Effects of Short-Term Feeding with Diets Containing Insect Meal on the Gut Microbiota of African Catfish Hybrids

The impact of short-term feeding of three distinct diets containing insect meals on the intestinal microbiota of African catfish hybrid (<i>Clarias gariepinus × Heterobranchus longifilis</i>) juveniles was examined. The animals received experimental diets containing 30% insect meals derived from black soldier-fly larvae (BSL) (<i>Hermetia illucens</i>), yellow mealworm (<i>Tenebrio molitor</i>) or blue bottle-fly larvae (<i>Calliphora vicina</i>) for 18 days. The relative abundance of the <i>Bacillaceae</i>, the <i>Planococcaceae</i> and other bacteria significantly increased (<i>p</i> < 0.05) in the intestinal microbiota of the BSL group and also in the pooled group of the three catfish groups that received insect meals. Several strains of the <i>Bacillales</i> cultured from BSL feed had higher (<i>p</i> < 0.05) abundance in the intestinal microbiota of the BSL group compared to those of the control group. Among these <i>Bacillales</i> strains, a single <i>fosB</i> antibiotic resistance gene was identified. In the gut resistomes of both the BSL and the control catfish groups, the <i>tetA(P)</i>, <i>tetB(P)</i> and <i>lnu(C)</i> antibiotic-resistance determinants were detected, while <i>fosB</i> was detected only in the BSL group. Overall, the study showed that a short-term shift to diets containing insect meals can induce significant (q < 0.05) changes in the gut microbiota of the African catfish without the development of reduced α-diversity and without the overgrowth of bacteria pathogenic to fish.