Different studies have shown that insect meals can partially or completely replace the fish and soya bean meals that are commonly used in aquaculture. However, information is lacking on the amino acid and fatty acid contents and digestibility of different insect meals. Moreover, we evaluated different proportions of insect diets and determined how these affected the nutritional values of insect meals. Our purpose was to clarify these aspects and consider the availability of protein, amino acids, lipids and fatty acids in insect meals in fish nutrition. Generally, insect meals have higher indispensable amino acid contents than other meal types, with contents closely related to those in fish meal. Insect meal can be an important source of essential amino acids such as methionine, with contents ranging between 0.47 and 4.03 g 100 g À1 sample. These values are higher than those reported for other animal and plant meals. In addition, insects are also good sources of lipids and fatty acids, and the amounts and types of fatty acids vary according to the species, stage of development and type of feed. Moreover, the additional nutritional value of insect meal includes compounds such as chitin, which is primarily considered a fibre but also contains nitrogen and amino acids. Insect peptides with activity against pathogenic microflora provide secondary biological effects, which may significantly improve animal health.

Background Insects in the fish diet are a natural source of protein, fat, and other nutrients. These meals are considered an ecological replacement for fishmeal to improve growth parameters. The application of insect meals to fish diets has been studied, especially in continental fish. Data regarding the effects of insect meals on the gut health of Siberian sturgeon are not available. This study investigated the effects of full-fat Hermetia illucens (HI) and Tenebrio molitor (TM) meals on the gut health of juvenile Siberian sturgeon. Growth performance, gastrointestinal tract (GIT) histomorphology and the microbiome composition of juvenile Siberian sturgeon were analyzed. Results The inclusion of insect meals did not affect the growth performance or the survival rate. In the gastrointestinal tract histomorphology, a reduction in the mucosa thickness with the HI treatment was observed. In contrast, fish fed the TM diet had an increase in the thickness of the muscular layer. There were no observed significant differences in villus height among treatments. The analysis of the selected microbiota populations in the Siberian sturgeon gastrointestinal tract showed that insect addition affected the composition of the microbiome. The greatest effect on bacterial populations (Clostridium leptum subgroup, Enterobacteriaceae, Clostridium coccoides – Eubacterium rectale cluster, Aeromonas spp., Bacillus spp., Carnobacterium spp., Enterococcus spp. and Lactobacillus group) was observed with the HI diet (P < 0.05). The TM-based diet increased counts in the following bacterial groups: Clostridium coccoides – Eubacterium rectale cluster, Bacillus spp., Carnobacterium spp., and Enterococcus spp. In contrast, the TM diet decreased the total number of bacteria. The TM diet did not significantly affect the Clostridium leptum subgroup, Enterobacteriaceae, Aeromonas spp. or the Lactobacillus group. Conclusions Fish meal replacement by the inclusion of 15% of full-fat Hermetia illucens and Tenebrio molitor (15%) meals did not affect the growth performance, survival rate or villus height of juvenile Siberian sturgeon. The present study suggests that an H. illucens-based diet positively affects the gut microbiota composition and intestinal morphology of juvenile Siberian sturgeon without negative changes in the villus height.

a 71-day-long experiment was conducted to evaluate the inclusion of 20% hermetia illucens (hi) meal; Tenebrio molitor (Tm) meal; Gryllodes sigillatus (gs) meal; and Blatta lateralis (bl) meal in comparison to a control diet without any insect-based materials that used fish meal as the main source of protein. a total of 1950 rainbow trout juveniles (53.39 ± 3.74 g) were used. The formulated diets were isonitrogenous (45%) and isoenergetic (10 mJ kg -1 ). The inclusion of a full-fat insect meal did not affect the survival rate during the experimental period. The growth performance was significantly improved in the BL and TM treatments, while in the HI treatment was not affected. however, the gs treatment had a negative effect on the growth performance. The villus height decreased in the Tm and gs treatment groups and increased in the bl diet group. The total number of bacteria increased in all insect meal diet groups. The results of the experiment show that B. lateralis, T. molitor and h. illucens full-fat meals can be used as a partial fish meal replacement without negative effects on survival or growth performance parameters. moreover, full-fat insect meals may be considered as a protein source and a functional feed component that may positively affect the histomorphological structure of the fish gastrointestinal tract and stimulate the expansion of beneficial bacterial populations in the gut.

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