How pollution alters the sex lives of fish

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red sea flasher wrasse (paracheilinus octotaenia

Image: Shutterstock/stephan kerkhofs

As pollution continues to take its toll on the earth and all its inhabitants, some recent research has focused on the ways aquatic life in particular is being harmed. Since carbon dioxide, a key factor in many aspects of pollution, increases acidity when absorbed into the oceans, the effects of increasing sea acidity levels is a growing concern among scientists. One realm of study looks at fish behavior, namely mating or other sexual behaviors, as altered by acidity levels, and finds that some fish are facing significant changes in their sex lives.

What’s happening to the fish?

Some fish are being rendered unable to adequately sense signals necessary for effective sexual selection, which are emitted by the opposite sex and are indicative of preferable mating traits or conditions. One such fish, the threespine stickleback, has been studied for its breeding behaviors in the laboratory. The stickleback have red markings and nest-building skills typically identified as essential in their courtship traits and behaviors. In tests designed to assess mating behaviors in clean versus more polluted water, results showed significant changes in visual signals sent by males and more relaxed sexual selection associated with the polluted water. In the dirty water, males would be received by females often regardless of their trait quality—which didn’t limit their offspring, but did limit their offspring’s viability.

Another recent study focused on the mating behaviors of male ocellated wrasses, fish known for building nests prior to mating. The fish behavior monitored near wrass nests closer to high carbon dioxide regions near volcanoes was compared to mating behaviors near wrasses’ nests approximately 100 miles away from the volcanoes. Underwater videos of the fish revealed that more dominant male wrasses mated less frequently in the higher carbon dioxide concentrated regions—however, they still sired plenty of eggs in the nests they protected. Regardless, the revelation of any change in behavior is startling for scientists to acknowledge, prompting the ultimate concerns to be centered around the possibility of eventual population decline overall.

Why should we care?

A greater understanding of all the factors involved with animal behavior, including sexual selection, mating behaviors, and all that which is geared toward continuing the species’ existence, is illuminated as crucial when we examine it all through the lens of a deteriorating environment. As we continue to learn what changes can be determined through studies like these on the ever increasing levels of carbon dioxide entering our world, it seems a vital piece of evidence is always presenting itself. Taking steps to lower one’s carbon footprint makes a difference in every area of the globe.

Kristen lives in the Michiana area, where she enjoys lake-effect weather, apple orchards and occasional South Shore rides into Chicago. She can probably tell you more about apple cider vinegar than you'd ever want to know. You can reach her at:

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