Atlantic Bluefin Tuna - Thunnus thynnus A highly migratory species found in the North Atlantic and the Mediterranean. This is a large and powerful fish that can reach lengths of up to 3 metres and weigh over 900 kilograms. Bluefin Tuna are voracious predatory fish that feed on smaller fish, squid and crustaceans. This species is of great economic importance with a fishery that is highly regulated to prevent over-fishing.