YELLOWFIN TUNA: CHARACTERISTICS, HABITAT, FEEDING - BIOLOGY - 2025

The yellowfin tuna (Thunnus albacares) is a fish belonging to the family Scombridae. Its body is spindle-shaped and elongated, covered with small scales. It has two dorsal fins and one anal fin, which can measure up to 20% of the furcal length. Its pectoral fin is medium in size.

Regarding the coloration, the dorsal region is metallic bluish black, contrasting with a silvery-gray belly. The first dorsal fin is bright yellow, while the second dorsal and anal fin are lighter yellow.

Yellowfin tuna. Source: Almcglashan

The pinules are bright yellow, with fine black edges. The ventral region is characterized by the presence of more than 10 dark vertical stripes. When the yellowfin tuna is adult, these lines tend to disappear.

Yellowfin tuna or albacore, as this species is also known, is an epi and mesopelagic animal. It is found distributed in the open waters of the subtropical and tropical regions of the oceans worldwide, except in the Mediterranean Sea.

The Thunnus albacares is a highly migratory fish, which travels long distances in search of its prey and to find warm waters where the female can spawn.

characteristics

Thunnus albacares drawing

Body

Yellowfin tuna have a fusiform body, with a more stylized shape than other tunas. Below the first dorsal fin it is deeper, while towards the caudal peduncle it narrows. At the lateral level, it is slightly compressed on the body.

Its head is conical and the eyes are small. In the first gill arch it has 26 to 35 gill rakers.

This fish has a swim bladder. This flexible fabric bag controls the buoyancy of the tuna in the water, without the need for it to make a great muscular effort to achieve it. As for the vertebrae, it has 18 pre-caudal and 21-caudal.

On the other hand, it differs from the rest of the tunas by the characteristics of its liver. In Thunnus albacares, this organ is smooth and the right lobe is larger than the other two. In contrast, T. obesus and T. thynnus have a striated liver with the three lobes of equal proportions.

Fins

Thunnus albacares

Yellowfin tuna have two dorsal fins, separated by a narrow gap. In the adult, the second dorsal fin is long, and in large species they are relatively longer.

The first dorsal fin has 11-14 hard rays, while the second has 12-16 soft rays, followed by approximately 10 pinnules. As for the anal fin, it is long and has between 11 and 16 rays.

The pectoral fin is also large, reaching beyond the space between the dorsal fins. It has 30 to 36 soft rays. In relation to the caudal peduncle, it is thin and includes 3 sets of keels.

This species has between 7 and 10 ventral and dorsal finlets. In addition, it has two small inter-pelvic protrusions.

Coloration

Thunnus albacares has a dark metallic blue or greenish dorsal area. This shade fades to the sides, ending in a silvery white belly. In this area there are about 20 discontinuous vertical lines, alternated with some points.

A distinctive aspect of this tuna is the golden and blue stripes that run along the entire side. In relation to the fins, the second dorsal and the anal have a bright yellow tone, which stand out on the dark body.

Size

Yellowfin tuna is a large species, within the Thunnus genus group. Their body can be between 240 and 280 centimeters long, with a weight that can reach 200 kilograms.

Taxonomy and subspecies

-Animal Kingdom.

-Subreino: Bilateria.

-Filum: Chordata.

-Subfilum: Vertebrata.

-Infrafilum: Gnathostomata

-Superclass: Actinopterygii.

-Class: Teleostei.

-Superorden: Acanthopterygii.

-Order: Perciformes.

-Suborder: Scombroidei.

-Family: Scombridae.

-Subfamily: Scombrinae.

-Tribe: Thunnini.

-Gender: Thunnus.

-Species: Thunnus albacares.

Habitat and distribution

Yellowfin Tuna (Thunnus albacares) in the Gulf Stream

Yellowfin tuna is found in all subtropical and tropical waters worldwide, except in the Mediterranean Sea. Its habitat ranges from latitude 40 ° N to 35 ° S. Regarding the thermal limits, it is located in waters between 18 and 31 ° C.

Habitat

The vertical distribution in the sea could be influenced by the thermal characteristics of the water column. Generally, yellowfin tuna are limited to the first 100 meters below the sea surface, being able to swim up to 200 or 400 meters deep.

This could be related to oxygen, since concentrations below 2 ml / l, which can be found below the thermocline, are not the most favorable for the development of this fish.

Thus, this pelagic species prefers the mixed layer that is found above the thermocline and, physiologically, it could be restricted from living in temperatures below 8 ° C.

However, despite this, recent research indicates that yellowfin tuna, while submerged, occupies 8.3% of the time making deep dives at 578, 982 and 1160 meters. In relation to the registered temperatures, they were 8.6, 7.4 and 5.8 ° C respectively.

Said temperatures and depths exceed those previously reported. This could be an indication that Thunnus albacares has the physiological capacity and behavior to dive deep and cold areas of the ocean.

Migrations

This fish performs migrations, traveling long distances at high speed. These mobilizations are associated with reproduction and the search for prey to feed. They generally travel in groups, which are not necessarily made up of members of the same species.

This migratory behavior can vary according to age. Thus, juveniles tend to stay close to coastal areas, while pre-adults migrate to higher latitudes. As for adults, they can move both at high latitudes, in the summer, and across the ocean.

According to research, the Thunnus albacares carries out transatlantic migrations. However, in the Pacific Ocean, there is little evidence of long-range movements, such as from south to north to south or from west to east.

This could suggest little genetic exchange between the eastern, western and central Pacific Ocean populations. As a consequence, some subspecies of yellowtail tuna could probably develop.

Variations related to habitat

The longevity of this species varies according to the region it inhabits. Thus, in the Indian Ocean, this fish can live up to 7 years. As for the eastern Pacific, longevity is 4.8 years and in the western Pacific it is approximately 6.5 years. Those who live in the Atlantic live about 8 years.

State of conservation

Yellowfin tuna populations have declined, due, among other factors, to their disproportionate exploitation. Due to this situation, the IUCN has categorized it within the group of species that, if the pertinent conservationist actions are not taken, could be vulnerable to extinction.

Threats

Thunnus albacares is a very popular species for its meat. In more than 35 countries, the commercial fishery is directed almost exclusively at catching this fish. The main countries where yellowfin tuna is hunted are Japan, Mexico and the United States.

As for the methods to catch them, there is purse seine fishing, pole fishing and longline fishing. Experts have conducted research to find out the status of this fish in the Pacific, Indian and Atlantic oceans.

The results show that yellowfin tuna is widely exploited in all oceans, with the exception of the Indian Ocean, where it is caught in moderation. Another factor that could affect the populations of yellowfin tuna in the very near future is the acidification of the Pacific Ocean.

This variation in the pH of ocean water can cause multiple damage to the organs of the larvae of this fish. According to research, injuries occur in muscle tissue, kidney, liver, pancreas, and eyes. In this way, their development is altered, thus drastically reducing their survival rate.

Conservation actions

One of the actions to preserve yellowfin tuna is related to the temporary closure of its hunt. In this sense, Mexico, in a joint effort with the Inter-American Tropical Tuna Commission, proposes the closure of this activity for three months.

The intention is to reduce fishing, allowing the population to recover reproductively. For example, in 2009 in the western Pacific there was a two-month closure of fishing and in 2010 it was carried out for three months.

Reproduction

Yellowfin tuna are apt to start breeding between two and three years. However, the size of the fish that is sexually mature can vary depending on the region where it lives.

Thus, in the eastern Atlantic, females have a predorsal length of 32 centimeters and a furcal length of 108.6 centimeters. In contrast, in the western Pacific, most females have a furcal length of 92 centimeters.

Reproduction occurs during any time of the year. However, during the summer it is usually the maximum mating peak. On the other hand, experts point out that the minimum water temperature for spawning is 26 ° C.

This is why the Thunnus albacares travel long distances, in search of warm subtropical and tropical regions to mate. In this sense, in the tropical waters of Central America and Mexico this fish could spawn at least twice a year.

The female expels millions of eggs, which are fertilized by the sperm that the male releases into the waters of the open sea. Of the total number of embryos, few reach adulthood, because a large part are consumed by predators.

Eggs and larvae

The eggs are pelagic, transparent, spherical and floating. Regarding size, the diameter of the oocyte is 0.90 to 1.04 millimeters. These do not present a fat globule and their incubation lasts between 24 and 38 hours.

In relation to the larvae, they are pelagic and have a total length of 2.7 millimeters. These are characterized by having 39 vertebrae, the first dorsal fin is pigmented and the tail lacks color. Also, the chin has a black spot.

The pigmentation patterns of the species are developed in the larvae around two and a half days after laying. The duration of the larval stage is 25 days.

After 25 days, the larvae give way to juvenile tunas. These grow quickly. At 18 months they weigh 3.4 kilograms and at 4 years, their body mass is 63.5 kilograms.

Feeding

The Thunnus albacares is an opportunistic predator. The main prey include fish, crustaceans, and cephalopods. Thus, they feed on sardines, flying fish, anchovies, mackerel and other tunas. Also, they eat squid, cuttlefish, octopus, crab, shrimp, and lobster.

Its diet may vary according to the seasons and the area it occupies. For example, in southern Brazil, during the winter, this fish feeds on teleost fish and squid (Ornithoteuthis antillarum). In the spring, yellowfin tuna mainly consume Phrosina semilunata and Brachyscelus crusculum.

The age of the fish also influences its diet. Thus, while the adults living in the eastern Atlantic eat Cubiceps pauciradiatus in large proportions, the young hunt other species.

Juvenile Thunnus albacares generally remains stable between 30 and 90 meters deep, making few vertical migrations. This makes them predators of small mesopelagic fish, such as Vinciguerria nimbaria.

To capture their prey, yellowfin tuna mainly use their sight, as they usually hunt them during the day, in surface waters. In addition, this fish can swim agilely and at high speeds, reaching between 50 and 80 km / h. Thus, it can go after its prey and capture it with ease.

Behavior

Yellowfin tuna, like other tunas, is a gregarious fish that generally forms schools. These can be free or associated with floating objects, with fish of the same species or of different species.

The conformation of the shoal may vary according to age. Thus, adults are usually grouped with fish of a similar size to this one.

In relation to free banks, where the animal is not associated, they are generally monospecific and are made up of large animals. However, in some cases there may be mixed groups, made up of other species of tunas.

In the eastern Atlantic, Thunnus albacares is frequently associated with various floating objects, such as dead cetaceans, live animals or seamounts. The school associated with objects is made up of small fish, less than 5 kilograms.

In this way, yellowfin tunas can concentrate at night under the object and during the day, they form free schools, to swim and capture the prey. The associated groups are usually multispecific, so the tuna could share with other species such as cetaceans, turtles and some shark species.

References

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