70.4 Saturday, Jan. 5 Osmoregulatory disruption due to acute cold stress in a juvenile estuarine fish ANDERSON, D.A.*; SOUTHWOOD WILLIARD, A.; SCHARF, F.S.; University of North Carolina Wilmington; University of North Carolina Wilmington; University of North Carolina Wilmington email@example.com
Marine fishes rely on active transport of ions to maintain osmotic homeostasis. Impaired function of critical ion pumps, such as Na+/K+ ATPase, at extremely low temperatures may result in a disruption in osmotic and ionic balance that could ultimately lead to death. We tested the temperature sensitivity of Na+/K+ ATPase in red drum (Sciaenops ocellatus), a dominant sport fish that encounters extreme cold temperatures during the first winter of life at the northern extent of its range. In a controlled laboratory setting, juvenile red drum were exposed to water temperature treatments of 1, 3, and 5°C, which represented within-range minima, with a 10°C control treatment. Tissue was then collected from cold-stressed and control fish for analysis of enzyme function, water content, and internal ion concentration. We used kinetic assays to compare Na+/K+ ATPase activity in gill tissue with and without ouabain, a Na+/K+ ATPase inhibitor, for each treatment group. Assays were run at both 15 and 25°C to identify enzyme temperature sensitivity within treatments. Results indicate that enzyme activity is positively correlated to the severity of thermal stress (i.e., highest activity at the coldest treatment temperature), and activity increased at the higher assay temperature within each treatment group. In order to complement our assessment of thermal effects on ion transport, we measured water content of muscle tissue and ion concentration of muscle tissue via atomic absorption spectroscopy. Measuring the effects of acute cold stress on osmoregulatory function offers insight to seasonal shifts in physiology and causes of mortality for juvenile red drum.