Effects of Three Feed Additives on the Culturable Microbiota Composition and Histology of the Anterior and Posterior Intestines of Zebrafish (Danio rerio)

SIMPLE SUMMARY: This work is dedicated to the study of the effects of three feed additives that are promising for use in aquaculture on the culturable microbial community and the tissue structure (histology) of the intestines of laboratory zebrafish. The feed additives used in this research have different functional properties: (i) micronutrient chelated compounds, which eliminate mineral nutrition deficiencies; (ii) butyric acid, a postbiotic drug aimed at stimulating intestinal bacteria growth and improving immunity; and (iii) lycopene, a carotenoid and wide-spectrum antioxidant. All of the tested supplements resulted in changes in the intestinal microbial community in both the anterior and posterior intestines. The change in gut microbiota correlated with histological changes in the intestines. The results of the study showed that in most concentrations, the feed additives had a positive effect on certain groups of microorganisms. The method of microbiota research based on microorganism cultivation used in this work makes it possible to evaluate the effect of feed additives on the relative abundance of key representatives of the microbial community. ABSTRACT: In this study, the effect of three promising feed additives (chelated compounds of trace elements, butyric acid, lycopene) on changes in the culturable microbiota and histological parameters of two sections of the intestines of Danio rerio (zebrafish) was studied. The use of these feed additives can help to eliminate the deficiency of trace elements, modulate the composition of the microbiota due to the postbiotic properties of butyric acid, and reduce oxidative stress when using lycopene. Incorporation of the investigated supplements in the feed resulted in a significant change in the relative abundance of certain groups of microorganisms. The taxonomic diversity of cultured microorganisms did not differ in the anterior and posterior intestines, while there were differences in the relative abundance of these microorganisms. The most sensitive groups of microorganisms were the genera Bacillus and Serratia. A significant effect on the composition of the cultured microbiota was caused by lycopene (in all studied concentrations), leading to a significant increase in the relative abundance of Firmicutes in the anterior gut. Studies of the histological structure of the anterior and posterior guts have shown the relationship between the barrier and secretory functions of the gut and the composition of the microbiota while using butyric acid (1 and 2 g kg(−1)) and trace element chelated compounds (2 mg kg(−1)). This culture-dependent method of studying the microbiome makes it possible to assess changes in some representatives of the main groups of microorganisms (Firmicutes and Proteobacteria). Despite the incompleteness of the data obtained by the culture-dependent method, its application makes it possible to assess the bioactive properties of feed and feed additives and their impact on the microbiota involved in digestive processes.