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Swordtail Scent

When it’s time to choose a mate, odor is everything.

At least, for the female swordfish it is. Confused by competing odors in the Rio Calnali in northeastern Mexico, female sheepshead swordtails are starting to stray, mating with a cousin species known as highland swordtails and creating a whole new hybrid breed.

Researchers found the sheepshead swordtails will only pick their own kind when swimming in clean waters. And the Rio Calnali is anything but. In recent years, untreated sewage and agricultural runoff have created lots of organic matter, which produces humic acid when it degrades. One whiff of that humic acid and the male swordtails find themselves on the losing end of the mating game. It seems they just don’t emit a powerful enough odor to lure the females away from the stronger-smelling highlands.

Scientists found that the hybrid offspring are also able to reproduce, perhaps even better than the parent species. That means the hybrid species could well take over, even if water conditions were to return to normal.

There are other reasons to keep water free of agricultural runoff and sewage, of course. Bacteria from untreated sewage can cause diseases such as E. coli, while pesticide residues in agricultural runoff cause harm to both humans and aquatic life.  

For more information on the swordtails, click here.

To read more about this and other environmental health issues, go to www.environmentalhealthnews.org, www.ourstolenfuture.org or www.healthandenvironment.org.