Researchers, including physiological ecologist Chris Murray, are trying to figure out what is changing the sex of crocodiles in Costa Rica. They found that the population is becoming skewed towards males, with an assessment finding that male hatchlings were outnumbering females three or four to one, depending on the study.
It was suspected that a hormone, 17α-methyltestosterone (MT), could be to blame for this change. The investigators began to speculate on where could it be coming from since the primary users of the drug are older breast cancer patients or men with a testosterone deficiency. It seems that fish farms raising tilapia nearby are using it; the drug makes more male than female tilapia, generating higher profits for the fish farms.
After the researchers tested the drug in the laboratory, they found that "MT does have a masculinizing effect" on crocodilians, said Murray. The source remains a question, however. Ecologist Frank Chapman noted that if it is the farms, it is a reversible effect. Check out the video to learn more.