Plasma Corticosteroid Dynamics in Channel Catfish (Ictalurus punctatus) Exposed to Ammonia and Nitrite

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Abstract
Plasma corticosteroid concentrations in channel catfish (I. punctatus) increased in response to increasing concentrations of both NH3 and NO2. Corticosteroid levels in fish exposed to NO2 increased continuously during a 24-h exposure; corticosteroid concentrations of fish exposed to NH3 peaked after 8 h and then decreased for the remainder of the 24-h experiment. Low environmental pH and elevated environmental chloride were effective in preventing elevated corticosteroid levels in fish exposed to NH3 and NO2, respectively. Based on plasma corticosteroid concentrations, no additive or synergistic toxic interaction was evident in fish simultaneously exposed to environmental NH3 and NO2. Corticosteroids are released into circulation probably in response to a physiological dysfunction brought about by the toxins and not simply their presence in the environment. The absence of a toxic interaction between NH3 and NO2 as measured by plasma corticosteroid concentrations may be due to the temporal separation of their toxic effects coupled with the apparently rapid ability of channel catfish to acclimate to NH3.

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