Canada’s Transsexual Fish

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It just got harder to be a fish—at least a Canadian fish. Or at least a Canadian fish looking for a mate. That’s because more and more of the boys keep turning into girls. As with so many other things, it’s humans who are to blame.

The human household environment is awash in chemicals—preservatives, plastics, drugs, cosmetics and more. A lot of those chemicals contain hormones or so-called endocrine disrupters, and many of those gender-manipulating substances wind up getting washed down drains or flushed down toilets and into streams, rivers and other waterways. Numerous studies over the years have shown that this can have an impact on the sexual development of fish, amphibians and other aquatic life, but a new Canadian report in Environmental Toxicology and Chemistry has turned up some especially striking findings.

Investigators in Alberta studied two bodies of water in the South Saskatchewan River basin: the Red Deer River and the Oldman River. The scientists screened the water for more than two dozen drugs including birth control medications, BPA (an endocrine disruptor found in plastics) and agricultural chemicals including steroids used in raising animals. They found more than enough of the alien chemistry to cause them concern. They also found that at 14 of 15 locations, male fish exhibited elevated levels of a protein typically found only in female fish—one that’s used mostly when they’re producing eggs.

What’s more, it wasn’t even all that easy to find the males to study. The fish populations both upstream and downstream of human communities were pretty much the same, but their gender ratios weren’t. Upstream—where fresh batches of chemicals weren’t regularly getting dumped into the water—the gender balance was 55% female and 45% male. Downstream it was a startling 85-15. Said Lee Jackson, one of the paper’s co-authors:

“The situation for native fish will likely get worse as the concentration of organic contaminants become more concentrated [due to] the increase in human and animal populations. What is unique about our study is the huge geographical area we covered. We found that chemicals…that have the potential to harm fish were present along approximately 600 km [370 mi.] of river.”

As long as at least some males survive and are free to travel anywhere in the river, the overall breeding stock of the effected fish species should not suffer too much. But ultimately a tipping point will be reached at which an overwhelmingly female population won’t be able to do all the  reproducing it needs to do to survive. Extinction is not an unusual result of humanity’s mishandling of the planet, but even for us, this will be an unusual way of achieving it.