Holy mackerel! Pollution has startling effects on nearby wildlife

If you’ve ever watched an episode of the X-Files (or you’re a self-proclaimed super fan, like myself) you might have been intrigued by the idea of spooky biological abnormalities creeping into cheesy 90’s culture. The show often features frightening hybrid creatures born out of profound human error such as the “Flukeman,” a human/worm monster, a product of the chernobyl incident, who must now feed on humans to reproduce — or so Scully and Mulder think.

But sci-fi nerds around the world have been enticed, and haunted, by the fact that strange biological phenomena are popping up offscreen, all around us. From waterfowl deformities and die-offs at the Kesterson Reservoir, to mass vulture deaths in South Asia, to chunks of meat falling from the sky in Kentucky, these eerie happenings are all too often linked to byproducts of humans. While flocks of birds falling from the sky are difficult to miss, a close look into a neglected stream will reveal strange developments in hidden creatures underneath the surface.

Something’s fishy here…

Over the past few decades, scientists have become more and more interested in an eerie happening in fish biology. This phenomenon, termed intersex, occurs when an animal develops both sperm and eggs within the reproductive organ. Usually, we see intersexed males, who now produce eggs in addition to sperm.Though the jury is still out on what factors are most important in the development of intersex, we know that these reproductively mutant fish pop up in a variety of aquatic environments on nearly every continent.

What’s causing this global rise in intersex?


While some scientists argue that occasional observations are to be expected naturally, most recognize intersex as a red flag indicating contamination. If a water supply is contaminated, fish that exist entirely in that environment are overexposed to those contaminants. Humans can also be affected by water contamination, though to a lesser extent by virtue of less exposure. You’re probably familiar with the effects of water contamination on humans, given the recent uproars about lead-filled tap water in Flint, Michigan and the horrific wastewater spill that turned the Colorado river bright yellow, but contamination effects on aquatic animals can be just as damaging to aquatic animals.

These contaminants come from a variety of places, from your grandmother’s farm to the neighborhood drugstore, but almost all of them end up in the same place — waterways. Many of these contaminants contain harmful hormone disrupting chemicals that are directly linked to intersex in fish. And if that’s not unsettling enough, fish exposed to urban water have been found to contain other disconcerting substances in their systems, such as painkillers, caffeine, and anti-depressants, which may not result in intersex, but certainly aren’t naturally found in aquatic systems.

Why should we care about intersex in fish?

Intersex reduces successful fish reproduction. Effectively, males expend energy developing eggs that they can’t use, which has a negative effect on their ability to create sperm that they can use. These negative effects come in two varieties: less sperm and crappy (ha!) sperm. As biology goes, sperm are small and cheap  while eggs are big and expensive. So, much like running a marathon in the morning tires you out for the rest of the day (or week…), producing costly eggs makes it difficult for fish to also produce high quantities of sperm. They just don’t have the energy. And beyond the obvious spatial consequences of shoving a handful of marbles into a small bag of sand, these less numerous sperm are also less mobile. In terms of fish reproduction, this means they’re worse at reaching an egg. All in all, fish reproduction via intersex is terribly inefficient and can negatively affect populations that have high rates of intersex.

An optimistic outlook

So, mutant fish are popping up in streams worldwide and are less capable of propelling the population into the next generation. Though this may seem like a dismal look into the future of our recreational fishing and seafood industries, scientists are on the case! Researchers are studying the consequences of contamination, and water treatment methods are becoming more effective as a result.  As technology and science progress together we can aim to balance human advancement and wildlife protection. These solutions can be hard to find or tricky to engineer, but they’re out there somewhere. I want to believe.

About the Author:

Kaleigh Davis is a lab technician in the plant biology department at UGA. She graduated from the Odum School of Ecology in 2015 and is a lover of all things aquatic. Her career goals include getting a PhD in marine ecology and learning to do a headstand. For now you can find her sipping on coffee at all hours of the day or zigzagging around town watching birds overhead. Get in touch with Kaleigh at kaleighedavis@gmail.com. More from Kaleigh Davis.