THE EFFECT OF MERCURY, COPPER AND CADMIUM DURING SINGLE AND COMBINED EXPOSURE ON OXYGEN CONSUMPTION OF ONCORHYNCHUSMYKISSWAL. ANDCYPRINUSCARPIO L. LARVAE

ABSTRACT. The oxygen consumption of common carp and rainbow trout larvae exposed to mercury, cadmium and copper was measured. The experiment was performed on seven-month-old common carp (0.9-1.39 g) and one-month-old rainbow trout larvae (1.2-1.5 g) reared under laboratory conditions. The fish were treated for one hour with solutions of a single metal or mixtures of Hg+Cd, Cd+Cu or Hg+Cu. The concentrations of single metals or mixtures were 0.025, 0.05, 0.1 and 0.2 mg l-1. Both single metals and mixtures reduced oxygen consumption in a concentration-dependent way. The results indicate that the oxygen consumption rate is a reliable indicator of metal toxicity to fish. The levels of oxygen consumption decrease indicate that the rankings of metal toxicity for the given nominal trace metal concentration are Hg+Cu> Cu> Cd+Cu> Cd+Hg> Cd for common carp and Hg+Cu> Cu> Cd+Hg> Hg for rainbow trout. The results show that copper is most toxic to both fish species. The mixtures are more toxic than single metals are and cause a greater reduction in oxygen consumption. Common carp larvae are apparently more sensitive to cadmium, while rainbow trout is more sensitive to mercury