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October 25, 2001

Bonito or Tuna

What's the difference between a tuna and a bonito?

Q: What's the difference between a tuna and a bonito? Anglers in some areas like the Florida Keys may catch any of three species of small tuna: Little tunny, the skipjack tuna and the Atlantic bonito are all called "bonito." - Albert Weisman, Boston, Massachusetts

A: There is very little practical difference. Tunas, bonitos and mackerels are all members of the same family: Scombridae. About 13 species are called tunas, eight bonitos and six mackerels. "True" tunas, as scientists call them, belong to the tribe Thunnini. All others are called "tuna-like" fishes. The skipjack tuna (Katsuwonus pelamis) and the little tunny (Euthynnus alletteratus) - both "true" tunas - might be called bonitos because, like most bonitos, they are small and have dark stripes or spots on their sides, while the majority of true tunas are larger and have no dark markings.
True tunas are also generally rounder in cross section than their mackerel relatives, and their first and second dorsal fins are closer together than in mackerels, but these characteristics can't be used to distinguish tunas and bonitos from each other. Among scombrids found in the Florida Keys, for example, the skipjack tuna, the little tunny and the Atlantic bonito (Sarda sarda) are quite similar to each other in size, shape, fin spacing, numbers of dorsal spines and even markings. The little tunny and the Atlantic bonito both have dark lines on their backs - wavy lines on the little tunny (sometimes accompanied by a handful of spots on the chest) and straighter lines on the Atlantic bonito. The skipjack tuna is distinguished by having its lines on its belly.
In the Florida Keys, the most common difference between tunas that are called tunas and tunas that are called bonitos may be their value: "Tunas" are the fish people prefer to eat, and bonitos are the fish they release or use for bait.