Influence of cadmium concentration and length of exposure on metabolic rate and gill Na⁺/K⁺ ATPase activity of golden shiners (Notemigonus crysoleucas)

Although metabolic rate is considered to be useful as a general indicator of the biological effects of exposure to metals, it is seldom measured in conjunction with specific physiological, biochemical or cellular parameters. The purpose of this investigation was to examine the influence of cadmium (Cd) exposure on metabolic rate and gill Na⁺/K⁺ ATPase activity in golden shiners (Notemigonus crysoleucas). Shiners were exposed to six levels of Cd (ranging from control to the maximum sublethal concentration) for 24- and 96-h periods. After 24-h, metabolic rate and Na⁺/K⁺ ATPase activity of individual fish were strongly correlated. Shiners exposed to the four highest Cd concentrations (500, 800, 1100, and 1400 μg L ^{- 1}) for 24-h exhibited a shock response that was characterized by mean values for metabolic rate and Na⁺/K⁺ ATPase activity that were significantly lower compared to the control. Although results for 96-h exposures reflect a repair/recovery phase, there was no significant correlation between metabolic rate and Na⁺/K⁺ ATPase activity. Metabolic rate of shiners was significantly elevated (65-100%) at all concentrations compared to the control after 96-h, whereas Na⁺/K ⁺ ATPase activity did not differ from the control. Elevated metabolic rate after 96-h likely reflects the influence of a variety of energetically demanding processes associated with repair and recovery.