Kingdom   Animalia

Phylum     Chordata

Class        Actinopterygii

Order        Scombriformes

Family       Scombridae

Genus       Thunnus

Species     T. obesus

Bigeye Tuna Basics

The bigeye tuna (Thunnus obesus) belongs to the Scombridae family of tunas. Fishes live in tropical and temperate seas all around the world, and in many areas, they represent a valuable commercial fishery.

Bigeye Tuna Description

The shape of the bigeye tuna is rhomboidal, or football-shaped, like other tuna. At the tips of their conical heads, they have gigantic mouths, as well as big eyes on both sides. They have long pectoral fins, similar to albacore tuna. In adult animals, two dorsal fins as well as two anal fins are also present, as well as a set of around 5-8 fin lets between their tail fin and their anterior anal and dorsal fins on each of their dorsal and ventral sides. In adult animals, they’re completely yellow or orange.

The dorsal, or top side, of the bigeye tuna is charcoal, while the flanks and ventral, or bottom, have a silvery-white colour. Tuna are massive fish that may grow to be 8 feet long and weigh 400 pounds, placing them in the centre of the tuna family in terms of size, with the Atlantic bluefin tuna as the biggest.

Habitat and Distribution

Bigeye tuna may be found in tropical and temperate seas across the world’s oceans. However, they are not seen in the Mediterranean Sea.

Bigeye tuna are also epipelagic, as are various tuna species. They spend much of their time on the water surface, particularly during the night, when food is more abundant. During the day, they frequently plunge to depths of up to 1,500 feet beneath the surface. They generally gather with other fish of their particular species or with fish of comparable size, such as tuna.

Predators and Diet

The chase of prey is most likely the explanation for numerous tuna species’ deep diving habits. Bigeye tuna are quick, muscular swimmers that use their speed to attack a variety of foods, including fish and crabs. They are also known to hunt octopus, cuttlefish, and squid, among other cephalopods.

All but the greatest predators, such as the false killer whale and maybe orca, are capable of escaping predation by adult bigeye. Sharks, such as the mako shark and the great white shark, may also feast on them. Other big predatory fish species, including larger tuna, may be added to this list by juvenile tuna.

Reproduction

Bigeye tuna reproduce all year, but especially in the tropics. At higher latitudes, this pattern becomes more seasonal, maybe due to a more marked seasonal fluctuation in production in these areas.

Bigeye tuna are dispersed spawners, meaning that females discharge their eggs throughout the water stream, in which they are paired by sperm from males who perform the same. After external fertilisation, the embryo would develop into a larval fish that would join the zooplankton community. It will quickly mature into a small young tuna and start seeking smaller prey.

Bigeye tuna may live up to 16 years, with sexual maturation occurring between the ages of two and four.

Conservation Status

Bigeye tuna is a prominent commercial fishing target, with up to 500,000 tonnes taken each year throughout the world. Management of these species is challenging because of their migratory character, since they need the approval and collaboration of numerous countries. Because one of the ecosystem’s apex predators has been removed, this intensive fishing puts pressure on the population, with numerous negative consequences of lower trophic levels.

In addition to overfishing, the species faces danger from ocean warming caused by global climate change. The consequences of such changes are multifaceted and dynamic. One effect is a decrease or change in the marine phytoplankton population, which forms the foundation of the food chain upon which all other bigger creatures depend. Tuna and other species may face increased pressure when primary production declines, which, along with overfishing, might pose a threat to the species’ survival. The IUCN Red List of Threatened Species now lists the bigeye tuna as Vulnerable.

Fun Facts about the Bigeye Tuna!

Tuna are a fascinating and important fish species. They are not only important predators in their natural environments, but they are also important economically in fisheries all over the world. Despite being one of the lesser-known tuna species, the bigeye tuna is a powerful fighter. It is no less significant or intriguing, with a wealth of entertaining facts and insights to be discovered via its lens.

Uniquely Competent

Bigeye tuna, like other tuna species, are well-adapted to their habitats and possess distinct physiological characteristics that enable them to survive in each of their niches. The bigeye tuna is exceptionally well adapted to low-oxygen settings, with levels as low as 1.0 ml/L being tolerated. This is caused by the presence of a high quantity of haemoglobin in the blood, which allows it to bind to oxygen more quickly.

Because many deep, cold-water settings are oxygen-depleted, the bigeye tuna’s adaptation permits it to reach foraging places it wouldn’t otherwise be able to reach without its hemoglobin-rich blood.

Vertically Gifted

The physiological characteristics of the bigeye tuna are put to good advantage. Tunas have the most characteristic diurnal migratory behaviour pattern among tuna species, going into deep waters throughout the day and surface waters by night. During the day, they will often cruise to depths of up to 1,500 feet, experiencing a temperature differential of up to 20 °C from surface waters.

The average depth to which people dive varies throughout the globe, suggesting that they may be going for an ideal temperature range rather than a specific depth. They may have to dive deeper in hot tropical locations to attain these temperatures, but in colder temperate and subtropical seas, these temperatures will occur closer to the surface. Although tuna may not find it especially beneficial to live in cooler waters, they may complete this journey in reaction to their diet, which commonly includes copepods such as squid, which are well known for their own diurnal migratory.

Same Same but Different

Because they are so closely related, all tuna species share certain characteristics. As a result, it might be difficult to tell them apart. The example of the bigeye and yellowfin tuna is perhaps the finest illustration of this. Both develop to be around the same size: bigger than albacore tuna, but smaller than bluefin tuna. Both species have yellow fins and huge eyes. Both species are known in Hawaii as “Ahi,” the traditional term for tuna.

However, there are some significant distinctions between the two species upon closer observation. Bigeye tuna are more rotund, with a physique that is notably “plump.” When compared to yellowfin and other tuna species, it has especially big eyes and a huge skull. Although the yellowfin tuna is more well-known across the world, bigeye tuna flesh is favoured for sashimi due to its slightly greater fat content.

This example demonstrates how speciation isn’t always obvious. This is particularly true when organisms continue to adapt and develop in a changing and dynamic environment. Hybridization may be feasible in certain circumstances due to comparable qualities and overlapping surroundings, whereas in others, individuals of the same species may become geographically separated, ultimately resulting in two different species with similar characteristics and a recently shared ancestry.