Auxis

There are four species in the genus Auxis, which were formerly regarded as two polytypic species, each with two subspecies.[1]

• Auxis brachydorax Collette & Aadland, 1996
• Auxis eudorax Collette & Aadland, 1996
• Auxis rochei Risso, 1810 (Bullet tuna)
• Auxis thazard Lacépède, 1800 (Frigate tuna)

Auxis can reach a length of 50–65 millimetres (2.0–2.6 in). They have a strong, fusiform body with a sharpened head. The teeth are small and conical. The two dorsal fins are separated by a wide gap. The pectoral fins are short. They have a dark, blue-black back, the top of the head may be deep purple or almost black. The belly is whitish and without streaks or spots.

These fishes are widespread in all tropical and subtropical seas and oceans, and both mentioned species are present in the Mediterranean Sea with their subspecies (A. thazard thazard and A. rochei rochei'’).

Auxis species are the predominant prey of pelagic gamefish off of the east coast of the United States.[2]

In Japan the two species in the genus are collectively called sōdagatsuo (Japanese: ソウダガツオ,宗太鰹), and this is also the common genus name. In Japanese cuisine, these fish are processed into sōdabushi, a product much like katsuobushi, though not really used in fine-dining restaurants or as condiment, but as a fish stock ingredient at more budget type popular-dining places, e.g., soba noodle shops.

Although fresh fish might be eaten as sashimi or grilled, it has a lot of dark-red meat (chiai), so it is valued much less than the similar katsuo (skipjack tuna). And it degrades quickly so shipment out to market is limited. The frigate tuna (hirasoda) is considered superior between the two.

Fossil of Auxis propterigius from Monte Bolca

Fossils of Auxis have been found in the Pliocene of Italy and United States (age range: from 5.3 to 3.6 million years ago.).[3]

• Froese, Rainer and Pauly, Daniel, eds. (2006). Species of Auxis in FishBase. January 2006 version.
• MNHN