Black Soldier Fly larvae meal (Hermetia illucens; BSFLM) is emerging as a sustainable and functional alternative to fishmeal in aquaculture diets. This study investigated the effects of graded dietary inclusion levels of defatted BSFLM on the gut microbiome of Atlantic salmon (Salmo salar ) at two critical ontogenetic stages: first feeding and smoltification. Fry were fed diets containing 0%, 8%, 16%, or 24% BSFLM for 21 days during the first feeding stage, while pre-smolts received diets with 0%, 5%, or 15% BSFLM during smoltification. Microbial communities from the gut, feed and water were characterised using 16S rRNA gene amplicon sequencing, incorporating a novel titration-based quantification step to enhance library preparation accuracy.
Results highlighted that BSFLM inclusion during the first feeding significantly modulated gut microbiome composition, with distinct community structures observed across diets (Figure 1; PERMANOVA, p = 0.001). BSFLM diets were associated with increased microbial richness and evenness, suggesting enhanced diversity during early gut colonisation. Taxonomic profiling further revealed diet-specific shifts in the relative abundance of key bacterial taxa.
During smoltification, BSFLM inclusion also altered the gut microbiome , with all insect meal diets exhibiting consistently higher microbial richness compared to the control. Taxonomic analyses revealed diet- and time-dependent shifts in microbial composition, reflecting dynamic restructuring of the gut microbiome throughout smoltification.
These findings demonstrate that BSFLM not only serves as a sustainable alternative to fishmeal but also exerts stage-specific modulatory effects on the gut microbiome of Atlantic salmon, with potential implications for fish health and performance.