Bismihi Subhanahu Wa-ta'ala Assalamooalaikum Warahmatullahi Wabarakatuh Respected Brother or Sister,
Tuna is Halaal as it is a fish.
Definitions: a. Important warm-water fatty fish of the genus Thunnus of the family Scombridae; usually served as steaks. b. Any very large marine food and game fish of the genus Thunnus; related to mackerel; chiefly of warm waters.