Effect of Salinity on the Gut Microbiome of Pike Fry (Esox lucius)

The increasing popularity of pike in angling and fish farming has created a need to increase pike production. However, intensive pike farming is subject to limitations due to diseases and pathogens. Sodium chloride (NaCl) could be a good alternative to chemotherapeutics, especially for protecting the fish against pathogens and parasites at early life stages. However, the impact of high salinity on the symbiotic bacteria inhabiting freshwater fish is still unclear. Therefore, our objective was to analyze the gut microbiome to find possible changes caused by salinity. In this study, the influence of 3 parts per thousand and 7 parts per thousand salinity on pike fry was investigated. High-throughput 16S rRNA gene amplicon sequencing was used to profile the gut microbiome of the fish. It was found that salinity had a statistically significant influence on pike fry mortality. Mortality was highest in the 7 parts per thousand salinity group and lowest in the 3 parts per thousand group. Microbiological analysis indicated that Proteobacteria and Actinobacteria predominated in the pike gut microbiome in all examined groups, followed by lower percentages of Bacteroidetes and Firmicutes. There were no statistically significant differences in the percent abundance of bacterial taxa between the control group and groups with a higher salinity. Our results suggest that salinity influences the gut microbiome structure in pike fry, and that 3 parts per thousand salinity may be a good solution for culturing pike at this stage in their development.