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We Keep Giving Accidental Sex Changes to Fish

It's not just your birth control-tainted urine forcing fish to suddenly swap sexes. A recent study has found that a common steroid used to bulk up beef is giving aquatic life sex reversals.

Surely you recall the unsettling news we shared this March that birth control pee is giving ovaries to male fish. Well, apparently there's no end to the piscine gender-benders caused by manmade drogas. A new study on shows that a steroid we feed cattle is also giving sex change transitions to fish.

The study is a bit dense—its title is "Coupled reversion and stream-hyporheic exchange processes increase environmental persistence of trenbolone metabolites"—but the main thrust is alarming. In essence, a very common livestock drug, thought to be generally harmless, is wreaking havoc on vulnerable aquatic life.


The drug in question is called trenbolone acetate (TBA), a steroid that's verboten for weightlifters but cool for cattle. The researchers say its use is "ubiquitous" among conventional beef producers, a low-cost way of jacking up body mass. The hormones are estimated to cut costs by about 7 percent—an annual $1 billion in savings, nationwide.

The working theory has long been that sunlight neutralizes any funky side effects from this steroid. Once dispersed into the farmland ecosystem, TBA was thought to be mostly benign. Not so!

A 2013 study by the same researchers showed that sunlight doesn't, in fact, decontaminate TBA. Light does render the drug inert, but only temporarily. In the darkness—like some B-movie ghoul—TBA regains its power.

And what power it is. "At very low levels, trembolone acetate has been documented to cause partial or incomplete sex reversals in fish, to decrease reproduction rates in fish, and to alter their endocrine system," lead researcher Adam Ward told CNBC.

Some fish farmers actually feed TBA-like drugs to their fish on purpose; it can prevent pesky breeding by turning everyone male. That shady practice is an ethical discussion for another day, but it certainly seems incontestable that this we don't want TBA streaming through our waterways unchecked.

Of course, there are lots of manmade chemicals that could disrupt the aquatic ecosystem; Ward cites Viagra, caffeine, and ibuprofen as examples. And, as mentioned earlier, estrogen-spiked pee can give a male fish ladyparts. Big-picture takeaway? Tread lightly, humans.

In semi-related news, a goldfish named Monty just underwent 45-minute surgery to get some tumors removed. It was Monty's third operation.

Watch: The Politics Of Food on Bluefin Tuna