More male fish embryos near a pulp mill

Exposure to endocrine disrupters during early life stages may cause severe long-term effects. One process likely to be affected is sexual differentiation, which in fish can be influenced by both exogenous androgens and estrogens. To investigate if sexual differentiation is disturbed in wild fish exposed to pollutants, we studied embryonic sex ratios in a viviparous, gonochoristic fish species, the eelpout (Zoarces viviparus), whose embryos complete sexual differentiation before birth. The normal sex ratio of the eelpout was close to 50% females at four reference stations. In the effluent gradient of a large Swedish pulp mill, however, the sex ratios were significantly male biased. In light of the endocrine disturbances found near several pulp and paper mills in Europe and North America, it is suggested that endocrine disrupters may interfere with sexual differentiation and, thereby, affect the reproductive potential of fish populations.