Pesticides proven to reduce fish libidos

Researchers at Aarhus University in Denmark have documented for the first time the effects on animal reproduction of even small doses of antiandrogenic pesticides and their residues. Antiandrogens are chemical compounds that block the normal function of male hormones, writes Michael de Laine.

The researchers used the small viviparous guppy as their model organism. The fish were given fish food to which the researchers had added small quantities of vinclozolin (a fungicide) and DDE (a decomposition product of the pesticide DDT). The amounts given were believed to equal those that the fish would get in nature.

Erik Baatrup and his team of researchers from Aarhus University's department of zoology were surprised to discover that the antiandrogenic power of the pesticides was as strong as or stronger than flutamid. Flutamid was specifically developed as an antiandrogen and belongs to the group of demasculinising medicaments used, for instance, to combat beard growth in women and in the treatment of rapists.

The effects of the pesticides on the fish were measured at several levels along the biological hierarchy from cell to population. Adult fish, new-born fish and fish foetuses were all exposed to the pesticides in the test, and even the smallest doses of the pesticides had measurable effects.

"In all cases, the male guppies in the experiments were more or less damaged in their male characteristics - they had fewer sperm cells, smaller testicles, smaller gonopodia (penises), their orange-yellow sexually attractive coloration shrank and faded and their sexual urge was markedly reduced," says Baatrup.

"The greatest damage was found in the fish that were affected in their early life stages, especially as foetuses. After sexual maturation, these fish gave birth to far fewer young than the control group," he adds.

"But the most astounding discovery is that the apparent antiandrogenous effects of these pesticides are as strong as in the fish in a control sample."