The Surprising Reason Fish Can’t Smell

Polluted water can also potentially alter a fish’s ability to find food and reproduce—and makes them more vulnerable to predators.

yellow perch
Without its sense of smell, the yellow perch is swimming an uphill battle for survival. (National Geographic/Getty Images)
A former Gourmet staffer, Lawrence enjoys writing about design, food, travel, and lots of other stuff.

Maybe you’re familiar with the concept of bioaccumulation. Then again, maybe you’re not. Basically, one species, fish for example, ingests toxic substances, which are then passed up the food chain to birds, other animals, and eventually all the way to people.

Now research reveals that the fish themselves are also showing the side effects of exposure to polluted waters. A recently released study found that fish in lakes tainted with metals are losing their sense of smell.

“The effects we’ve been seeing are quite ubiquitous, in that they occur with every animal we’ve tested, in every communication system we’ve tested, and for every metal we’ve tested,” Dr. Greg Pyle, a professor at the University of Lethbridge in Canada, tells TakePart. 

“Although we do study basic toxicological effects—such as mortality, growth, reproduction, or physiological condition—effects on chemosensory function are very sensitive to metals and likely lead to ecologically meaningful effects,” says Pyle.

Pyle explains that fish rely on chemosensory information, “basically smells that contain information,” for finding food, avoiding predators, or for mediating reproductive behaviors, among other things such as migration and establishing social hierarchies.

“These are vital life processes,” says Pyle. “Anything that can disrupt a fish’s ability to perceive these ecologically important cues has the potential to cause ecologically meaningful effects—starvation because the animal couldn’t find food, increased vulnerability to predators if a fish can’t detect that there’s a predator nearby, or failure to reproduce if it can’t detect reproductive pheromones from potential mates.”

Interestingly, if the fish are transferred to cleaner water—even if they’ve been exposed to pollutants their whole life—their sense of smell returns. As part of their study, Pyle and his team took yellow perch that lived in Ontario lakes contaminated with mercury, nickel, copper, iron and manganese, and put them in a cleaner lake.

The result: The fish regained their sense of smell in just 24 hours.

Pyle was surprised by these findings and notes that, “We don’t understand yet what ‘recovery’ means in these natural systems. We’re not sure if fish from the contaminated systems have simply adapted to chronic metal exposure or that the presence of the metal in the olfactory chambers simply inhibits the olfactory tissues from firing in the presence of an odor. We’re exploring these and other mechanisms in the same fish populations this summer, where our focus will be almost exclusively on understanding chemosensory recovery in metal-contaminated fish.”

However, Pyle says that earlier work in his lab demonstrated that when fish are exposed to relatively low, environmentally-relevant metal concentrations during a sensitive developmental stage, their chemosensation can be impaired permanently.

“Since we know that metal-impaired chemosensory function can recover in adults, we’re recommending that delaying the release of metal-containing effluents to spawning or nursery areas could do much to protect populations against long-term chemosensory impairment.”

Of course, it would also be helpful if we could find a way to simply keep pollutants out of our lakes to begin with.

How can we draw more attention to this problem and curb the release of pollutants into our lakes?

Lawrence Karol is a writer and editor who lives with his dog, Mike. He is a former Gourmet staffer and enjoys writing about design, food, travel and lots of other stuff. @WriteEditDream | Email Lawrence | TakePart.com

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