Abstract: In the present study, the Japanese eels (505.1±35.7） g, Anguilla japonica, were reared at salinity 0 (control), 10, 33 for 14 days respectively. The serum osmolality, ion concentration and activity of gill Na⁺/K⁺-ATPase were measured at 0, 1, 4, 12, 24, 96 h and 14 d. The result showed that the isosmotic point was estimated as 329.1 mOsm·kg^-1 and corresponded to salinity 10.48. With the increased duration of experiment, serum osmolality and ions (Na⁺, Cl^-) concentration showed a similar fluctuating tendency of a decrease after an initial increase. The serum K⁺ concentration was less affected by the salinity. The gill Na⁺/K⁺-ATPase activity in salinity 10 reached the minimum (5.40±0.72） μmol·mg^-1·h^-1 at 12 h, and then recovered to （7.17±0.85） μmol·mg^-1·h^-1 at 96 h, which was not significantly different from that in the control (P>0.05). However, at salinity 33, the gill Na⁺/K⁺-ATPase activity descended acutely, then ascended rapidly and the maximum was observed at 24 h (13.05±0.62） μmol·mg^-1·h^-1, which was 1.5 times higher than that in the control (P<0.05). Therefore, there were three phases in the osmoregulation of Japanese eels in response to salinity change. The first was the ra〖HJ*3〗pid increase period, in which serum osmolality and ions (Na⁺, Cl^-) concentration increased abruptly, whereas the gill Na⁺/K⁺-ATPase activity was inhibited. The second was the slow increase period, in which serum osmolality and ions (Na⁺, Cl^-) increased slowly, and the gill Na⁺/K⁺-ATPase activity was activated to compensate the loss of water to alleviate the rise of osmolality. The third was the adaptation period, in which the gill Na⁺/K⁺-ATPase activity was in high state, and the active transport ability was enhanced, resulting in gradual recovering of the serum osmolality and ions (Na⁺, Cl^-) concentration.

Key words: ecosystem service bundles, Inner Mongolia Autonomous Region., ecological function zoning, SOFM neural network