Rainbow Trout

The rainbow trout, redband trout, or steelhead (Oncorhynchus mykiss) is a species of trout native to the Pacific Ocean and in North American rivers and lakes west of the Rocky Mountains. It also is native to parts of East Asia. Rainbow trout are now worldwide in distribution and are a highly prized game fish. They have been introduced to at least 45 countries, and every continent except Antarctica. However, in some of these locations, such as Australia, they have had very serious negative impacts on upland native fish species.

Rainbow trout are unusual in that although they can spend their entire life in fresh water, they are capable of migrating to sea water when conditions are right, though they must return to fresh water to breed. The freshwater form is usually called "rainbow trout" or "redband trout", while the marine form is often called "steelhead", but these populations belong to the same species.

S. fontinalis prefers cool, clear waters in lakes, rivers, and streams, being sensitive to poor oxygenation. Its diverse diet includes crustaceans, frogs and other amphibians, insects, molluscs, smaller fish, and even small aquatic mammals such as voles. It provides food for seabirds and suffers attack by lampreys.

The species normally spends its entire life in fresh water, but some individuals-colloquially called "salters" or "sea run"-spend up to three months at sea in the spring, remaining within a few kilometres of river mouths. The fish return upstream to spawn in the late summer or autumn. The female constructs a depression in a location in the stream bed where groundwater percolates upward through the gravel. One or more males approaches the female, fertilising the eggs as the female expresses them. The eggs are slightly more dense than water. The female then buries the eggs in a small gravel mound. The eggs hatch in approximately 100 days.

Rainbow trout are the smaller variety, found only in fresh water. Steelhead spend their adult lives in the ocean, but return to spawn in the streams in which they were born. They occur in cool streams up to 4,500 m in elevation. Rainbows and steelhead have small black spots along their back, dorsal fin and caudal fin. Rainbows have a pink streak that runs from the gill cover to the caudal fin. The color of a rainbow's back varies from blue or green to a yellow-green or brown. Steelhead usually lack the pink stripe, except when young or spawning, and have chrome-colored sides. Rainbows are distinguished from their cousins, the cutthroat trout (Oncorhynchus clarki) by their short maxilla, which reaches to, but not past the rear margin of the eye. Rainbow trout also lack hyoid teeth, a feature present in cutthroat trout.

Rainbows range from 30 to 45 cm (12 to 18 inches) in length. Steelheads grow longer, ranging from 50 to 100 cm (20 to 40 inches) in length. Steelhead range in weight from 2.5 kg to 10 kg.

Rainbow trout is popular in Western cuisine and is often farmed for food. It has tender flesh and a mild, somewhat nutty flavor. However, farmed trout and those taken from certain lakes have a pronounced muddy flavor which many people find unappealing; many shoppers therefore make it a point to ascertain the source of the fish before buying.