The oxygen and nutrient uptake in the circulatory system is transported to these swimming muscles rather than to tissues required to pump water over the gills in other teleost fish.

Furthermore, their large hearts, with a characteristic organization of muscle fibres, allow for comparatively high cardiac outputs, as well as rapid ejection of stroke volume.

This, together with the organization of blood vessels and a countercurrent heat exchange system, allows the southern bluefin tuna to rapidly deliver oxygen to tissue, while preserving energy necessary for their active lifestyle.

Southern bluefin tuna, along with other marine teleost fish, have acquired a variety of proteins and mechanisms which allow the secretion of ions through the gill epithelium.

[6] Due to the southern bluefin tuna's high metabolic need, ions must be taken up relatively quickly to ensure sufficient concentrations for cellular function.

[15] The intake of sodium and chloride, along with lower relative concentrations of potassium and calcium ions in the seawater allow southern bluefin tuna to generate the action potentials required for muscle contraction.

[17] The gills, due to their large surface area, play a significant role toward osmoregulation in the tuna to maintaining water and ionic balance by excreting NaCl.

[21] Southern bluefin tunas are thermo-conserving and can function over a wide range of temperature conditions, which allows them to dive from the surface of the water to depths of 1,000 m (3,300 ft), in only a few minutes.

Some have hypothesized that they take refuge in warmer areas of water fronts and eddies after these foraging periods, but others suggest that these migrations are only associated with the aggregation of prey.

[31] In bluefin tuna, large lateral cutaneous vessels that branch off into the arteries and veins of rete mirabile supply blood to the red muscle, instead of a centrally located aorta.

Due to their anatomical positioning, the heart and the liver are the coldest organs and significant work needs to be expended for them to serve a regionally warmer body.

The carotid rete has been observed to have strong insulation properties, allowing blood to travel a great distance throughout the body while reducing the amount of heat lost to surrounding tissues prior to the brain and eyes.

The elevated temperatures in the brain and eyes allow the southern bluefin tuna to search for food more effectively by reducing reaction time and creating stronger vision.

[36] One of the adaptations that allow bluefin tunas to have large migratory patterns is their endothermic nature, whereby they conserve heat in their blood and prevent its loss to the environment.

[39] This allows the fish to maintain a high rate of oxygen consumption as it continually swims out to others areas of oceans in search of food and ground for growth and reproduction.

The onset of industrial fishing in the 1950s, in conjunction with ever-improving technologies, such as GPS, fishfinders, satellite imagery, etc., and the knowledge of migration routes, has led to the exploitation of southern bluefin tuna across its entire range.

[citation needed] In 1994, the Convention for the Conservation of Southern Bluefin Tuna formalised existing voluntary management measures between Australia, New Zealand and Japan.

[42] After the quota reduction, Australia had the highest "effective catch limit" with 4,015 tonnes, followed by Japan (2,261), Republic of Korea (859), Fishing Entity of Taiwan (859), New Zealand (709), and Indonesia (651).

Juvenile tuna are mainly caught on the continental shelf in the Great Australian Bight region from December to around April each year, and weigh on average 15 kg (33 lb).

Around April, harvest begins and fish are gently guided into a boat (any bruising lowers the price) where they are killed, flash frozen and most placed on Tokyo-bound planes.

Southern bluefin tuna are largely fed fresh or frozen small pelagic fishes (including Sardinops sagax) and the use of formulated pellets is not yet viable.

[77] The state-of-the-art Arno Bay hatchery was purchased in 2000, and undertook a $2.5 million upgrade, where initial broodstock facilities catered for kingfish (Seriola lalandi) and mulloway (Argyrosomus japonicas), along with a live-feed production plant.

Clean Seas will maintain its broodstock to enable discrete research in the future, however they do not expect commercial production to be achieved over the short to medium term.

Recreational fishing targeting southern bluefin tuna is permitted in all states and territories and is regulated by various combinations of bag, boat and possession limits.

Clean Seas has attempted to address this by focusing research effort on closing the life-cycle of the species with the potential benefit of alleviating some of the fishing pressure on declining stocks, but has not succeeded.

Industry spokesperson Brian Jeffriess said of the certification: "This is one of the few awards to actually cover both the wild fish catching and the whole farming supply chain and within that labour standards, crew safety, traceability, carbon footprint... every conceivable sustainability test.

Toxicants, such as mercury and PCBs (polychlorinated biphenyls), can build up over time, particularly through the tuna feed, with some evidence of contaminants being more elevated in farmed fish than in wild stocks.

[96] According to the South Australian Sardine Industry Association, 94% of its annual catch is utilized as feedstock for farmed SBT, with the remainder used for human consumption, recreational fishing bait and premium pet food.

[97] Fishing effort is largely concentrated in southern Spencer Gulf and Investigator Strait near Kangaroo Island in South Australian state waters.

In 2005, the potential impact of this fishery upon colonies of little penguins was considered a future research priority, due to the relative paucity of alternative prey species.