MigrationsA number of species of fish, including shad and salmon, migrate from the sea to fresh water in order to spawn. Others, such as eels, migrate from fresh water to spawn in the sea. Cod, herring, and a number of other species move southward in winter and northward in summer. Many other species migrate from shallow water in summer to deep water in winter. Some of these migrations are made in search of food, others in order to spawn.
Probably the most remarkable of all fish migrations is that of the European eel, which travels about 3,000 miles (4,800 km) to spawn in the Sargasso Sea in the North Atlantic. The eel larvae travel an equal distance to reach Europe. They accomplish the journey in about three years.
Salmon have been caught nearly 2,000 miles (3,200 km) from the rivers from which they entered the sea. The bluefin tuna probably travels farther than any other fish. It is believed to travel constantly throughout its life, seeking warm regions in winter and cool areas in summer.