Toxicité d’un insecticide carbamate : Le néocide vis-à-vis des alevins de loup

Abstract

Neocide is a carbamate insecticide only weakly dissolved in sea water. Its related to the length of time the individual is tested in solution (the lethal concentration killing 50% of the fish in 24 hrs is different from that killing 50% of fish in 48 hrs). When sea-bass fry (D. labrax) are tested in solutions in average of Lc 50, a change in colour can be observed. This is caused by stress which paralyzes the animal. This phenomen can be reversible in water free from solution. Using mullet fry (M. labrosus) we have discovered a variation in levels of toxicity of the insecticide in relation to the number of frys and the volume of water in the aquarium. In fact for a given dose of neocide; when the volume of water is constant, the greater the amont of fry tested per aquarium (n), the greater the the descrease in the mortality rate; and when (n) is kept constant the greater the amont of water used, the greater is the increase in the percentage of the mortality. The length of exposure to the polluante remains constant (48 hr). Because the experiments have only been carried out using small quantities, one must be carefull when extending the effects of the product in open water.