Influence of feeding black soldier fly (Hermetia illucens), cricket (Gryllodes sigillatus), and superworm (Zophobas morio) on the gut microbiota of rainbow trout (Oncorhynchus mykiss).

Aim: This study investigates how replacing fishmeal and fish oil with insect meals in feed impacts the gut microbiota in rainbow trout (Oncorhynchus mykiss), a crucial species in aquaculture.

Methods and results: Dietary inclusion of black soldier fly (Hermetia illucens), cricket (Gryllodes sigillatus), and superworm (Zophobas morio) were evaluated for their impact on intestinal microbial diversity and community composition following a 12-week feeding trial. Fish were fed one of four isonitrogenous and isoenergetic diets: a control diet without insect meal, and diets with 15% defatted black soldier fly meal, full-fat adult cricket meal, or full-fat superworm meal. The microbiota of intestinal digesta and fish feed was characterized using 16S rRNA gene sequencing on the Illumina MiSeq platform. Results revealed significantly lower alpha diversity indices in the cricket treatment compared to the control. Beta diversity analysis showed Bacillota as the dominant phylum across all treatments, with the initial stock population richer in Mycoplasmatota. A novel genus within Mycoplasmataceae was prevalent at day 0 and in all treatments. Black soldier fly meal increased an unidentified Peptostreptococcaceae genus (bsv123) compared to control and superworm diets, while cricket meal elevated Streptococcus levels.

Conclusions: Insect-based diets, particularly with black soldier fly meal, significantly alter beta diversity within the gut microbiota of rainbow trout, with cricket meal reducing alpha diversity and superworm having minimal impact.