The effect of calcium concentration on the toxicity of copper, lead and zinc to yolk-sac fry of brown trout, Salmo trutta L., in soft, acid water

Yolk-sac fry of brown trout were exposed to three levels of single trace metals (Cu, 20,40,80 nmol 1^-1; Pb, 12·5,25,50 nmol 1^-1; Zn, 75,150,300 nmol 1^-1) typical of concentrations reported for acid soft waters, in flowing, artificial, soft water media maintained at pH 4·5 and Ca] of 20 or 200 μmol 1^-1for 30 days.
Mortalities were high in fry subjected to all levels of the three trace metals at Ca] 20 μmol 1^-1, with 80% of the total deaths occurring between days 11 and 15 of the experiment. 25% mortality occurred at low Ca] and pH 4·5 in the absence of trace metals, with only one death recorded at Ca] 200 μmol1^-1'(Cu, 80 nmol 1^-1). At high Ca] all three levels of Cu and Pb impaired net Na and K uptake; Cu was the only metal to reduce the uptake of Ca. The Zn treatments had no significant effect on mineral uptake. Calcification of centra was reduced by all three Cu treatments at Ca] 200 μmol 1^-1. The lowest Zn concentration (75 nmol 1^-1) was the only other treatment to impair skeletal development. In the absence of trace metals, low Ca] significantly reduced Ca, Na and K uptake, skeletal calcification and dry mass at pH 4·5.
The deleterious effects of low Cu, Pb and Zn concentrations at low pH and low Ca], and the ameliorative effect of higher ambient Ca], are discussed in relation to fishery status in soft, acid waters.