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At the Autonomous Juarez University of Tabasco in Villahermosa, Mexico,
scientists have conducted some ground-breaking research that could be good news for the environment
and the tilapia fish industry.
They've identified three common species of bacteria
that break down methyltestosterone,
also known as MT.
It's a potentially harmful steroid that fish farmers use to change the sex of tilapia.
Tilapia producers add the hormone to the powdered food they dish out to large tanks
of tiny tilapias
to turn them into males.
They want males because they grow faster than females
and because having only one gender prevents reproduction.
The young tilapias swallow the steroid
but then excrete it back into the water through their feces and urine.
This water is then often discharged into streams,
rivers and lagoons.
Fish biologist Wilfrido Contreras Sanchez
worries about the safety of this hormone-laced water, although little is known about its impact.
"After releasing the effluents, other targets may be affected like frogs, fish
or even humans."
Contreras hopes that the bacteria he studied
will eliminate potential hazards if added in sufficient amounts to the water filters
in the tanks where the tiny tilapias dine on MT.
With funding from the U.S. Agency for International Development
through its AquaFish Collaborative Research Support Program,
Contreras and fellow researchers found
that Pseudomonas fluorescens and Bacillus ceresus each removed 99 percent
of the hormone
after 20 days in flasks.
Another species, Pseudomonas aeruginosa,
devoured 97 percent of the hormone after 16 days in flasks.
Researchers then added Pseudomonas aeruginosa
to filters that cleaned the water of large concrete tanks where young tilapias were fed MT.
The trial showed a trend toward lower levels of MT over time in the tanks where bacteria
had been added versus the control tanks without bacteria, Contreras said. He and his team
plan to conduct more experiments to fine tune how many bacteria to use,
what species or combination of species to use, and how long to let them feast.
"I'm really interested and looking forward to see
if we can start working with some farms and take it to the next level. We have done it
at the laboratory level
and I think we need to start working with the farms to see
if we can do a mass production of this."