AbstractAsian sea bass, Lates calcarifer is one of the most valuable marine fish species that is known to be tolerant to wide range changes of salinity. The species is able to live in freshwater, brackish and marine water, being an ideal model species for studying the effects of salinity on physiological responses. The present study is aimed to evaluate the changes in expression levels of Na+-K+ATPase (NKA) and Na+/K+/2Cl–(NKCC) genesin gill tissue of L. calcariferkept in a range of salinities including freshwater (0 ppt), brackish water (15 ppt) and saline marine water (35 and 50 ppt). Totals of 180 individuals were randomly distributed into 12 fiberglass tanks (volume 300 L) that contained different water salinity variants. After 30 days of experimental captivity, fish were euthanized and gill tissues were collected for NKAand NKCCmRNAs expression analysis. The U shape expression pattern for both NKAand NKCCwas recorded. The highest brachial expression was seen in 50 ppt that was statistically different from all other salinity variants. The lowest expression was recorded in 35 ppt. In turns, observed NKAand NKCCexpression levels in freshwater were significantly higher than 15 and 35ppt. The current findings showed that the expression levels of major gill transporters, as are NKAand NKCChas the highest expression in unusual conditions, having the lowest expression levels under the most habitual salinity conditions present in the wild environment.IntroductionNowadays, the increasing world’s human census and changing dietary preferences cause the enlarged demand for aquatic products. As the classic fishery based on the wild-catches has reached its limit the aquaculture is expected to satisfy this demand in the future. Aquaculture is also considered as one of the most economically important branch of agriculture, continuously growing since 1990 and presently exceeding wild-catches (FAO, 2020). On the other hand, survival of many freshwater and marine species in endang