Fish that are high in omega-3 fatty acids are fatty, coldwater fish such as salmon, tuna, black cod, tilefish, halibut, swordfish, mackerel, anchovies, sardines, trout and herring. Omega-3 fatty acids are polyunsaturated fats that can help prevent cardiovascular disease and reduce the risk of other diseases.
Many kinds of salmon and trout spend their lives both in the ocean and fresh water. They are born in the freshwater streams that their parents were born in and return to the ocean after they've reached a certain size. They then come back to the stream to spawn. Most types of salmon die after they spawn.
Atlantic herring are always found in the ocean and congregate in enormous schools. The herring is a small, silver-colored fish with a green or blue-green back. Though it eats zooplankton, which are tiny animals that drift along with the ocean currents, the herring is food for many predators including seals, whales, bigger fish and humans.
The bluefin tuna is a distinctive fish, largely because it's warm-blooded. It's also one of the fastest and largest fish in the ocean and can reach weights of up to 1,000 pounds. To increase its speed, the dorsal and pectoral fins retract into slots on the fish's body to reduce drag.