Experimental investigations on the toxicity of ammonia: effects on ventilation frequency, growth, epidermal mucous cells, and gill structure of rainbow trout Salmo gairdneri

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Abstract
Juvenile rainbow trout Salmo gairdneri Rich. were experimentally exposed to 0.25 mg 1-1 of NH3 for 4 wk. This concentration lies between those causing acutely lethal and sublethal effects. At first, significant effects from the ammonia were recorded; greatly increased ventilation frequency, reduced food intake and an associated decrease in weight gain. Subsequently, the fish adapted considerably to the toxicant. Ventilation frequency decreased, although it remained above that of controls. Food was taken up completely and there was only a minor difference in growth between exposed trout and unexposed controls. No change from exposure to the pollutant could be detected in the number of mucous cells in the epidermis. Examination of the gill structure at the end of the experiment revealed only a slight, but significant, tissue proliferation. Unexpectedly, the comparatively high ammonia concentration produced few chronic effects. Nevertheless, results indicate that the well-being of the experimental fish was disturbed.

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