Rainbow trout Salmo gairdneri were grown from November 17, 1979, to March 18, 1980, in static-water ponds in Alabama. Stocking densities of 55-g fish in the 0.04-hectare ponds ranged from 29,640 to 59,280 fish per hectare. Dissolved-oxygen concentrations were kept above 5.0 mg/liter with mechanical aerators, and fish production was limited by accumulation of unionized ammonia (NH3). Neither growth nor survival was significantly correlated with stocking density, but both were inversely related to the average daily maximum concentration of NH3(r = -0.62, P < 0.1 for growth; r = -0.75, P < 0.02 for survival). Because all mortality was caused by parasite epizootics, exposure to ammonia may have predisposed the fish to infection.
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Soderberg et al. (1983) studied this question.
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