Abstract
Keywords: H.sup.+ excretion; H.sup.+-ATPase; Osmoregulation; Metabolic acidosis; Hypersaline water Increases in ambient salinity demand parallel increases in intestinal base secretion for maintenance of osmoregulatory status, which is likely the cause of a transient acidosis following transfer of euryhaline fish from freshwater to seawater. It was predicted that transfer of the marine Gulf toadfish (Opsanus beta) from seawater (35 ppt) to hypersaline (60 ppt) seawater (HSW) would lead to a transient acidosis that would be compensated by increases in branchial acid excretion to offset the acid--base disturbance. Toadfish exposed to HSW showed a significant decrease in blood pH and [HCO.sub.3.sup.-] but no increase in pCO.sub.2, followed by a full recovery after 48--96 h. A similar metabolic acidosis and recovery was found when fish were exposed to 60-ppt HCO.sub.3.sup.--free seawater (HEPES-buffered), which may suggest that compensation for intestinal base loss during hypersaline treatment is from gill H.sup.+ excretion rather than gill HCO.sub.3.sup.- uptake. However, we cannot rule out that reduced branchial HCO.sub.3.sup.- excretion contributed to an increase in net acid excretion. Since colchicine prevents full compensation, translocation of H.sup.+ and/or HCO.sub.3.sup.- transporters between cytosolic compartments and plasma membrane fractions might be involved in compensating for the hypersalinity-induced acidosis. Translocation of transporters rather than de novo synthesis may represent a faster and less energetically demanding response to rapidly fluctuating and high salinities encountered by toadfish in their natural environment. Author Affiliation: (1) Sino-US joint laboratory of Aquatic Animal Physiology, East China Sea Fisheries Research Institute, Chinese Academy of Fisheries Sciences, Shanghai, China (2) Department of Marine Biology and Ecology, Rosenstiel School of Marine and Atmospheric Science, University of Miami, Miami, FL, USA (3) Department of Biological Sciences, University of North Texas, Denton, TX, USA (4) Cardiovascular Sciences, School of Medical Sciences, The University of Manchester, Manchester, UK (a) yaozl@ecsf.ac.cn Article History: Registration Date: 09/30/2020 Received Date: 02/10/2020 Accepted Date: 09/29/2020 Online Date: 10/17/2020 Byline: