Rainbow trout - among 100 "world’s worst" invaders

Authors: Invasive Species Specialist Group of the International Union for Conservation of Nature

Similar to the brown trout, anglers have irresponsibly released trout into rivers and streams world-wide. This can wreak havoc on an unexpectant wildlife, through competition, predation, and diseases such as whirlings disease. Native fish, invertebrates, frogs, toads, newts, and snakes have all suffered.

"This species has been nominated as among 100 of the "World’s Worst" invaders."
anglers encourage alien fish - rainbow trout

RELEASED For recreational anglers to catch

"They are the basis of many sport fisheries and are highly sought-after by anglers. In many locations rainbow trout are raised in hatcheries, then liberated into rivers and streams for recreational anglers to catch."

"One of the most widely introduced fish species in the world. Native to western North America, from Alaska to the Baja Peninsula, Oncorhynchus mykiss have been introduced to numerous countries for sport and commercial aquaculture."

"Highly valued as a sportfish, with regular stocking occurring in many locations where wild populations cannot support the pressure from anglers. Concerns have been raised about the effects of introduced trout in some areas, as they may affect native fish and invertebrates through predation and competition."

Whirling disease is a condition caused by a protozoan that causes dysfunction in the nervous system of salmonids, and may result in curvature of the vertebral column. This results in fish losing the ability to maintain a proper orientation, causing them to swim in a spiral motion. The stocking of hatchery-reared trout into the wild has caused outbreaks of this disease in the United States, threatening wild fish populations."

"In many countries introduced rainbow trout have been reported to have negative effects on native fish, amphibians and invertebrates."

"In New Zealand it is suspected that rainbow trout affect native fish species through direct predation and competition for feeding areas, while in the United States there is evidence that the same is happening to fish such as the humpback chub, suckers, and squawfish."

"Impacts include hybridisation, disease transmission, predation and competition with native species. In the United States, the introduction of rainbow trout into areas outside of their native range has caused problems due to their ability to hybridise with native salmonid species, affecting their genetic integrity. Some species, such as the Alvord cutthroat have become virtually extinct because of this. Other species known to be affected by hybridisation include the Lahontan cutthroat trout; golden trout; Gila trout."

"Competition: Introductions of non-native fishes can lead to the decline or extinction of native species through interspecific interactions. In particular, many species of salmonids have been introduced into streams throughout the world, primarily for recreational fishing. Closely related native and introduced salmonids have not coevolved to partition niches, thus interspecific competition can often occur between such species."

Yosemite National Park (USA)
"Reduction in native biodiversity. The results of the current study provide strong evidence that in Yosemite National Park, introduced trout have profoundly altered the distribution of two mountain yellow-egged frog and Pacific tree frog of the four native aquatic-breeding amphibians, the other two being Yosemite toad and Sierra newt, and both of the widely distributed garter snake species, Mountain garter snake and the Sierra garter snake."
Fish Pain