How the use of MT in aquaculture could affect humans or wildlife is apparently largely unknown. (Photo: Universidad Juarez Atuónoma de Tabasco)
Bacteria could protect tilapia farmers and nearby ecosystems
Thursday, October 14, 2010, 01:00 (GMT + 9)
Mexican researchers have discovered that three common bacteria species ravenously eat the potentially dangerous steroid methyltestosterone (MT) which aquaculture farmers use to change the sex of their tilapia.
The finding may lead to a safer environment for workers as well as residents and wildlife near farms, and has a global reach because tilapia is raised in over 100 countries, reports EP Magazine.
Tilapia farmers add MT to the powdered fish food they give tiny tilapias, or fry, daily for three to four weeks to turn them into males. Males are desirable because they grow faster than females and to prevent reproduction by keeping one sex only.
Fry swallow MT and then excrete it back into the water.
Fish biologist Wilfrido Contreras Sanchez -- who heads the biological sciences division at the Autonomous Juarez University of Tabasco where the bacterial research was done -- is concerned that the steroid’s residue might impair the health of workers who enter the water to gather juvenile fish. Further, many farmers discharge the tainted tank water into natural bodies of water where it might harm wildlife.
The health of locals who swim in or wash their clothes in the waters might also be jeopardised, he said.
How the use of MT in aquaculture could affect humans or wildlife is largely unknown, he told.
MT is an androgen given to rouse puberty in slow-developing adolescent boys and to treat breast cancer. Notably, the US Food and Drug Administration (FDA) has said that extended use of androgens in high doses has been linked with liver cancer development, and that androgens may increase elderly people's chances of getting prostate cancer.
In women, high doses can breed deeper voices, facial hair, acne and irregular menstrual cycles, the FDA warned.
Contreras is hopeful that the bacteria in the study will eradicate potential dangers if added to the water filters in the tanks in high enough amounts.
The team intends to run additional experiments to determine how many bacteria to use, what species to use and how long to let them eat. The university may then be able to grow heaping quantities of the selected bacteria and sell the microorganisms to tilapia farmers in the form of a concentrate, he said.
Another finding was also achieved by the researchers: the fish in the tanks with P. aeruginosa weighed more than the fish from tanks without the bacteria. P. aeruginosa could be one of the species that boosts growth in aquaculture systems.
The research received funding from Oregon State University, the University of Arizona, the Autonomous Juarez University of Tabasco and the US Agency for International Development through its AquaFish Collaborative Research Support Programme.
By Natalia Real