Facts: The Tuna

The tuna is a streamlined fish built for speed. There are currently 15 species. They are found worldwide except in polar seas. They inhabit the upper and middle layers of the ocean. Tuna are obligate ram ventilators. This means that they need to swim constantly to make water pass through their gills. Since they must constantly swim to oxygenate their blood, their muscular metabolism continuously generates heat. This gives them a unique advantage because they are able to regulate their body temperatures. This enables them to tolerate a wide range of water temperatures. The back of a tuna has two dorsal fins. The first can be flattened. Small finlets run from the dorsal fin to the tail. They are highly migratory. They migrate on a yearly cycle between feeding and spawning areas. They normally travel in small schools. The schools may contain several different species of tuna. Very large tuna, over 500 lbs, are normally solitary. They often feed on small, schooling fish such as herring and mackerel. They may also feed on squid and crustaceans. Tuna vary greatly in size. Some, like the skipjack and blackfin, rarely exceed 3 ft, while the Atlantic bluefin tuna can grow over 10 ft long. Tuna typically reach maturity between 3 and 5 years of age. Large females may release millions of eggs per spawning season. Tuna grow rapidly and live long. Bluefin tuna are thought to live more than 30 years. Many of the tuna species are important commercial food sources with high economic value. They are marketed fresh, frozen, and canned. In Japan, a large bluefin tuna once sold for over $3 million. Sport fishing for tuna is also popular. Because of their high demand, many tuna stocks are highly exploited, overfished, or depleted. The Atlantic bluefin tuna is endangered. The southern bluefin tuna is critically endangered. Tuna schools often associate themselves with dolphins. Before efforts for dolphin-safe tuna, it used to be very popular for commercial fishing vessels to search for dolphin pods and encircle the pods with nets to catch the tuna below them. For more marine facts, click the SUBSCRIBE button!!