Infection and antibiotic treatment have prolonged effect on gut microbiota, muscle and hepatic fatty acids in rainbow trout (Oncorhynchus mykiss)

AIMS

The aim of the present study was to investigate the gastrointestinal (GI) microbiota and bacterium-specific fatty acid occurrence in the muscle and hepatic lipids of rainbow trout Oncorhynchus mykiss (Walbaum, 1792), both healthy and those naturally infected with bacterial pathogens.

METHODS AND RESULTS

From June 2017 (L1) to September 2018 (L8), 74 specimens of rainbow trout Oncorhynchus mykiss (with the average weight from 139.2 ± 7.1 g (L1) to 2191.7 ± 85.1 g (L8)) were studied. Amplicon sequencing targeted to the V3-V4 region of 16S rRNA gene fragments is used for identification of taxonomic composition of gut bacterial communities. Firmicutes, Bacteroidetes, Proteobacteria, Tenericutes, and Fusobacteria were the major phyla. Besides behavioural and physiological manifestations of the bacterial mixed disease (yersiniosis, pseudomonosis, and flavobacteriosis), some disorders induced both the infection and followed antibiotic treatment were detected in the host organism, including (1) a progressive decrease in the content of odd-chain saturated fatty acids of bacterial origin within the trout lipid molecules and (2) abnormalities in trout GI tract microbiota, such as the elimination of LAB and progressive occurrence of certain bacterial taxa, particularly Mycoplasmataceae.

CONCLUSIONS

The GI bacterial flora varied principally due to Mycoplasmataceae and Lactobacillaceae, which could be considered in the search for bioindicators. The content of specific bacterium-derived fatty acids incorporated into the lipids of trout muscle and hepatic seems to be related to the prevalence of bacterial taxa, and their deficit could be regarded as an early warning sign of microbiota disturbance.

SIGNIFICANCE AND IMPACT OF STUDY

Our results demonstrated that infectious disease and antibiotic treatment of reared species can cause pertinent imbalance in their gut microbiota and reduce the abundance of specific fatty acids. This can be useful for the sustainable aquaculture industry due to development of early indication technologies for rapid disease diagnosis.

Variations of the intestinal gut microbiota of farmed rainbow trout, Oncorhynchus mykiss (Walbaum), depending on the infection status of the fish

AIMS

The aim of the present study was to investigate the composition of the intestinal microbiota during the acute stage of a bacterial infection to understand how dysbiosis of the gut may influence overall taxonomic hierarchy and diversity, and determine if there exists a bacterial taxon(s) that serve as markers for healthy or diseased rainbow trout (Oncorhynchus mykiss).

METHODS AND RESULTS

From July to September 2015, 29 specimens of 3-year-old (an average weight from 240·9 ± 37·7 to 850·7 ± 70·1 g) rainbow trout O. mykiss were studied. Next-generation high-throughput sequencing of the 16S ribosomal RNA genes was applied to stomach and intestinal samples to compare the impact of infection status on the microbiota of rainbow trout O. mykiss (Walbaum) from the northwest part of Eurasia (Karelian region, Russia). The alpha diversity (Chao1, Simpson and Shannon index) of the microbial community of healthy rainbow trout was significantly higher than in unhealthy fish. The greatest contribution to the gut microbial composition of healthy fish was made by OTU's belonging to Bacillus, Serratia, Pseudomonas, Cetobacterium and Lactobacillus. Microbiota of unhealthy fish in most cases was represented by the genera Serratia, Bacillus and Pseudomonas. In microbiota of unhealthy fish there were also registered unique taxa such as bacteria from the family Mycoplasmataceae and Renibacterium. Analysis of similarities test revealed the significant dissimilarity between the microbiota of stomach and intestine (P ≤ 0·05).

CONCLUSIONS

A substantial finding was the absence of differences between microbial communities of the stomach and intestine in the unhealthy groups if compared with healthy fish.

SIGNIFICANCE AND IMPACT OF THE STUDY

These results demonstrated alterations of the gut microbiota of farmed rainbow trout, O. mykiss during co-infections and can be useful for the development of new strategies for disease control programs.

Morphology and phylogeny of Henneguya oviperda infecting oocytes of Esox lucius, with description of parasite-induced histopathology

Henneguya oviperda (Cohn, 1895) (Myxozoa: Myxobolidae) is a parasite infecting oocytes of the northern pike Esox lucius Linnaeus, 1758 (Actinopterygii: Esocidae). Infected oocytes are surrounded by all oocyte layers, some of them thinner and less visible than intact oocytes. A mature plasmodium of H. oviperda fills the entire internal space of the oocytes at the secondary growth phase, rendering the nucleus and organelles of the latter undetectable. Apart from the observed degradation of internal structures, alterations in the envelopes of the infected oocytes, and the deformation of the intact oocytes adjacent to them, no other developmental anomalies have been found in the reproductive products of female northern pike. Mature spores of H. oviperda have oval bodies with polar capsules of almost equal size and caudal projections that are on average equal to the spore body length. Phylogenetic analysis comparing 18S rDNA sequences placed H. oviperda into a clade of esocid-infecting species of the genus Henneguya and also supported H. psorospermica as a sister species.