What does it mean if salmon are anadromous?

Anadromy is a term used to describe the life cycle of certain species of fish that are born in freshwater, migrate to the ocean to grow and mature, and then return to freshwater to spawn and die. Salmon are the most well-known anadromous fish. Other examples include steelhead trout, rainbow trout, and American shad.

Anadromous fish have evolved to take advantage of the different resources available in freshwater and the ocean. Freshwater rivers and streams provide a safe and protected environment for young fish to grow and develop. The ocean offers an abundant food supply that allows fish to grow to a larger size. Returning to freshwater to spawn allows fish to avoid predators and other hazards that may be present in the ocean.

The life cycle of an anadromous fish begins in freshwater. Fish are born in gravel nests that are constructed by their parents. The eggs hatch into fry, which begin to feed and grow in the river. As the fry grow larger, they move downstream to deeper and faster water.

After spending one to several years in freshwater, the fish smolt and migrate to the ocean. Smolt is the term used to describe young fish that are undergoing the physiological changes necessary for survival in saltwater. These changes include the development of a silvery skin, increased salinity tolerance, and the ability to osmoregulate (control the movement of water and solutes across their gills).

Once in the ocean, the fish spend several years growing and maturing. They feed on a variety of food, including plankton, small fish, and squid. Salmon can travel thousands of miles during their ocean migrations.

When the fish are ready to spawn, they return to the freshwater river or stream where they were born. The fish use their sense of smell to navigate back to their home river. The journey back to freshwater can be difficult and hazardous. The fish must swim against strong currents, leap over waterfalls, and avoid predators.

Once the fish reach their home river, they begin to spawn. The females dig gravel nests in the river bottom and lay their eggs. The males fertilize the eggs. The fish then guard the nest until the eggs hatch. After hatching, the fry remain in the river for a period of time before they migrate to the ocean.

The anadromous life cycle is a remarkable adaptation that allows fish to take advantage of the different resources available in freshwater and the ocean. This life cycle has also made anadromous fish a valuable resource for humans. Salmon and other anadromous fish are an important source of food for people around the world.