What is special about a bluefin tuna?

There are four types of bluefin tuna:

Pacific bluefin - up to 3 m (9.8 ft) long and 450 kg (990 lb)

Atlantic bluefin - up to 4.6 m (15 ft) and 450 kilograms (990 lb) - there may be some evidence that the species can reach 910kg (2,000lb), but this is not confirmed.

Longtail - up to 145 cm (57 in) long and 35.9 kilograms (79 lb)

Southern bluefin - up to 2.5 m (8.2 ft) and 400 kg (882 lbs)