Scientists have recently discovered that fish in the Northeastern U.S. are changing gender – and it has nothing to do with the keen hand of any surgeon. A groundbreaking study in the journal Ecotoxicology and Environmental Safety has found that male fish are turning into females. The phenomenon, known as intersex, is when a creature is born with a reproductive or sexual anatomy that doesn’t seem to fit the typical definitions of male or female. 

It is believed that this is due to chemical pollution, specifically estrogenic endocrine disrupting chemicals (EEDCs), man-made chemicals that alter the way the body functions and cause various health defects by interfering with the synthesis, metabolism, binding or cellular responses of natural estrogens. The researchers found that around 85 percent of smallmouth bass (Micropterus dolomieu) and around 27 percent of largemouth bass (Micropterus salmoides) from 19 National Wildlife Refuges from Maine to Virginia, showed signs of intersex.

The concern now is whether more than just fish have been affected, as there is a large diversity of species that frequently visit the refuges. If it can effect fish, who’s to say that these effects cannot spread to other wildlife?

Where EEDCs come from

EEDCs can be found in chemicals in soy plants and soy-derived products to synthetic pharmaceuticals such as some birth control pills, certain plastic products, natural sex hormones in livestock manures, and pesticides and herbicides. Extreme concentrations of estrogen – the primary female sex hormone – is capable of hindering the natural hormone system of fish, topside wildlife and even humans. It can cause reduced sperm count and viability, reproductive failure, and population decline.

It was found that EEDCs were present in all types of water bodies sampled – rivers, reservoirs, lakes and ponds. Now researchers are focusing on how to stop these chemicals entering the water, and how to mitigate harm to the resident wildlife.

Department of Biology (2016), Estrogen-like endocrine disrupting chemicals affecting puberty in humans–a review, 
Christina Selby (2016), A sex change phenomenon in fish,