Blackfin tuna (Thunnus atlanticus) is the smallest tuna species in the Thunnus genus, generally growing to a maximum of 100cm (39 inches) in length an weighing 21kg (46 lbs). Blackfin have football shaped bodies, black backs with a slight yellow on the finlets, and have yellow on the sides of their body. Blackfin are only found in the western Atlantic from Cape Cod to Brazil.