Butterfly kingfish

The juveniles of the butterfly kingfish are characterized by enormous pelvic fins that are longer than the length of its head, and that become more proportional as the fish grows. At any size, the pelvic fin tucks into a deep ventral groove, in much the same way as the first dorsal spines do in all scombrids. This species has very large cycloid scales, below which is a thick layer of fat. The swim bladder has two anterior projections that extend into the back of the skull, near the inner ear. Most bony fishes are ectothermic, or cold-blooded, but this species, much like the related tunas, is endothermic and is able to raise its body temperature to achieve a degree of thermoregulation. It has a brain heater organ derived from the lateral rectus eye muscle, which is distinct from that of the billfishes, whose heater is derived from their superior rectus muscles. ==Etymology==

Gasterochisma derives from the , and ('''') "crossing; X-shaped; sign of the 'X'". ==Taxonomy==

The evolutionary lineage of the butterfly kingfish is more primitive and quite different from that of the rest of the scombrids. Additionally, the morphology of this species is substantially different from that of the others – some suggest that it might belong in a different family altogether. At present, however, morphology and nuclear phylogeny provide support that Gasterochisma is sister to all other scombrids, and that both its genus, Gasterochisma, and its subfamily, Gasterochismatinae, remain as monotypic taxa under the family Scombridae. The following cladogram shows the most likely evolutionary relationships between the butterfly kingfish and the tunas, mackerels, Spanish mackerels, and bonitos. ==Distribution==

The butterfly kingfish has a circumglobal distribution in southern temperate waters. It has caught as far north as Hawaii and seems to be common around Oceania. It prefers waters between . == Fisheries ==

While a rare catch, there is a minor commercial market, where they are caught incidentally while targeting other fish, especially through the use of longline fishing. It is of minor importance to recreational Fisheries. ==References==