Effects of Na+/K+ ratio of groundwaters on the gill ion-transport enzyme activity, plasma osmolality and growth of Cynoglossus semilaevis juveniles |
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| Authors: | Huizan Yang Luqing Pan Fawen Hu Hongyu Liu |
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| Institution: | (1) The Key Laboratory of Mariculture, Ministry of Education, Ocean University of China, Qingdao, 266003, P. R. China |
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| Abstract: | The effects of environmental Na+/K+ ratio on the gill ion-transport enzyme activity, plasma osmolality and growth of Cynoglossus semilaevis juveniles were investigated. The results showed that, plasma osmolality was similar among flounder adapted to different Na+/K+ ratios of saline groundwaters (P>0.05), while the growth, gill Na+, K+-ATPase and HCO3
−-ATPase activities were affected by Na+/K+ ratio significantly (P<0.05). The gill Na+, K+-ATPase activity reached its maximum on day 3, then decreased gradually from day 3 to day 9 and remained constant from day
9 to day 15. The peak values of gill Na+, K+-ATPase activity were detected on day 3 for all Na+/K+ ratios of saline groundwaters, then the enzyme activities descended, and on day 9 the enzyme activities achieved steady state,
and the gill HCO3
−-ATPase activity increased rapidly and achieved steady state after one day. During steady state, the gill Na+, K+-ATPase and HCO3
−-ATPase activity of Na+/K+ ratios 20 and 40 treatments were significantly higher than those in the control group (Na+/K+ ratio 27.5), while there were no significant differences between the Na+/K+ ratio 30 treatment and the control group; the gill Na+, K+-ATPase activity of Na+/K+ ratio 20 and 40 treatments were significantly higher than that for ratio 30 treatment, but there were no significant differences
of gill HCO3
−-ATPase activity among these treatments. At the end of the 15-day experiment, the weight gain (%) and specific growth rate
(SGR) of flounders maintained in seawater were significantly higher than those in groundwaters; significant differences also
occurred among the treatments; Na+/K+ ratio 30 treatment had the highest values (33.7% and 1.94 respectively), which were significantly higher than those under
Na+/K+ ratios 20 and 40 treatments. Therefore, for the saline groundwater used in this experiment, it is suggested that the Na+/K+ ratio be adjusted to approximately 30, i.e., as close to that of natural seawater as possible in the culture of flounder. |
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| Keywords: | Na+/K+ ratio Cynoglossus semilaevi ion-transport enzyme activity plasma osmolality growth |
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