Tiny Minnows have grown to Endure extreme Pollution

Toxic waste is, well, toxic to marine life. But there is at least one species of small fish that has become resilient to extremely high levels of industrial pollution … to the point of being almost miraculous.

Living in four heavily polluted estuaries on the East Coast of the United States are small and nondescript “mud minnows,” or Atlantic killifish, which local fishermen often use as bait. Thanks to an evolutionary mutation, these fish have grown to endure conditions in extremely toxic water, permeated by very high levels of industrial pollution that would be lethal to any other species, scientists say.

The small killifish not only survive but positively thrive in these waters, researchers have found. “You see killifish at these sites that are extremely tolerant of some very nasty chemical pollutants,” explained Andrew Whitehead, an environmental toxicologist from the University of California who was the lead of a study on the fish published in the journal Science.

These estuaries have been badly poisoned for over a half century with the poisonous soup of dioxins, polychlorinated biphenyls (PCBs), mercury and heavy metals in them being up to 8,000 times the normal level. Whitehead and his colleagues collected some 400 killifish from New Bedford Harbor in Massachusetts, Newark Bay in New Jersey, the Bridgeport area of Connecticut, and the Elizabeth River in Virginia to see how these fish can endure in these areas.

The scientists then sequenced the genomes of fish from the polluted estuaries and compared them to genomes of killifish living in unpolluted waters nearby. What they discovered was a common set of mutations in the toxin-tolerant fish that turned off a molecular switch that would have made them liable to cellular damage caused by the chemicals. However, this advantage has come at a cost to the fish: genetically they have become less diverse, which means they may be more prone to suffer collectively from other environmental stressors in future.

On the one hand, the finding has shown that certain animals will be able to adopt to extreme man-made pollution by undergoing genetic changes. On the other, however, it has also shown that these changes will be limited only to a few species and even those species may end up suffering long-term genetic harm from these very changes. The solution to this conundrum is simple, of course: we will need to stop polluting our rivers, seas and other ecosystems once and for all.