Coho salmon, also known as silver salmon, feed on insects and plankton while they live in fresh water, then switch to a diet of small fish when they reach the ocean. When mature coho salmon return to fresh water, they rarely eat, because their energy is focused on spawning.
Coho salmon spend the first half of their life cycle in freshwater streams, rivers and lakes. Adolescent coho change as they prepare to migrate to the ocean: their backs darken, their bellies get lighter and their kidneys and gills begin to change in order to function in the saltwater habitat.
According to the National Oceanic and Atmospheric Administration, the average mature coho salmon is approximately 2 feet long and weighs close to 8 pounds, although they may weigh up to 35 pounds. Most coho live about three years before they return to their stream of origin, where they spawn once and die.
Anglers use spinners, plugs and lures that mimic small fish to catch coho salmon during the fall salmon runs. Another popular bait is roe, or fish eggs. The most successful fishermen adjust their fishing techniques and bait to match the natural eating habits of coho salmon through each stage of their migration, according to the Washington Department of Fish and Wildlife.