Kidney ATPase response in seawater-transferred rainbow trout (Oncorhynchus mykiss). Effect of salinity and fish size.

Abstract
Two sizes of domesticated rainbow trout (Oncorhynchus mykiss, 40 +/- 0.67 and 180 +/- 3.9 g) were directly transferred to brackish water (9 ppt) and seawater (28 ppt). Kidney Na(+)-K(+)-ATPase and Mg(2+)-ATPase activities were measured in fresh water, and after long-term seawater adaptation (up to 21 days). Renal Na(+)-K(+)-ATPase activity increased after saltwater loading in small trout, while large trout displayed an unmodified ATPase activity. The smallest trout showed a low but progressive increase in renal Mg(2+)-ATPase activity after the transfer to both salinities. However, ATPase activity remained unchanged or significantly decreased in large trout after the transfer to seawater or brackish water, respectively.
Keywords:
Body Weight, Seawater, Adaptation, Analysis of Variance, Animals, Ca(2 ) Mg(2 )-ATPase/chemistry, Kidney/enzymology/metabolism/physiology, Oncorhynchus mykiss, Physiological, Sodium Chloride/metabolism/pharmacology, Sodium-Potassium-Exchanging ATPase/chemistry
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