Rainbow Trout (Photo US EPA)

Rainbow Trout (Photo US EPA)We have previously described some nasty flora and fauna in this column, but this article deals with one of our better liked species, the rainbow trout. I have spent many enchanting hours drifting a dry fly over a rainbow trout, both locally and in more exotic locales. It was not until I read An Entirely Synthetic Fish, by Anders Halverson, that I determined that rainbow trout might be characterized as an invasive species.

Rainbow trout are native only to the Pacific Rim, from Mexico to Russia. Fish culturists learned how to artificially breed rainbows and they were first introduced in a California stream in 1872. At about the same time, the United States Fish Commission was established and stocking rainbow trout that soon became the rage throughout the country. They were introduced in lakes and streams that were devoid of fish or that contained only “rough” fish, disdained by sporting anglers. Rainbow trout were also introduced in streams that contained other, native, species of trout.

Rainbow trout can withstand higher temperatures than other species of trout. This is important because excessive logging turned many cool forested streams into hot tubs, no longer capable of sustaining native trout.

Rainbow trout have been spread throughout the world. They are included in the top 100 of the world’s worst invasive species. Research has shown that they can displace native trout, and their sheer numbers can alter the aquatic invertebrate community, to the detriment of other fish species. Their impact on native fish seems to be greatest in places that never had trout (Australia and New Zealand, for instance).

For every person born in the United States every year, federal and state hatcheries raise and stock 20 rainbows into public waters. Fish culturists can manipulate genes through breeding programs so that there are presently more than 75 strains of rainbow trout. Rainbows are bred for traits like the time of year that they spawn, their growth rate and their tolerance for temperature and disease.

While it is true that rainbow trout have an unfair advantage over native species of trout, few advocate that we do away with rainbows. Many, however, have a great preference for “wild” trout, which are entirely different from “native” trout. A wild trout is a product of natural reproduction. It is quite common to have a wild trout that is not native. Many natural resources departments throughout the country are turning away from stocking hatchery bred fish and devoting more money and effort into improving stream habitat, so that wild trout may prosper. Such action can only be better for all who are concerned about nature.