Tuna fish have been some of the worldâ€™s most abundant and physiologically advanced fish in the world. They have inhabited the world's oceans since the Mesozoic era, which was approximately 60-70 million years ago. In this paper we will discuss the different and most common types of tuna along with fishing and other information.
The first type of tuna is called Euthynnus alleteraturs (little tunny). These are the smallest fish in all the tuna family. They are described as steel blue with a primarily silver belly. They usually have several wavy lines above the lateral line. The lateral line is the horizontal line that runs across the middle of all fish. Little tunny also are covered with black spots located below the pectoral fin(see graph A). They are found throughout the Atlantic Ocean along with most tropical and subtropical areas, also found in the Mediterranean, black, and Caribbean seas. They migrate enormous distances. They eat most crustaceans and squids. They average in weight is between six and ten pounds, however some have been recorded at thirty pounds (insert).
The second types of tuna are called Katsuwonus pelamis (oceanic bonito, or slipjack tuna). These fish are describes as having a dark purple back and a silver underside. They are striped horizontally with three to six dark lines. These fish live in warm water throughout the world(see graph B). They tend to build in large schools. They feed on primarily cephalopods and mollusks and cannibalism is fairly common in this species. Oceanic bonito's most common predators are whales and sharks. Bonito and slipjack are found in sub tropical to sub tropical waters all around the globe.
The next type of tuna is Thunnus alalunga(pacific albacore), These fish are simply put built for speed. There bodies are in the shape of a torpedo, with a powerful concave shaped caudal fin. This allows this fish to reach speeds of over 50 miles and hour (80 kilometers). Like their cousins they have a dark purple area above the fishes lateral line, with a light silvery colored underbelly. They have extremely elongated pectoral fins; they extend to over half the length of their bodies. Because of the length of their pectoral fins they are commonly referred to as "longtail tuna"(Insert). These fish are used in most cans of tuna. They are highly migratory species that are found in sub tropical to temperate waters.
The fourth type of tuna is the Thunnus thynnus, or the bluefin tuna. Bluefin tuna are some of the biggest boniest fish in the world's ocean. They have been weighed at over 1,200 pounds, and over 10 feet in length. Like their name these tuna are a brilliant blue color on the back, and turning silver on their bellies. Unlike thier cousins bonito they lack the black markings that helps people easily distinguish them. These tuna, like it's cousins, are built for speed, which makes them a favorite target for anglers. Bluefin tuna are found in temperate water in the north Atlantic and Pacific. Their meat is some of the best in the tuna family and is often found in sushi shops.
The last type of tuna is called the yellowfin tuna. This fish is said to be one of the most brilliantly colored fish in the world's oceans. It is yellow on it's back with silver on it's underside. In Hawaii they are called ahi by local fisherman, which mean fire in the Hawaiian language. Yellowfins have been weighed in at as much as 450 pounds. And pound for pound are considered the strongest fish in the world. The yellowfins are found in most tropical water and some times even into sub-tropical waters. Hawaiians fish the yellowfin year round.
Members of the tuna family live in nearly all of the world's oceans. Tuna are highly migratory animals, which often migrate in huge schools. Tuna have been recorded swimming alongside large schools of dolphins. Scientists have hypothesized that this occurs because dolphins and tuna hunt the same huge schools of squid, however the dolphins have more sophisticated ways of finding these sporadic schools. So the larger members of the tuna family are often observed swimming in the same schools as dolphins. During spawning season a male and female will leave the school and release sperm and eggs into the water. They mix and then it will float to the surface where they will hatch in around thirty hours. The female will release anywhere from one to a couple million eggs into the water. The larvae then feed of the yolk in the egg until it's digestive track can become fully developed. These larvae are favorite feasts of other fish and birds, which make mortality rates fairly high. If the larvae survive past the few weeks then its chance of making to adulthood are much better.
Tuna have developed a variety of physiological characteristics that allow them to be extremely mobile and have extremely high endurance. These fish have adapted an interesting way of breathing. They swim with their mouths open which forces oxygen over their gills. They are able to regulate their body temperatures and ultimately their muscle through an elaborate circulatory system. This circulatory system, which has a system of countercurrent heat exchange systems that reduce the amount of heat that the tuna looses during respiration (Insert). This ultimately means that often the body temperature of the certain types of tuna is higher then it's surrounding water temperature. Tuna have very high metabolism rates that help there muscle exchange oxygen. Tuna must eat high amounts of food to sustain their metabolism rates. They must consume 25% of their body weight in food each day. All these very highly evolved characteristics enable tuna to be one of the quickest fish in the ocean. Their design it by flawless, simply put a miracle of Mother Nature.
Tuna is the backbone of most canneries in both Europe and North America. The Greeks are said to have hunted tuna. Most tuna caught commercially are caught in huge dragnets sometimes miles long. However these nets have been highly controversial because often times dolphins, whales, and seals get entangled and die of suffocation. Many marine biologists contribute this massive worldwide commercial fishing to decline populations of dolphins, whales, and seals. Some new techniques have been invented though. The Japanese have invented a way of fishing called longline fishing. Boats set up a line supported by small flotation devices, attached is a set of lines and baited hooks. The bait is what attracts the fish to the hooks and line. After the line is full of desirable fish then it is pulled back in. The lines can extend for miles and miles making them very valuable and environmentally friendly.
Tuna are some of the most philological advanced fish in the world's ocean. We must protect the numbers in which we purge the ocean. Otherwise these amazing fish will be eliminated from our oceans.