Sexual Disruption in the Freshwater Crab (Geothelphusa dehaani).

To clarify the effect of environmental endocrine disruptors on the induction of secondary sexual characteristics in wild animals, we observed 1,527 male and 1,847 female specimens of sexually mature Japanese freshwater crabs, Geothelphusa dehaani, collected at 12 sample points from 10 rivers in Sasebo City, Nagasaki Prefecture, Japan. The results obtained were as follows: Abnormal males, with external appearance of a complete male, but having female genital openings, were observed at frequencies of 8-32% of males collected at all sample points. In contrast to this, all females collected were normal.