Short-term exposure to 5 parts per thousand and 15 parts per thousand salinity causes the dynamic changes of the NKA gene, enzyme activities and morphological characteristics in fish tissues of Gymnocypris przewalskii

Salinity affects the physiological activities of aquatic animals and determines the distribution of fish. In this study, we found that the naked carp survived under 0-15 parts per thousand salinity, but survival rates decreased to varying degrees under 20 parts per thousand and 25 parts per thousand salinity, which indicates that the safety threshold of salinity tolerance of Gymnocypris przewalskii is 0-15 parts per thousand. Next, the response rate of NKA alpha 1 in the gills and kidneys was significantly faster than in the livers, and the response intensity of NKA alpha 1 and NKA alpha 3 has certain tissue specificity under different salinity. NKA enzyme activity first increased, then gradually decreased and increased again in the gills and kidneys after 5 parts per thousand and 15 parts per thousand salinity stress. In contrast, the NKA enzyme activity gradually decreased and then gradually increased in the liver. Salinity stress also could lead to some pathological phenomena in the cytoplasm. These results indicated that changes in salinity can lead to differential expression of the NKA genes and enzyme in tissues. Also, the dynamic changes of the NKA gene, enzyme activities, and morphological characteristics in fish tissues are in response to the salinity changes in the living environment, thus maintaining a dynamic balance of ions inside and outside the cells.