Experiments were conducted to determine the effects of pH on ammonia and their combined effects on the stress response of steelhead trout, Oncorhynchus mykiss. Stress levels were studied by monitoring both primary and secondary stress responses. It was found that fish subjected to higher levels of pH and ammonia exhibited increased levels of stress. This was demonstrated through primary physiological stress response, plasma cortisol, and secondary physiological stress response, plasma glucose and blood hematocrit. It was concluded that careful regulation of pH and ammonia in the recirculating aquaculture system could relieve excessive stress allowing the fish for better survival and growth.

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