This Fish Has Adapted to Toxic Waters That Should Kill It

Thanks to rapid evolution, the Atlantic killfish can survive in an environment filled with toxic pollutants.

Populations of Atlantic killfish living in highly polluted estuaries on the East Coast have found a way to make a living in waters that should normally kill them, according to researchers from the University of California, Davis.

Writing in the journal Science, the researchers say killfish living in long-polluted waters off Massachusetts, Connecticut, New Jersey, and Virginia were a whopping 8,000 times more resistant to the toxic industrial pollutants than other fish. In short: The fish should by all rights be dead, except they're not.

How do they do it? It's in their genes.

The researchers sequenced the complete genomes of close to 400 killfish from the sites (their waters sullied since more than half a century ago by industrial heavy metals and other pollutants) and found that a high degree of genetic variation – higher than any other vertebrate – let them evolve rapidly in response to a fast-changing environment that became contaminated.

Importantly, the fish made the changes in similar ways, genetically speaking, which told the researchers that the animals already carried within them the genetic variation necessary for life in the toxic water.

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While the killfish doesn't have value to commercial fishermen, the UC Davis finding makes them important for people because of what might be learned from the fish's particularly hardened sensitivity to chemicals.

"If we know the kinds of genes that can confer sensitivity in another vertebrate animal like us, perhaps we can understand how different humans, with their own mutations in these important genes, might react to these chemicals," said Andrew Whitehead, lead author of the study, in a statement.

The researchers threw up one flag of caution surrounding their work. We shouldn't, they suggest, get too excited about the killfish's adaptability in terms of other species getting by in the same way in the 21st century.

"Some people will see this as a positive and think: 'Hey, species can evolve in response to what we're doing to the environment.'" said Whitehead. "Unfortunately, most species we care about preserving probably can't adapt to these rapid changes because they don't have the high levels of genetic variation that allow them to evolve quickly."

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