Scientists from the National Marine Fisheries Service (NMFS) and leading universities in the United States and Canada published a study in the journal Science News demonstrating the negative effects of water pollution on the sense of smell in fish. Fish have heightened senses of smell, which allows them to hunt for food, discover mates, and avoid predators. However, the recent report highlights that water pollution disrupts the fish’s ability to smell correctly and receive important neural cues from the smells.

Most west coast school children love the fact that salmon smell their way home to spawn. Unfortunately, the NMFS study demonstrates that exposure, as short as a couple of hours, can "interfere with olfaction" for Coho salmon (Oncorhynchus kisutch). The study tested trace amounts of common metals and pesticides that are found in salmon streams. Varying levels of the pollutants were injected into water surrounding fish. As the amount of pollutants increased the severity of negative consequences also increased, a mere 100 parts per billion of pesticide removed all neural responses to smell. The most common herbicide, glyphosate an active ingredient in Roundup, used in the United States severely stunted a fish’s ability to smell. The effected Coho were less able to: navigate in the dark and predict danger.

When generic pesticides, rather than just the active ingredient, were tested the effects on fish increased. Therefore, the inert ingredients, which companies are not required to list for proprietary reasons, had a compounding effect on fish sense of smell. Christian E. Grue, from the University of Washington, estimates that "4.1 billion pounds of inert [pesticide] ingredients are applied annually" in the United States. A large amount of pesticides are placed on agricultural fields annually. Unfortunately, even just trace amounts of these ingredients may have large impacts on fish, making it harder for them to eat, easier to be preyed upon, and tougher for them to find a mate and spawn. Numerous other studies of the impacts of trace metals and pesticides on fish have been studied in other aquatic species, yellow perch, Chinook salmon, fathead minnows, and water flea.

Researchers found that a reduction in Coho sense of smell passed within a few hours, but when fish were exposed to continued pulses of pollutants they were unable to recover their sense of smell. The results from this study shed light on one more negative environmental impact that salmon, and other fish, must overcome to survive in the streams that we have left for them. For more information about the Science News Vol.171 No.4 article see www.sciencenews.org/articles/20070127/bob10.asp.