Plasma Cortisol Changes in Seawater-Adapted Mummichogs (Fundulus heteroclitus) Exposed to Ammonia

Abstract

Seawater-adapted mummichogs (Fundulus heteroclitus) were exposed to total NH4-N concentrations of 1, 2, 5, 10, 25, 50, 100, 150, and 200 mg/L for periods of 2, 4, 8, 12, 18, 24, 36, and 48 h. Afterward, the fish were captured quickly and anesthetized with MS-222 before blood was collected. The concentration of total NH4-N and duration of exposure accounted for, respectively, ~35 and <4% of the observed increase in plasma cortisol. The effective concentration (the concentration of total NH4-N inducing a mean cortisol response two standard deviations above the mean of the controls) was 47.14 mg/L, corresponding with a mean cortisol level of 13.44 μg/dL. Test concentrations of NH3-N were calculated from total NH4-N, pH, salinity, and temperature (constant at 20 °C), and the effects of both forms of ammonia on plasma cortisol concentration were compared. Significance was not detected at p < 0.05, demonstrating that total NH4-N and NH3-N explained the observed changes in cortisol levels similarly. Mean cortisol concentrations of mummichogs anesthetized and sampled in the field were comparable with published values and did not differ significantly from the mean value of captive control fish sampled after the same length of time in MS-222 (p < 0.05).