Osmoregulation and excretory nitrogen metabolism in the euryhaline four-eyed sleeper, bostrychus sinensis, exposed to salinity and ammonia stresses

Abstract

This study examines the effects of seawater and ammonia stress on nitrogen metabolism and osmoregulatory acclimation of euryhaline four-eyed sleeper, <i>Bostrychus sinensis</i>. <i>B. sinensis</i>, a facultative air-breather, exhibited hypoosmotic hypoionic osmoregulation in seawater. A novel finding here is that Na⁺/K⁺/Cl^- cotransporter, and not Na⁺/K⁺-ATPase, was up-regulated in the gills of <i>B. sinensis</i> after long-term acclimation to seawater. On the other hand, Na⁺/K⁺-ATPase was up-regulated in the intestine. Exposure to ammonia in 5 parts per thousand water or seawater led to significant increases in glutamine contents and glutamine synthetase in various tissues of fish. In addition, exposure to 15 mmol l^-1 NH₄Cl in seawater for 6 days resulted in a significant increase in the amination activity of glutamate dehydrogenase (GDH) from the intestine and a significant increase in the affinity of the GDH from the liver to NH₄⁺. Subsequently, two isoforms of GDH were identified and sequenced from <i>B. sinensis</i>.