Tuna: A Complete Guide to the Popular Saltwater Fish

Tuna are large, fast swimming fish that are highly sought after for commercial and recreational fishing worldwide. They belong to the genus Thunnus and family Scombridae. There are 15 known tuna species across 5 genera. Tuna are an important food source, with commercial tuna fishing bringing in over 4 million tons per year globally. They are popular sport fish due to their size and fight. However, popularity has led to overfishing, threatening some tuna species. This article will provide a comprehensive overview of tuna, including biology, fishing practices, culinary uses, health concerns and conservation.

Tuna Species

There are 7 species in the Thunnus genus of tunas. They are:

• Albacore tuna – Reaches up to 4.6 ft (1.4m) and 133 lbs (60 kg)

• Southern bluefin tuna – Reaches up to 8 ft (2.5m) and 570 lbs (260 kg)

• Bigeye tuna – Reaches up to 8.2 ft (2.5m) and 460 lbs (210 kg)

• Pacific bluefin tuna – Reaches up to 9.8 ft (3m) and 990 lbs (450 kg)

• Atlantic bluefin tuna – The largest species, reaching up to 15 ft (4.6m) and 1,500 lbs (680 kg)

• Blackfin tuna – Reaches up to 3.6 ft (1.1m) and 49 lbs (22 kg)

• Yellowfin tuna – Reaches up to 7.9 ft (2.4m) and 440 lbs (200 kg)

There are 8 additional tuna species in 4 other genera, including skipjack, bullet, frigate, and mackerel tunas.

Biology and Physiology

Tuna are streamlined fish with tapered, torpedo-shaped bodies to reduce drag. Their sleek shape, combined with unique physiological adaptations, allow tuna to swim at fast speeds – up to 47 mph for yellowfin tuna.

Tuna are unique among fish in having higher body temperatures than the surrounding water. Special blood vessel networks allow them to conserve metabolic heat. Heated blood returning from the body core warms the cooler arterial blood via a counter-current heat exchange system. This allows tuna to thrive in a wide range of ocean temperatures.

Their compact, tapered bodies along with lunate-shaped tails provide hydrodynamic efficiency for fast swimming. Tuna also have finlets behind the dorsal and anal fins which improve straightline stability.

Global Tuna Fisheries

Tuna support extensive commercial fisheries for human consumption. The five main tuna species fished are skipjack, yellowfin, bigeye, albacore and bluefin tuna. The global tuna catch in 2007 exceeded 4 million tons, with skipjack comprising about 60 percent of the catch.

The Pacific Ocean accounts for around 68 percent of global tuna catch, followed by the Indian Ocean at 22 percent and the Atlantic at 10 percent. Purse seining makes up 62 percent of tuna catch, followed by longline fishing (14 percent) and pole-and-line fishing (11 percent).

Japan is the leading tuna consuming nation. Controversies have arisen over unsustainable quotas for Southern bluefin tuna by Japan and bluefin farming practices.

Tuna Culinary Uses

As food, tuna is popularly canned, smoked, grilled, fried and served raw as sushi and sashimi. Canned light tuna is commonly used in sandwiches, salads and pasta dishes. Albacore tuna is favored for canning over skipjack tuna due to higher fat content and flavor. Ventresca tuna comes from the fatty belly portion and commands high prices for premium canned tuna.

Sushi grade tuna like bigeye and bluefin are widely used in Japanese cuisine as sashimi and sushi. The high fat content and red coloration make these varieties most suitable for eating raw. Leaner tuna like skipjack can also be consumed raw but are not as desirable.

For cooked preparations, tuna steaks are popular grilled, pan-seared, baked or blackened. Tuna is also smoked, roasted whole, used in soups and stews or cooked into tuna salad and patties.

Health Concerns with Tuna

Due to tuna’s higher position in the food chain, mercury contamination can be a concern, particularly for pregnant women and children. Albacore and skipjack tuna generally have lower mercury levels than larger bluefin and bigeye tuna. The FDA and EPA provide guidelines for limiting tuna consumption to reduce mercury exposure.

Histamine toxicity due to scombroid poisoning can also occur if tuna is improperly refrigerated after capture. Proper freezing practices at sea help reduce risks of histamine build up. Fresh tuna has a short shelf life and should be consumed within days of catching.

Tuna are an excellent source of protein, omega-3 fatty acids, vitamin D, vitamin B12, niacin and selenium. However, the benefits need to balanced with potential mercury risks.

Tuna Conservation

Due to their high economic value and demand, some tuna species have been overfished. The Southern bluefin tuna is listed as critically endangered by the IUCN Red List. Bigeye, albacore and Atlantic bluefin are listed as vulnerable. However, Skipjack and yellowfin remain abundant.

International cooperation for improved monitoring and setting of catch limits is critical for the sustainability of global tuna fisheries. Bycatch from large driftnets and purse seines also needs to be reduced to protect dolphins and other marine life. Efforts are ongoing to make tuna fishing practices more responsible and environmentally friendly.

In conclusion, tuna are amazing fish perfectly built for speed and endurance. Their rich flavor and versatility as food comes at a cost of heavy fishing pressure. With proper management, tuna can continue meeting our dietary needs while their unique biology and migrations fascinate us for generations to come.