Black Soldier Fly Meal as a Gastrointestinal Tract Microbiota Remodelling Factor: A New Natural and Sustainable Source of Prebiotic Substances for Fish?

The microbiota of the gastrointestinal tract (GIT) plays a crucial role in the development, lifespan, physiology, barrier functions and immunity against pathogens in fish. One of the significant causes of fish mortality in production systems, which also generates huge financial losses, is pathogenic dieseases. Consequently, effectively managing disruptions in the microbiota could play a crucial role in mitigating economic losses across the sector. It was investigated the effect of an alternative raw material increasing inclusion—full-fat Hermetia illucens larvae meal on the composition of the gastrointestinal microbiome of Atlantic salmon. Thus, five experimental feeds were prepared: a control diet (CON) without the addition of black soldier fly full-fat meal (BSFM) and with 30% fish meal (FM); BSFM5, with 5% addition of full-fat BSFM and 27.1% FM; BSFM10, with 10% full-fat BSFM and 24.3% FM; BSFM15, with 15% addition of full-fat BSFM and 21.3% FM; and BSFM20, with 20% addition of full-fat BSFM and 18.6% FM. After 60 days of growth experiment on Atlantic salmon presmolts, the contents of two sections of the GIT, proximal and distal, were gently sampled and subjected to next-generation sequencing (NGS) to analyse the microbial populations. No significant differences were observed in the microbial compositions of the groups, irrespective of the intestinal section analysed. In the proximal and distal intestine, the CON group exhibited the highest number of distinct phyla. Increasing the inclusion of BSFM in the diet led to a reduction in the abundance of specific phyla. Similar results were noted at genus level. The BSFM5 and BSFM10 groups showed increase number in Enterococcus, while the Lactobacillus population were maintained at a high level. Due to abovementioned changes as well as the increased share of Bacilli populations, it may be concluded that up to 20% BSFM shares may have positive microbiota-modulating effects. Thus, BSFM may be considered not only as a nutrient source but a functional feed material in fish diets also, due to its prebiotic effects observed in the study.