Tuna

Beloved by millions of people as a culinary delight for its rich, succulent taste, the mighty tuna fish roams the world’s oceans. Its sleek, streamlined torpedo-shaped body makes it one of the fastest fish in the world and a rather capable predator. Tuna fish is also a critical part of the world’s food supply, which has made it susceptible to overfishing.

3 Incredible Tuna Facts

• The tuna fish is a migratory species that has no established home range. Some species travel thousands of miles per year.
• The tuna fish has a vast network of blood vessels in its body that always keeps the body temperature above the temperature of the surrounding water.
• The fish can swim at speeds of more than 40 mph.

Classification and Scientific Name

Tuna are ray-finned saltwater fish belonging to the tribe Thunnini, a subgroup of the mackerel family Scombridae. They are classified under the class Actinopterygii. The word “Thunnini” seems to derive from the Ancient Greek word for tunny fish, which in turn means to run or dart along.

There are some 15 species of Thunnini in the world. Most of these species belong to the genus Thunnus, the “true tuna.” The skipjack belongs to its own genus, Katsuwonus. Here are a few of the most well-known of these fish:

• Skipjack Tuna (Katsuwonus pelamis): Although the skipjack isn’t among the true tuna species, it nevertheless has many of the hallmarks of these fish, including the same body shape, color, and appearance. As the smallest of the commercially fished species, it actually makes up much of the worldwide tuna catch.
• Yellowfin Tuna (Thunnus albacares): As the name implies, this species has yellow fins, including a set of particularly long dorsal and anal fins that curve back almost to the tail.
• Bluefin Tuna (Thunnus thynnus): The largest species by size, the bluefin is divided into a few different species, including the southern bluefin, Pacific bluefin, and Atlantic bluefin.
• Albacore Tuna (Thunnus alalunga): Slightly larger than the skipjack, the albacore has very long pectoral side fins that reach almost the entire length of the body.

Evolution and Origins

The bluefin tuna came from an ancestor that produced heat externally. The oldest known fossils of tuna were discovered in the Tethys Sea deposits from the Middle East, southern Europe, and the London clay formation.

These fossils are from the late Paleocene (55 to 65 million years ago) or Early Eocene (50 to 55 million years ago) periods of the Tertiary era.

The western population of Atlantic bluefin tuna spawns in the Gulf of Mexico, while the eastern population spawns in the Mediterranean Sea.

These tunas used to be found throughout the Atlantic Ocean, but now they are mostly found in the North Atlantic Ocean and associated seas, including the Mediterranean Sea.

Appearance

A true spectacle in the water, this is one of the largest fish in the world. The bluefin can grow up to an enormous 2,000 pounds (the world record for a caught fish is 1,500), but realistically, most species almost never grow larger than 500 pounds.

The fish is characterized by a long, torpedo-shaped body tapering off to a forked or crescent tail. Most of the body is covered in smooth, shiny blue or silver metallic skin with scales adorning only certain segments. It also has small “finlets”, leading up to the tail, that look like little spikes.

Distribution, Population, and Habitat

These fish show a preference for tropical and temperate waters all over the Atlantic, Pacific, and Indian Oceans. It occupies the pelagic zone, meaning all open oceans besides the coastline and the bottom layer.

Although exact population numbers are not known, the oceans teem with millions of these fish. The annual catch is carefully managed by conservation organizations to prevent overfishing, but because of its migratory nature, this requires international cooperation.

Predators and Prey

These fish are among the top predators in the ecosystem. It keeps prey populations in check while providing an abundant meal for the few predators that do feed on it.

What does the tuna eat?

These fish feed on all manner of shellfish, squid, and many species of perciform fish. Juvenile fish also consume plankton during the first crucial stage of life.

What eats the tuna?

Due to its size, only the largest predators feed on adult fish, including some species of sharks and whales. Seabirds and other fish species also consume the juveniles.

Reproduction and Lifespan

These fish are prolific breeders that can produce millions of eggs per year. Fertilized right in the water column of the open ocean, the eggs hatch after only a few days, although actual development to adulthood can take years. Tuna is relatively long-lived for a fish. While the yellowfin tuna only lives about seven years, some bluefin species can live up to 40 years in the wild.

Fishing and Cooking

These fish are a cornerstone of many people’s diets and one of the most popular commercial and recreational fish in the world. Some 4.9 million tons of tuna were caught in 2016, most of which were skipjack.

This heavy reliance has led to plenty of over-exploitation. According to the International Seafood Sustainability Foundation, 13% of all tuna stocks are overfished worldwide.

Unlike the white meat of most fish, tuna has pink or dark red flesh thanks to the abundant quantity of oxygen-rich blood. Most of this tuna is canned light meat, but the higher quality meat can be served as sushi, sashimi, steaks, or any other fish recipe.

It’s also popular in sandwiches, salads, wraps, and grilled dishes. Regardless of the recipe, this fish is abundant in nutrients such as vitamins and good fats.