The effects of a synthetic pyrethroid pesticide on some aspects of reproduction in Atlantic salmon (Salmo salar L.).

The synthetic pyrethroid pesticide cypermethrin, a known contaminant of tributaries supporting spawning salmonid fish, had a significant sublethal impact upon the pheromonal mediated endocrine system in mature male Atlantic salmon (Salmo salar L.) parr. Previous studies have demonstrated that ovulated female salmon release a priming pheromone in their urine (considered to be the F-type prostaglandin, PGF(2alpha) which is subsequently detected by the olfactory system of mature male salmon parr and results in increased levels of plasma sex steroids and expressible milt. Exposure of mature male parr for a 5 day period to a water concentration of < 0.004 microg l(-1) cypermethrin significantly reduced or inhibited the olfactory response to PGF(2alpha). In addition, exposure of male parr to cypermethrin significantly reduced their ability to respond to the priming effect of the pheromone. The priming effect on milt and plasma 17,20beta-dihydroxy-4-pregnen-3-one levels were abolished at water concentrations of < 0.004 and 0.028 microg l(-1)cypermethrin, respectively. The effect of cypermethrin on the priming response did not appear to be due to a direct effect on the testes, since the ability of testes to respond to pituitary extract stimulation in vitro was not impaired in males exposed to cypermethrin. In addition, exposure of salmon milt and eggs to a concentration of 0.1 microg l(-1) cypermethrin during fertilisation subsequently reduced the number of fertilised eggs. The results of the study suggest that low levels of cypermethrin in the aquatic environment may have a significant effect on Atlantic salmon populations through disruption of reproductive functions.