Osmoregulatory Parameters of Asian sea bass (Lates calcarifer) during adaptation in Freshwater

In the present study, the adaptation of Asian sea bass (lates calcarifer) was investigated in fresh water using physiological parameters of osmoregulation including: the plasma levels of thyroid hormones and cortisol, gill Na+/ K+-ATPase activity and plasma concentrations of sodium and chloride. For this purpose, 60 fish were distributed in three 300 L tanks with a density of 20 fish per tank. Fish sampling was done in two steps: Step 1) Before adaptation in freshwater (sea water stage) and step 2) After 24 hours adaptation in fresh water. According to the results, the activity of Na+/ K+-ATPase significantly increased during the period of adaptation in fresh water (p<0.05). Thyroid hormones showed a significant increase during 24 adaptation in fresh water (p<0.05). Also, cortisol levels did not change during the adaptation period (p>0.05). The concentration of sodium and chlorine ions significantly decreased during the adaptation period in fresh water (p<0.05). Additionally, 10% mortality was observed during the period of adaptation. The results of this study showed that Asian sea bass can be adapted to freshwater shock. However, it seems that the proper ion balance obtains at adaptation period more than 24 h.