Accumulation of zinc by rainbow trout as influenced by pH, water hardness and fish size

Abstract

AbstractThe intrinsic toxicity of zinc within fish may be defined as the amount of zinc present in the gills (the site of acute toxicity) at death. This intrinsic toxicity was similar in rainbow trout (Salmo gairdneri Richardson) that were exposed to zinc in acid or neutral water (pH 5.5 or 7.0) and in hard or soft water (total hardness 390 or 30 mg CaCO3/L). Since much more zinc was needed in the water to cause death at low pH and at high hardness, these conditions must alter the uptake and/or excretion dynamics of zinc in gill tissue to produce a slower rate of zinc accumulation. Additional evidence supporting this conclusion is presented. A 17‐fold increase in fish size, from 1.7 to 29.0 g, reduced tolerance of zinc by a factor of 3.2, whereas a 14‐fold increase in fish size, from 1.3 to 18.2 g, reduced the median lethal time by a factor of 2.7. This reduced tolerance and resistance in larger fish appeared to result from increased intrinsic toxicity of zinc. All sizes of fish showed similar rates of zinc accumulation in the gills, of about 40 μg/g · h.