Physiological Response of Juvenile Rainbow Trout,Salmo gairdneri, to Acid and Aluminum — Prediction of Field Responses from Laboratory Data

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Abstract
An initial 1 to 2-h exposure of juvenile rainbow trout (Salmo gairdneri) to 2.8 .mu.M (= .mu.mol .cntdot. L-1) inorganic aluminium caused increased ventilation and activity responses ranging from slight to severe depending on the ambient pH. The severity of physiological response after 6-11 d of exposure was similar to that of the initial response. This was severe at pH 6.1, 4.5, and 4.0, slight to moderate at pH 5.0 and 5.5, but minimal at pH 6.5. In the severe response groups, 40-90% of the fish died after a few days of exposure. Death was due primarily to hypoxia at pH 6.1 and to electrolyte loss at pH 4.5 and 4.0. Between pH 5.5 and 5.0 there was a transition between the two mechanisms. With 8-10 mg natural organic acids .cntdot. L-1 the response to the same concentration of inorganic aluminum was unchanged at pH 5.0 but was slightly increased at pH 4.5. Fish kills of salmonids that have occurred in South Norway could have been predicted from these results. In North America the presence of refuge areas and the prevalence of more tolerant species could account for the occurrence of sublethal rather than lethal responses.