Gut microbiota of healthy and saprolegniosis-affected whitefish (<i>Coregonus nasus</i>) producers in aquaculture

Background: The gut microbiota is one of the main factor influencing the immunity of animals, including fish. Understanding the taxonomic and quantitative composition of the microbiota may hold the key to enhance fish immunity against bacterial and fungal infections in aquaculture that potentially could optimize fish farm management. Aim: The aim of this work is to determine the taxonomic composition differences of the gut microbiome between healthy and Saprolegnia-affected breeders of broad whitefish (Coregonus nasus, Pallas, 1776) under industrial farming conditions using high-throughput sequencing. Methods: The gut microbiota composition was analyzed using NGS sequencing and the methods of bioinformatics. Hematological profiling was performed using standard microscopy-based techniques. Results: Preliminary data from high-throughput molecular genetic screening of the gut microbiota diversity in healthy and Saprolegnia-affected C. nasus individuals during the spawning period are presented. The hematological profile reliably distinguishes clinical differences between healthy fish and those infected with Saprolegnia. Differences in the taxonomic and quantitative composition of the gut microbiomes in C. nasus has been shown. Conclusion: Fish with the clinical signs of saprolegniosis showed a dominance of the phylum Proteobacteria (on average of 45.3%). There were comparable propotions (26.67–30.27%) of Proteobacteria, Firmicutes, and Actinobacteriota observed in healthy fish.