Effects of water pH on copper toxicity to early life stages of the common carp (Cyprinus carpio)

Carp eggs were exposed immediately after fertilization to Cu concentrations of 0.3 and 0.8 μmol/L at water pH 7.6 or pH 6.3. Mortality, the incidence of spinal cord deformation, heart rate, tail movements, hatching success, and whole-body content of K, Na, Mg, Ca, and Cu were determined over time. Light microscopical preparations of eggs (48 h after fertilization) and larvae (168 h after fertilization) were studied. At pH 7.6, Cu did not affect egg mortality, heart rate, tail movements, and whole-body K and Mg content. Hatching success increased only in the 0.3 μmol/L Cu group. Exposure to 0.8 μmol/L Cu increased larval mortality and larval deformation and decreased whole-body Na and Ca content. At pH 6.3, exposure to 0.8 μmol/L Cu increased egg mortality and decreased heart rate and tail movements. Furthermore, premature hatching, a concentration-dependent increase of larval mortality, and larval deformation was observed. Exposure to 0.3 and 0.8 μmol/L Cu decreased the whole-body content of K, Na, Mg, and Ca. Uptake of Cu after hatching increased two-fold at pH 6.3 compared to the pH 7.6 groups. At pH 6.3, all Cu-exposed larvae were unable to fill their swim bladder. Also, after 168 h the yolk sac remained largely unabsorbed in the 0.3 and 0.8 μmol/L Cu group. Exposure to 0.8 μmol/L Cu resulted in coagulation of proteins in eggs and yolk sacs. No significant changes in any of the assessed parameters were observed in control groups of pH 6.3 and pH 7.6.