Evaluate salinity stress in Mystus gulio to explore potential farming in brackish water

This study aims to assess the effects of salinity on the growth and survival of freshwater catfish Mystus gulio and to analyse the biochemical and hormonal alterations. The fish were exposed to increasing salt concentrations of upto 22.27 PSU in experimental tanks within a study period of 21 days with an aim to investigate into the effect of salinity stress on the total protein profile and, synthesis of the stress hormone cortisol and stress protein HSP70 as well as the sex steroid hormones estradiol and testosterone. This euryhaline fish showed tolerance with different salinities upto approximately 9 PSU beyond which, most fishes succumbed to higher salinities. 50% of mortality was noticed at salt concentrations between 8.14-8.19 PSU. There was a gradual decrease in the protein concentration with increasing salt concentrations. SDS-PAGE revealed the disappearance of a 91.5 kDa, 77.8 kDa and an 18.2 kDa protein band and the appearance of a 60.7 kDa, 21.4 kDa and a 15.5 kDa protein band at higher salt concentrations. The Cortisol and HSP70 concentration showed a gradual increase in muscle tissue with increasing salinities but in case of gills there was a gradual decline after an initial sharp rise. Low salinity stress upregulated estradiol synthesis but level of testosterone showed a decrease with increasing salt concentrations.