Tuna

Tuna are highly specialized saltwater fish belonging to the tribe Thunnini. This tribe is a subgroup of the Scombridae family, which also includes mackerels.

These fish are vital to ocean ecosystems and global food supplies. They are known for being active, agile predators in the open ocean. Their streamlined bodies allow them to be among the fastest pelagic fish. Pelagic refers to animals that live in the open sea, away from the shore.

Because of their speed and size, they are important to both commercial fishing and recreational sport fishing.

The anatomy of a tuna is perfectly designed for high-speed movement. They possess a sleek, elongated, and streamlined body shape. On their backs, they have two dorsal fins that are closely spaced but separate. The first dorsal fin is depressible, meaning it can be laid down flush into a groove. This feature reduces drag when the fish is swimming at high speeds. They also have seven to ten yellow finlets running toward the tail. The tail itself is lunate, which means it is shaped like a crescent moon.

To help with camouflage, tuna use countershading. Their dorsal side is a dark metallic blue, while their ventral side is silvery. This makes them harder to see from both above and below in deep water.

One of the most remarkable aspects of tuna biology is their ability to maintain body temperature. Most fish are ectothermic, meaning their temperature matches the surrounding water. However, tuna, along with opah and mackerel sharks, can maintain higher temperatures. They achieve this through a process called endothermy. They use a specialized system called the rete mirabile, or "wonderful net."

This is an intertwining of veins and arteries that acts as a counter-current exchange system. It reclaims metabolic heat from venous blood and transfers it to arterial blood. This allows them to keep their brain, eyes, and skeletal muscles warm. This warmth supports faster swimming and lets them survive in much cooler waters.

Tuna muscle tissue is also unique compared to many other fish. While most fish have white flesh, tuna muscle ranges from pink to dark red. This color comes from high concentrations of myoglobin. Myoglobin is an oxygen-binding molecule that helps deliver oxygen to the muscles. This high oxygen capacity fuels their powerful, aerobic swimming style. However, very fast swimming can cause cavitation. Cavitation occurs when collapsing bubbles create a vapor film around the fins. This film can actually limit the maximum speed a tuna can achieve. While they do not feel the bubbles like dolphins do, cavitation can cause physical lesions on their fins.

The Thunnini tribe is a monophyletic clade containing 15 different species. These species are spread across five different genera. The genus Thunnus contains the "true" tunas, which include both bluefin and yellowfin groups. For a long time, scientists thought Atlantic and Pacific bluefin were the same species. However, in 1999, researcher Collette proved they are distinct species using molecular and morphological evidence. Other genera in the tribe include Allothunnus, Auxis, Euthynnus, and Katsuwonus. These include slender tunas, frigate tunas, little tunas, and skipjack tunas.

Historically, the name "tuna" has deep linguistic roots. It comes from the Spanish word "atún," which originated from Andalusian Arabic. This traces back even further to the Middle Latin term "thunnus." The Ancient Greek word "thýnnos" was used specifically for the Atlantic bluefin. This Greek name is derived from "thýnō," which means "to rush" or "to dart along." This name perfectly describes the animal's rapid movement through the water. In some English contexts, they have also been called "tunny" or even "Chicken of the Sea."

Tuna are a massive part of the global fishing industry. In 2007, annual catches reached more than 4 million tons. The Pacific Ocean provides about 68 percent of this total catch.

Different methods are used to catch them, such as purse-seining, longlining, and pole and line. Purse-seining is the most common, accounting for 62 percent of production. Some tuna are incredibly valuable; in 2019, a single bluefin sold for 333.6 million Japanese yen. This is approximately 3.1 million US dollars.

However, overfishing is a serious concern. Species like the southern bluefin tuna are threatened with extinction due to high demand. This makes sustainable fishing practices essential for the future of the species.