Coho

Coho, also known as silver salmon, popular game fish and one of five species of Pacific salmon. Like many other members of the trout and salmon family, coho are anadromous—they hatch in streams, where they spend one to two years before migrating to the Pacific Ocean. After roughly fifteen months at sea, coho travel several hundred miles back to their native streams, where they lay their eggs, or spawn, then die.

Historically, coho ranged along the coast of North America from Baja California north to Alaska and west across the Pacific to Korea. The species was successfully introduced in the Great Lakes of the United States, but attempts to introduce coho into the Eastern United States, Europe, Asia, and South America have been unsuccessful.

Mature coho average 61 cm (24 in) in length and weigh from 3 to 5 kg (7 to 11 lb). Coho weighing as much as 14 kg (31 lb) and measuring as long as 98 cm (39 in) have been recorded. At sea, the fish are a uniform silver color. As they approach freshwater to spawn, they turn a brownish red, sometimes almost black. Males develop a severely hooked jaw; the jaws of the females hook to a lesser extent.

While in streams and rivers, juvenile coho feed on insects, insect larvae, and small fish. In the ocean, adult coho feed almost exclusively on small saltwater fish. When they begin the long journey home to spawn, coho stop feeding entirely.

Coho arrive in their native streams to spawn in the autumn. Once on the spawning ground, males and females form pairs and the female uses her powerful tail to dig a nest, called a redd, in the gravel streambed. As she deposits her eggs in the redd, the male fertilizes them with milt (sperm). The female buries the fertilized eggs with gravel and guards the nest until she dies, usually about two weeks later. The eggs hatch the following spring.

Like the other Pacific salmon, wild populations of coho are in decline, and some populations have been declared extinct. Coho spawning habitat is destroyed by human development, and their migration can be blocked or impeded by dams. Dams also threaten coho survival by storing water in reservoirs, sometimes drying up or flooding the small creeks where juveniles live. Very few truly wild populations exist because most populations have been extensively supplemented with fish produced in hatcheries.

Scientific classification: The coho salmon is a member of the family Salmonidae in the Salmoniformes order. It is classified as Oncorhynchus kisutch.