Steelhead Trout


by Brendan Bane

Steelhead trout (Oncorhynchus mykiss) are famous fish. Their meat bears a mild, nutty flavor that has captured the attention of many cultures. They’re a popular choice for fish farming, and have thus been introduced into waters of every continent except Antarctica. But despite their wide range, scientists are concerned about conserving this species where it naturally occurs: on the Pacific Coast of North America.

As members of the Salmonid family, steelheads look similar to their salmon cousins. Their pelvic fins hang far back, toward the middle of the belly. Their faces share the same familiar frown, concealing a single row of sharp teeth. Bodies are sleek with round scales and dark speckling that terminates in a forked tail.

All steelheads spawn and hatch in freshwater streams. Sexually mature fish either settle in the stream in which they hatched and become the smaller, red-striped rainbow trout or venture into the ocean and become the larger (up to 55 pounds and 45 inches) silver steelhead trout. The two types are the same species, both of which always return to their birthing stream to spawn.

After finding the ideal stream conditions (not too turbulent, good gravel consistency), females nudge grooves into gravel beds to create nests, called redds, in which they lay clutches. Young trout emerge 3-4 weeks later, spend their juvenile years in the tributary, and choose between the two lifestyles later on.

In order to go from freshwater to the ocean (such fish are anadromous), steelhead bodies must tolerate varying degrees of salinity (fish who can do this are said to be euryhaline). Steelhead trout have adapted to withstand the change, but take time to acclimate when between environments.

In areas where they were introduced, like Southern Europe, South America, and Australia, steelhead trout thrive and outcompete native fish. But along the Pacific Coast, where they naturally occur, their numbers have declined for a number of reasons, ranging from dam construction to droughts (it’s difficult to pinpoint one factor when their life stages are so complex). Captive-rearing hatcheries, improved water quality and migration pathways have helped some populations to recover, while others remain at a low count.