Name: Oncorhynchus mykiss

Native Range: Native to North America, Rainbow trout can be found in streams and lakes west of the Rocky Mountains from Alaska to Mexico. 

Introduction: Rainbow trout are a favorite of anglers, and as a result are now one of the most widely introduced fish species in the world. They are staples of many sport fisheries and have been intentionally introduced in many sites worldwide to “improve” fish stocks for anglers and to supplement aquaculture. Now, they’re found on every major continent except Antarctica. 

Photo credit: User: JCVD100 / Flickr

Photo credit: User: JCVD100 / Flickr

Why are they harmful?: Anglers may like them, but rainbow trout are bad news for native fish. They compete with native brook trout and Atlantic salmon for food and habitat, which can drive native species to migrate away from their native habitats. Rainbow trout also hybridize with other, less abundant trout species, ultimately impacting the species’ genetic makeup. This has led to the near-extinction of multiple trout species. Additionally, stocking of hatchery rainbow trout has led to the introduction of whirling disease, a parasite that causes fish to swim erratically and experience difficulty feeding, in about 20 states. 

Methods of control: Although some areas still intentionally stock rainbow trout, other areas are attempting to cut down on rainbow trout numbers. There are two main methods to remove the fish: fish traps and electro-fishing. Electro-fishing only stuns the fish, so it has the added benefit of allowing scientists to monitor populations of other fish while also removing rainbow trout. These methods are currently employed by rangers at the Grand Canyon National Park, where they’re attempting to remove non-native trout to help the recovery of the native humpback chub. 

Sources: NPS, USGS, GCNP, ISGG 

Photo credit (cover photo): Latham Jenkins