Organically fish smell but metals contaminating the environs that fish live in destroy their ability to smell. A Canadian study demonstrates that fish can recover their sense of smell with remediation of lakes and streams. Here is an excerpt from Scientific America explaining this restorative process: Greg Pyle, a professor at the University of Lethbridge in Alberta, said he suspects that impaired sense of smell “has meaningful and profound effects” on many fish species. It may be jeopardizing entire populations of fish, including some endangered species. “We’ve tested everything from leeches to water fleas to several species of fish,” Pyle said. “Every species and every metal we’ve observed has had effects at low, environmentally relevant concentrations.” Most contaminated lakes have a metallic mix, making it hard to tease out which pollutants are to blame. In the latest study, Pyle and his team of researchers took yellow perch that lived in Ontario lakes contaminated with mercury, nickel, copper, iron and manganese, and put them in a cleaner lake. Within 24 hours of basking in the clean water, the fish regained their sense of smell. This shows “fish from metal contaminated lakes have the ability to recover once the lake recovers,” the authors wrote in the paper published in last month’s Ecotoxicology and Environmental Safety journal. The researchers used wild fish from two lakes with metal contamination (Ramsey and Hannah lakes) and from a cleaner one (Geneva Lake). Ramsey and Hannah, located in Sudbury, Ontario, are polluted from more than a century of mining, particularly with nickel. Hannah Lake is one of the worst-polluted lakes in the area, while Ramsey is similar to other North American lakes near industrial areas. Geneva Lake is far enough northwest to escape most contaminants. Just as the clean lake revived the sense of smell for the Ramsey and Hannah fish, Geneva Lake’s perch had decreased smell after just 24 hours of hanging out in the dirtier lakes. Their response times to substances that smelled like their food dropped 75 to 59 percent. http://www.scientificamerican.com/article.cfm?id=fish-cannot-smell-in-polluted-waters