Bluefin tuna

Bluefin tuna

Bluefin tuna tuna Bluefin tuna Bluefin tuna

Like all tuna, the bluefin is a saltwater finfish who is part of the mackerel family. For many years, bluefin tuna have been fished extensively leading to severe overfishing. This month, we list 10 cool things about bluefin tuna!

 

  1. Fishy giant

Adults are typically 3m in length, but can reach 4m, making the Atlantic tuna one of the largest bony fishes and the largest of all tuna species. Adults average 130 to 679kg, although the upper weight range is rarer now.

 

  1. ‘Aerodynamic’

Bluefin tuna are built like torpedoes. Not only do they have a hydrodynamic shape, their pectoral (side) fins can be retracted and, unlike other fish, their eyes are set flush to their body. This means their bodies create little drag as they swim through water.

  1. Diverse

There are eight species of tuna and four of these are part of the bluefin family: Atlantic bluefin or northern bluefin, Pacific bluefin, southern bluefin and the longtail tuna. The other four species are the albacore, bigeye, blackfin and yellowfin.

  1. 10 million eggs

Atlantic bluefin tuna spawn just once a year and do not reach reproductive maturity until they are eight to 12 years old. This makes bluefin tuna more vulnerable to overfishing than some of the smaller tuna species that can spawn several times in a year. Female Atlantic bluefin can produce up to 10 million eggs per year, but just a small fraction survives to adulthood.

 

  1. Very fast

They typically swim at speeds of between 7 and 15km/h, but when chasing prey or to avoid predators, they can swim up to 71 to 100km/h. Capable of beating their tailfins some 30 times per second, the tail of a swift bluefin appears only as a blur to the human eye.

  1. Big money

In January 2012, a prime 269kg bluefin tuna sold in a Japanese fish market for $736,000 (about R9 million!).

  1. Big bellies

Bluefins reach their enormous size by gorging themselves almost constantly on smaller fish, such as crustaceans, squid and eels. They will also filter-feed on zooplankton and other small organisms. The largest tuna ever recorded was an Atlantic bluefin who weighed 679kg.

 

  1. Well camouflaged

Tuna school tuna Bluefin tuna Tuna schoolTheir colouring – metallic blue on top and shimmering silver-white on the bottom – helps camouflage them from above and below.

 

  1. Endangered

Sadly bluefin tuna have been severely overfished in our oceans, making them highly vulnerable. The Marine Conservation Society advises that Atlantic bluefin, Pacific bluefin and southern bluefin tuna meat be avoided by consumers as continued fishing of wild populations is not sustainable.

 

  1. Sixth sense?

Bluefin have many senses of direction. They can use their pineal window to follow the sun and celestial cues. They make use of their visual, olfactory and electromagnetic senses to stay on course or follow prey. Furthermore, they are thermotactic (movement of an organism toward or away from a source of heat).

Text: Shannon Wilding
The full article appears in the October issue of Animaltalk.