Ivermectin inhibits respiration in isolated rainbow trout (Oncorhynchus mykiss Walbaum) gill tissue

The effect of the anti-parasitic compound ivermectin on respiration of isolated rainbow trout gills was investigated. Control (saline only) gills had similar oxygen consumption rates to previous reports for perfused preparations. Ivermectin caused a significant, dose-dependent depression of gill oxygen consumption at concentrations of 1.21 mu g/ml and above, with an EC sub(50) of 2.15 mu g/ml. The carrier solvent (propylene glycol) exhibited dose-independent inhibition of branchial respiration by 12%. Assuming that these inhibitory effects were cumulative, ivermectin reduced gill respiration by up to 72% at a concentration of 11.2 mu g/ml. In comparison, excess (10 mM) ouabain resulted in a 40% drop in oxygen consumption. It is concluded that further characterisation of ivermectin's impact on fish health, and therefore welfare, is essential if its use for chemotherapeutic purposes in fish is to be licensed.