Some effects of low pH and calcium on the growth and tissue mineral content of yearling brown trout, Salmo trutta

Yearling brown trout, Salmo trutta , were exposed to low mineral content water (nominal concentrations of 20μmol 1 −1 magnesium, 7.7 μmol 1 −1 potassium, 44 μmol 1 −1 sodium) over a pH range of 4.0–5.2 with ambient calcium concentrations of 2.5–60 μmol 1 −1 . All fish died at pH 4.0 and 4.2 irrespective of ambient calcium concentration and also at pH 4.4 with only 2–3 μmol 1 −1 calcium (that is calcium‐free water except for that leached from the diet or excreted by the fish). Good growth rates were obtained over the remaining treatments which extended down to pH 4.4 with as little as 7 μmol 1 −1 calcium. When starved, weight loss was inversely correlated with pH. Effects on plasma chloride, percentage dry weight and calcium, potassium sodium, and phosphorus contents of skin, muscle and bone tissue were also investigated. These demonstrated pH effects on mineral metabolism in starved fish, but no effects were detected in fed fish.