Morphological changes in the gill of carp (Cyprinus carpio L.) exposed to acutely toxic concentrations of methyl bromide

The acute toxicity of methyl bromide (CH₃Br) to carp (Cyprinus carpio L.) was determined in experiments with a 4 h exposure period. The 4 h-LC₅₀ was calculated at approx. 17 mg 1⁻¹, i.e. the order of magnitude of actually encountered peak concentrations in surface water. The concentration-effect curve was found to be very steep and the response was somewhat delayed. Morphological damage to the gill epithelium, indicative of alkylation of cell membranes, was the most pronounced effect of CH₃Br. It consisted of initial swelling of the lymphatic space and vacuolization of the epithelial cells, followed by disintegration of the epithelium and invasion of leucocytes. Death of the fish was probably caused by suffocation.