Rainbow trout

Lore & Background

The rainbow trout was originally named by German naturalist Johann Julius Walbaum in 1792 based on specimens from the Kamchatka Peninsula in Siberia, using the local name mykizha. Later, Sir John Richardson named a specimen Salmo gairdneri in 1836, and William P. Gibbons named a population Salmo iridia in 1855. These names were superseded when Walbaum's description was recognized as having precedence. In 1989, morphological and genetic studies moved the species from the genus Salmo to Oncorhynchus, aligning it with Pacific salmon.

Adult freshwater rainbow trout average between 0.5 and 2.5 kilograms, while lake-dwelling and anadromous forms may reach 9 kg. Coloration varies widely; adult fish have a broad reddish stripe along the lateral line, most vivid in breeding males. Juvenile trout display parr marks, and some subspecies retain these marks into adulthood. Hatchery-reared trout are often identified by clipped adipose fins.

Rainbow trout spawn in early to late spring when water temperatures reach at least 6 to 7 °C. Females produce 2000 to 3000 eggs per kilogram of weight, depositing them in gravel redds. Eggs hatch in about four to seven weeks. Steelhead, the anadromous form, are iteroparous and may spawn multiple times, though fewer than 10 percent of native spawning adults survive from one spawning to another. Introduced populations in the Great Lakes have a survival rate as high as 70 percent.

Reader's Guide

The rainbow trout is significant both as a highly adaptable species for sport fishing and as a major invasive species. Its introductions to waters outside its native range—including the United States, Southern Europe, Australia, New Zealand, and South America—have damaged native fish through predation, competition, disease transmission, and hybridization. However, introductions into waters previously devoid of fish or with depleted stocks have created valuable sport fisheries, such as in the Great Lakes and Wyoming's Firehole River. The species' taxonomic history reflects evolving understanding of fish relationships, culminating in its reclassification from Salmo to Oncorhynchus in 1989. Some local populations, particularly of steelhead, are listed as threatened or endangered under the Endangered Species Act. The steelhead is the official state fish of Washington. The rainbow trout's global distribution and ecological impacts make it a key subject in conservation and fisheries management.

Did You Know?

• The rainbow trout is included in the list of the top 100 globally invasive species.
• The steelhead is the official state fish of Washington.
• The species was originally named by Johann Julius Walbaum in 1792 based on specimens from the Kamchatka Peninsula.
• Fewer than 10 percent of native steelhead adults survive from one spawning to another.