How do some fish swim in polluted, toxic waters and still survive? It's in their genes, according to Joanna Kelley, a genome scientist from the School of Biological Sciences at Washington State University. Scientists are calling these special types of fish "extremophiles" because they are able to actually adapt to their septic environment when few fish can.  

Kelley and scientists from Stanford University, Kansas State University and Universidad Juárez Autónoma de Tabasco evaluated Atlantic mollies in southern Mexico. These tiny fish (slightly over one inch in length) live in tropical freshwater, brackish water, and acidic springs contaminated with hydrogen sulfide-a byproduct of nearby volcanic activity. They compared the gene expression in fish living in each location for the study, now published in the scientific journal Molecular Biology and Evolution.

"In the freshwater system, there are 30-plus species of fish," Kelley said in an official statement. "In the sulfidic springs there's the molly."

Of the extremophile molly's 35,000 genes, 170 of them were "turned on" to rid itself of hydrogen sulfide. These genes have actually been connected with hydrogen sulfide detoxification by scientists in other studies-which Kelley found very exciting.

This finding will assist researchers in understanding just how fish evolve to live in polluted waters-many of which are now human induced.

"In these habitats, the natural pollutants give us a glimpse into the future and help us think about what happens in ecosystems that suffer from human-induced changes or pollution," Michael Tobler, a co-author and assistant professor at Kansas State University, said in the release. "We can learn how an ecosystem changes when pollutants are added and how organisms cope with that."

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