Abstract:Salinity is an important environmental factor affecting the growth and metabolism of fish. The gill, kidney, and intestine are the main osmoregulatory organs involved in the adaptation of fish to changes in environmental salinity, and aquaporins (AQPs), the cystic fibrosis transmembrane regulator (CFTR), and the Na+/H+ exchanger (NHE) are important osmoregulatory genes in these organs. To study the osmoregulatory function of AQP1, AQP3, CFTR, and NHE1 in turbots (Scophthalmus maximus) under low salinity stress, their expressions in the gill, kidney, and intestine of turbots at salinity levels of 5 and 10 (5- and 10-salinity groups, respectively) were detected by quantitative real-time PCR. The results showed that the expression of AQP1 was very low in the gill but high in the kidney and intestine. Under low salinity stress, the expression of AQP1 in the gill did not change significantly in either of the salinity groups, but it increased significantly in the kidney and intestine (P<0.05). The expression of AQP3 was very low in the kidney, high in the gill, and low in the intestine. Under low salinity stress, the expression of AQP3 in the kidney did not change significantly in either of the salinity groups, but it increased significantly in the gill and intestine (P<0.05). Similarly, the expression of CFTR was very low in the kidney, high in the gill, and low in the intestine. Under low salinity stress, the expression of CFTR in the kidney did not change significantly in either of the salinity groups, but it decreased significantly in the gill and intestine (P<0.05). The expression of NHE1 was low in the gill and intestine but high in the kidney. Under low salinity stress, the expression of NHE1 in the gill did not change significantly in either of the salinity groups, but it increased significantly in the kidney and intestine (P<0.05). These results indicate that the expressions of the four genes vary according to tissue type, salinity, and time, thus reflecting their functional specificity. Under low salinity stress, these genes responded positively and their expressions changed to varying degrees, thus suggesting the roles of AQP1, AQP3, CFTR, and NHE1 in the adaptation of turbots to low salt environments. In addition, the results of this study can provide theoretical basis for brackish water aquaculture and desalination aquaculture of turbots as well as theoretical and technical support to improve the breeding of turbot varieties and their adaptation to low salinity environments.
