Nitrogen metabolism and branchial osmoregulatory acclimation in the juvenile marble goby, Oxyeleotris marmorata, exposed to seawater.

The marble goby, Oxyeleotris marmorata, considered a freshwater fish, was able to hypoosmoregulate successfully during 14 days of acclimation to seawater (30 per thousand) following 6 days of progressive increase in salinity. In seawater, there were slight perturbations in plasma osmolality and ionic concentrations, and significant increases in contents of some free amino acids, which presumably acted as osmolytes, in tissues. The muscle glutamine content increased significantly during seawater acclimation, and the activity and the protein abundance of glutamine synthetase increased significantly in the liver of fish exposed to seawater for 14 days. Exposure to seawater for 14 days also resulted in branchial osmoregulatory acclimation. There were significant increases in the activity and the protein abundance of gill Na(+)/K(+)-ATPase, and protein abundance of gill Na(+):K(+):2Cl(-) cotransporter (NKCC). Immunofluorescence microscopy of branchial Na(+)/K(+)-ATPase-immunoreactive cells revealed that exposure to seawater led to increases in protein expression of apical cystic fibrosis transmembrane receptor-like chloride channel and basolateral NKCC. Overall, our results indicate that juvenile marble goby can acclimate to brackish water and subsequently to seawater, and prompt future studies on the effects of salinity on its growth and development which may have important application to the Asian marble goby aquaculture industry.