Correlation between biochemical parameters and susceptibility of freshwater fish to malathion.
Acute toxicity (96-h LC50) of malathion was tested using five species of freshwater fish, namely, topmouth gudgeon (Pseudorasbora parva), goldfish (Carassius auratus), nile tilapia (Tilapia nilotica), mosquitofish (Gambusia affinis), and rainbow trout (Salmo gairdneri). Correlation was found between susceptibility and biochemical parameters such as activity of brain acetylcholinesterase (AChE) and in vitro resistance of the enzyme to inhibition (IC50) of malaoxon (a major metabolite of malathion). The in vitro study also showed that malaoxon instead of malathion was the main inhibitor of AChE. Susceptibility to malathion was considerably changed as the fish was pretreated with piperonyl butoxide (PB, a P-450 inhibitor) and triphenyl phosphate (TPP, an inhibitor of carboxylesterase), respectively. Toxicity of malathion was significantly increased by TPP, but the responses of fish to PB were quite different among species. This suggested that both carboxylesterase and monooxygenase played an important role in susceptibility determination, and great variations existed among species in activity of monooxygenase.
Li Shao-Non
Department of Plant Protection, Zhejiang Agricultural University, Hangzhou, People's Republic of China.
Fan De-Fang
D000110:Acetylcholinesterase / Q000378:metabolism; D000818:Animals; D001921:Brain / Q000187:drug effects* / Q000201:enzymology; D043182:Carboxylesterase; D002265:Carboxylic Ester Hydrolases / Q000037:antagonists & inhibitors; D003530:Cyprinidae / Q000378:metabolism; D003532:Cyprinodontiformes / Q000378:metabolism; D065607:Cytochrome P-450 Enzyme Inhibitors; D005399:Fishes / Q000378:metabolism*; D005618:Fresh Water; D006054:Goldfish / Q000378:metabolism; D007306:Insecticides / Q000378:metabolism / Q000633:toxicity*; D007928:Lethal Dose 50; D008294:Malathion / Q000378:metabolism / Q000633:toxicity*; D017686:Oncorhynchus mykiss / Q000378:metabolism; D010755:Organophosphates / Q000633:toxicity; D010574:Pesticide Synergists / Q000633:toxicity; D010882:Piperonyl Butoxide / Q000633:toxicity; D013045:Species Specificity; D017210:Tilapia / Q000378:metabolism; D014874:Water Pollutants, Chemical / Q000378:metabolism / Q000633:toxicity*
D065607:Cytochrome P-450 Enzyme Inhibitors; D007306:Insecticides; D010755:Organophosphates; D010574:Pesticide Synergists; D014874:Water Pollutants, Chemical; D002265:Carboxylic Ester Hydrolases; D043182:Carboxylesterase; D000110:Acetylcholinesterase; D010882:Piperonyl Butoxide; D008294:Malathion; C005445:triphenyl phosphate