Rapid increase in global presence of antibiotic residues in the sea water triggers antimicrobial resistance that impairs both the ability to cure fish in aquaculture, and consumer safety. Faced by a high demand for fish protein destined for human consumption and production of aquafeed, the conventional aquafeed industry is becoming unsustainable. The use of alternative protein sources and health-promoting additives, such as insect-derived proteins and probiotics, has beneficial effects on fish health, although the involved mechanisms are largely unknown.
We have performed a six-month field trial on the Sparus aurata; fish were fed three diets, either insect-supplemented (Hermetia illuscens), insect-supplemented plus autochthonous intestinal Bacillus spp. or standard diet (control). Samples of anterior intestines were analyzed in three timepoints for the microbiome (16s MiSeq), ultrastructure (TEM), and gene expression (qPCR S. aurata array of 44 selected markers of intestinal function and integrity, nutrient transport, and immune response).
Intestinal epithelium of all groups did not show any obvious signs of degeneration or inflammation. Main changes in microbiome composition occurred within the first month of the treatment. 17 epithelial integrity and immune response genes were differentially expressed among diets. Many of them were upregulated with the insect diet, and the upregulation was even enhanced with the probiotic diet. Probiotics also repressed the inflammatory/immune-regulatory genes that were upregulated by the insect diet.
In conclusion, the insect diet combined with probiotics can be beneficial for the preservation of homeostasis and innate immunity in fish, and importantly, does not negatively affect product biomass.