Aims The aim of this work was to study the gut microbial diversity from eight species of wild fish with different feeding habits, digestive physiology (gastric vs. agastric) and provide comparative structural analysis of the microbial communities within their environment (food items, water, sediments, and macrophytes). Methods and Results The microbiota of fish gut and their prey items were studied using next generation high‐throughput sequencing of the 16S ribosomal RNA genes. A scatter plot based on PCoA scores demonstrated the microbiota formed three groups: 1) stomach and intestinal mucosa, 2) stomach and intestinal content, and 3) prey and environment. Comparisons using ANOSIM showed significant differences among intestinal content of omnivorous, zoobenthivorous, zooplanktivorous‐piscivorous fishes (p ≤ 0.1). No significant difference was detected for mucosa from the same groups (p > 0.1). Conclusions Neither the interspecies differences in fish diet nor their phylogenetic position had any effect on the microbiome of the intestinal mucosa, but diet did influence the composition of the microbiota of the intestinal content. Significance and Impact of Study The data demonstrate that fish harbored specific groups of bacteria that do not completely reflect the microbiota of the environment or prey.

The aim of the present study was to test the possible ameliorative efficacy of phytochemicals such as tannins on intestinal inflammation and dysbiosis. The effect of a chestnut shell (Castanea sativa) extract (CSE) rich in polyphenols, mainly represented by tannins, on k-carrageenan-induced intestinal inflammation in adult zebrafish (Danio rerio) was tested in a feeding trial. Intestinal inflammation was induced by 0.1% k-carrageenan added to the diet for 10 days. CSE was administered for 10 days after k-carrageenan induced inflammation. The intestinal morphology and histopathology, cytokine expression, and microbiota were analyzed. The k-carrageenan treatment led to gut lumen expansion, reduction of intestinal folds, and increase of the goblet cells number, accompanied by the upregulation of pro-inflammatory factors (TNFα, COX2) and alteration in the number and ratio of taxonomic groups of bacteria. CSE counteracted the inflammatory status enhancing the growth of health helpful bacteria (Enterobacteriaceae and Pseudomonas), decreasing the pro-inflammatory factors, and activating the anti-inflammatory cytokine IL-10. In conclusion, CSE acted as a prebiotic on zebrafish gut microbiota, sustaining the use of tannins as food additives to ameliorate the intestinal inflammation. Our results may be relevant for both aquaculture and medical clinic fields.

Aims The aim of the study was to investigate the skin microbiota of Prussian carp infested by ectoparasites from the genus Argulus and Lernaea. Methods and Results Associated microbiota of skin of Prussian carp and ectoparasites were investigated by sequencing of the V3, V4 hypervariable regions of 16S rRNA using Illumina MiSeq sequencing platform. Conclusions According to the Spearman rank correlation test, the increasing load of ulcerations of the skin of Prussian carp was weakly negative correlated with reduction in the abundance of the following taxa: Acrobacter, bacteria C39 (Rhodocyclaceae), Rheinheimera, Comamonadaceae, Helicobacteraceae, and Vogesella. In the present study, the microbiota of ectoparasites from genus Lernaea and Argulus were characterized for the first time. The microbiota associated with L. cyprinacea was significantly different from microbial communities of intact skin mucosa of both infested and uninfested fish and skin ulcers (ADONIS, p≤0.05). The microbiota associated with parasitic crustaceans L. cyprinacea were dominated by unclassified bacteria from Comamonadaceae, Aeromonadaceae families, and Vogesella. The dominant microbiota of A. foliaceus were represented by Flavobacterium, Corynebacterium, and unclassified Comamonadaceae. Significance and Impact of Study Results from these studies indicate that ectoparasites have the potential to alter skin microbiota, which can play a possible role in transmission of secondary bacterial infection in fish, caused by pathogenic bacteria.