Cyanide detoxification in the mudskipper, Boleophthalmus boddaerti

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 LC50 for B. boddaerti were 0.37 mg HCN/liter, 0.34 mg HCNiliter, and 0.29 mg HCN/liter, respectively. The tolerance of B. boddaerti to cyanide does not involve a reduction of metabolic rate or a n enhanced anaerobic metabolism, or a cyanide-insensitive respiratory pathway. Instead, it is a result of the presence of a surplus of cytochrome oxidase and inducible cyanide-detoxifying 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 0 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 aminotransferase (CAT) and 3-mercaptopyruvate 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.Cyanide is a highly toxic compound. It binds to the heme of cytochrome c oxidase in place of molecular oxygen and causes the immediate, although reversible, inhibition of the electron transport chain in aerobic respiration. Preliminary experiments performed in the authors' laboratory revealed that the mudskipper, Boleophthalmus boddaerti, had a greater cyanide tolerance than other fishes. Mudskippers are goboid fishes that inhabit and build burrows on mudflats in estuaries. At low tide, B. boddaerti moves on the mudflats and enters the water occasionally. When the tide rises, it retreats into the hypoxic, if not anoxic, burrows (Gordon et al., '78) and remains submerged until the tide ebbs. The main objectives of these studies were therefore to establish the median lethal concentration (LC50) of cyanide for B. boddaerti and to examine if its high cyanide tolerance was related to its capacity to survive in the absence of O2 in its natural environment. The possibilities of the existence of c yanide-insensitive respiration and cyanide-detoxifying mechanisms in this fish were also examined. MATERIALS AND METHODS Collection and maintenance of B. boddaertiB. boddaerti (6-22 g body weight) were collected along the estuarine canal at Pasir Ris, Singapore. No attempt was made to separate the sexes. They were maintained in 50% seawater (SW; 15%0 salin-0 1992 WILEY-LISS, INC. ity) in small aquaria at 25°C. The aquaria were tilted slightly, so that the water covered only approximately half of the bottom surface of each tank. Water was changed daily and the fish were fed with Goldfish & Staple Flake@ (Everyday Co., Singapore) everyday.Determination of LCs0 o f cyanide for B. boddaerti Groups...

On the half-life of thiocyanate in the plasma of the marine fish Amphiprion ocellaris: implications for cyanide detection

“…Despite the differences in physiology, this elimination rate for SCN is within the range of that reported for SCN elimination in mammalian species upon exposure to CN (Logue et al, 2010). As previously mentioned, it is reasonable to expect marine fish to adhere to mammalian toxicokinetics pathways because the enzyme used to convert CN to SCN in mammals is also present in marine fish (Chew & Ip, 1992). Considering the accepted vertebrate detoxification pathway and the half-life of CN following an acute exposure, any attempt to measure CN concentration directly in marine fish must be carried out soon (hours) after the exposure.…”