A common growth-promoting hormone used worldwide in the cattle industry has been found to affect the sexual behaviors of fish at a very low concentration in waterways -- with potentially serious ecological and evolutionary consequences. Researchers from Monash University, Australia in collaboration with researchers from Åbo Akademi University in Finland, have found that the steroid 17β-trenbolone -- used on livestock to increase muscle growth -- alters male reproductive behavior in guppy fish (Poecilia reticulata).

This androgenic growth promoter is part of a group of contaminants called endocrine disrupting chemicals (EDCs) that enter the environment through a variety of sources -- from discharge of household waste to agricultural run-off and industrial effluent.

Using trenbolone in livestock farming has been banned in the EU. However, in Denmark, researchers have measured high concentrations of it in gym sewage. Trenbolone is popular among bodybuilders. Trenbolone is used for example in the United States, Argentina and Australia.

One of the leading authors Dr Minna Saaristo, Academy of Finland Research Fellow in the Department of Biosciences at Åbo Akademi University, said over the past few decades concern has been mounting over EDCs, and that their contamination of aquatic habitats is a serious environmental problem.

"Endocrine disrupting chemicals (EDCs) are cause for concern given their capacity to disturb the natural functioning of the endocrine (hormonal) system, often at very low concentrations, with potentially catastrophic effects.

Research until now has focussed primarily on the morphological and physiological effects of EDC exposure. For the first time, our research has shown that exposure to an environmentally realistic concentration of 17β-trenbolone -- just 22 nanograms per litre -- is sufficient to alter male reproductive behavior."

The research shows that exposure of guppy fish to 17β-trenbolone influences the ratio of male courtship (where the female chooses her mate) to forced copulatory behavior (sneaking), whereby the female is inseminated internally from behind and does not choose her mate. The results of her research indicated a marked increase in sneaking behavior.

"By influencing mating success, sexual selection can profoundly affect individual populations and species, with potentially devastating long term evolutionary and ecological impacts," Saaristo said.