Hakai Magazine

Coastal science and societies

a barramundi fish underwater
Like a drug, ocean acidification might impair the barramundi’s ability to tell safety from danger. Photo by Kim ChongKeat/Shutterstock

Fish on Acid Have Their Senses Confused

Acidic water affects how one fish species parses sight, smell, and sound—a potential sign of neurological disruption.

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by Amorina Kingdon

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This is a story about what happens when youth are exposed to acid. Their brains are chemically altered until they’re all out of whack. They flee from their safe, traditional homes. They gravitate to dangerous places, and even more dangerous friends. The youth in question are larval barramundi, and for them, too much acid is a big problem.

Most barramundi—also called the Asian sea bass—are born near a river’s mouth. They drift in the sea as larvae, and then grow up near the shore. The common, meter-long fish spend their youths hiding in sheltered areas along the coast, such as in the tangled roots of a mangrove forest. To find their way from the open sea to this sanctuary, they need to draw on their senses to navigate through the unknown and avoid the risks of predation and death.

In new research, however, Ivan Nagelkerken, a marine ecologist at the University of Adelaide in Australia, found that when he exposed captive barramundi larvae to acidified water, the fish fled from safe sounds and gravitated toward unsafe ones, a change that could have lethal consequences for wild fish.

Nagelkerken already knew from existing research that some fish, including the barramundi and clownfish, appear to change their preferences for sights and smells when exposed to acidified water, but he didn’t know the exact mechanism driving the apparent sensory impairment. He also didn’t know if acidification affected the fish’s hearing in the same way. If barramundi could still decipher danger by sound, they might still thrive in a changing ocean.

To find out, he gave captive barramundi a series of hearing tests. He played the fish three soundtracks: the soothing burbles of a safe mangrove forest; the cacophony of a rocky reef; and the dense hiss of artificial white noise, which simulated boats and other human-generated sounds.

He found that fish larvae swimming in regular seawater avoid the reef and white noise. But when he exposed them to water with the same acidity levels as is predicted for the end of the century, the barramundi swam toward the rocks and white noise, and away from the mangrove sounds.

With acid seeming to affect multiple senses, Nagelkerken says it’s becoming clear that acidification is having an effect on the fish’s neurology, and isn’t just causing a simple sensory impairment. Similar to how the seemingly disparate symptoms of blurred vision, excessive thirst, and fatigue can be a sign of diabetes in humans, he suspects the apparent confusion in senses is an underlying issue—in this case, neurological disruption. Though, this idea has yet to be proven.

So, are barramundi doomed—victims of a bad acid trip? That’s still unclear.

Isabelle Côté, a marine biologist at Simon Fraser University in British Columbia, says that while the switching effect is intriguing, it’s inappropriate to assume the effects of acidification will manifest exactly the same in the wild, as the ocean is far more complicated than a tank. And in the experiments, the larvae were exposed to a sudden, shocking shift in acidity—an unlikely occurrence in the wild. “In real life, those organisms are going to have generations—100 years—to get habituated,” Côté says.

Nagelkerken says that while the change in acidity won’t be instantaneous, it may still overwhelm fish that need time to adapt. “If the changes are too fast, you simply can’t get sufficient adaptation to support populations.”

Ultimately, as with many a cautionary drug PSA, the picture painted by these studies is probably a little exaggerated. But if the mind-altering effects that hit wild fish are even a little similar, that’s not cool, man.