Euthynnus affinis or also known as Kawakawa, is a species of the family Scombridae, classified in the order perciformes and class Actinopterygii. It inhabits the temperate waters of both the Indian and Pacific Oceans. It is a species that inhabits the so-called epipelagic and neritic zones, that is to say waters that receive sunlight (epipelagic) and are not in direct contact with the coast (neritic). It is a very common species in the atolls of the Indo-Pacific.
The body of Euthynnus affinis is fusiform, reaching 100 cm in length and up to 14 kg in weight, although it is common to find slightly smaller specimens. It has two dorsal fins, the first of them formed by 11-14 spines, the first spines being higher than the middle ones. The second dorsal fin is separated from the first by a small interspace, its spines being lower than those of the first dorsal fin. Behind this second dorsal fin, we find between 8 and 10 secondary fins. The pectoral fins are short and the anal fin is formed by 13 to 14 rays. The caudal peduncle is equipped with two small keels on each side, located at the base of the caudal fin. As for the color of Euthynnus affinis, the back parto of its body is blackish blue, while its belly is silver. Numerous thin, oblique, bright dark blue stripes are located above the lateral line. These stripes do not extend beyond the first half of the first dorsal fin. It also has one or more small black spots between the pelvic and pectoral fins, although these spots are not always visible.
Euthynnus affinis is a species that shows some social behavior. It is common to observe it forming large schools together with specimens of other species that have similar sizes to them. For example, juvenile individuals of the species Thunnus albacares, Jatsuwonus pelamis, Auxis spp, and Megalspis cordyla are frequently observed together with the Euthynnus affinis.
An opportunistic predator, this species will feed indiscriminately on fish, shrimp and cephalopods. From the reverse point of view, marlins and sharks are its major predators.
The reproduction of Euthynnus affinis occurs at different times depending on geography. In the Philippines it has been described that the breeding peak occurs between March and May, in the Seychelles from October to November and from April to May, in East Africa from January to July, and in Indonesia in October. In any case, the clutches of this species are very numerous, estimated between 200,000 and 600,000 eggs per clutch, with a total of 4 clutches per year.
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