Abstract
The tolerance of the mudskipper, Boleophthalmus boddaerti, to cyanide is higher than those of other fishes reported elsewhere. The 24 h, 48 h, and 96 h LC~50~ for B. boddaerti were 0.37 mg HCN/liter, 0.34 mg HCN/liter, and 0.29 mg HCN/liter, respectively. The tolerance of B. boddaerti to cyanide does not involve a reduction of metabolic rate or an enhanced anaerobic metabolism, or a cyanideโinsensitive respiratory pathway. Instead, it is a result of the presence of a surplus of cytochrome oxidase and inducible cyanideโdetoxifying mechanisms in this mudskipper. Although cytochrome oxidase activities in the various tissues of the fish exposed to 0.23 mg HCN/liter were inhibited by more than 50%, no reduction in the O~2~ consumption rate was observed. B. boddaerti could detoxify cyanide to thiocyanate. The activity of rhodanese in the liver extract of fish exposed to cyanide increased significantly compared to that of the control. The activities of cysteine aminoโtransferase (CAT) and 3โmercaptopyruvate sulfurtransferase (MPST) in the extracts from the liver and the muscle of B. boddaerti exposed to cyanide also increased significantly compared to those of the control fish. Glutamate formed in the reaction catalyzed by CAT could undergo transamination leading to the accumulation of aspartate in the muscle of the fish exposed to cyanide.