), protein efficiency ratio (PER), lipid efficiency ratio (LER), energy productive value (EPV), and energy efficiency ratio (EER). Notably, LER was significantly influenced by dietary composition alone. 16S rRNA analysis showed that both microbial composition and diversity were affected by temperature variations while dietary composition remained stable. Taxonomic composition showed high abundance of Firmicutes, Fusobacteriota, and Proteobacteria phylum under diet and temperature conditions, with Mycoplasmataceae, Fusobacteriaceae, and Enterobacteriaceae identified as the predominant families. Fusobacteria were highly enriched at higher temperatures (18 °C and 20 °C) and reduced at lower temperatures (14 °C). Microbial functional analysis demonstrated a significant enhancement of pathways related to energy metabolism for fish fed diet 2 and propanoate metabolism for those reared at 18 °C. We infer that the combination of fishmeal and vegetable oil blends enhances nutrient retention utilization and energy metabolism in rainbow trout at elevated temperature.