Toxicity of certain mosquito larvicides to the larvivorous fishes Aplocheilus lineatus (cuv. & val.) and Macropodus cupanus (cuv. & val.)

Abstract

Bioassay studies reveal the toxicity levels of mosquito larvicides commonly used in the Trivandrum area (Kerala State, South India) to the indigenous larvivorous fishes Aplocheilus lineatus and Macropodus cupanus. The resistance of both fishes decreases with increasing time of exposure to the larvicides. When the two species are compared, M. cupanus appears to be more resistant than A. lineatus, probably because of its obligate air-breathing nature, and thus its tendency to absorb less toxicant from the aquatic medium across the gills. Thus M. cupanus is more suitable than A. lineatus for introduction into areas liable to be polluted by mosquito larvicides. The utilisation of A. lineatus in wells, in conjunction with the larvicide temephos, for anti-larval work is cautioned against, since the spray dosage of temephos against anopheline larvae in wells in India is in excess of the 48-h LC50 value of A. lineatus.