Lanternfish

Lanternfish (or myctophids, from the Greek μυκτήρ myktḗr, "nose" and ophis, "serpent") are small mesopelagic fish of the large family Myctophidae. One of two families in the order Myctophiformes, the Myctophidae are represented by 246 species in 33 genera, and are found in oceans worldwide. Lanternfishes are aptly named after their conspicuous use of bioluminescence. Their sister family, the Neoscopelidae, are much fewer in number but superficially very similar; at least one neoscopelid shares the common name "lanternfish": the large-scaled lantern fish, Neoscopelus macrolepidotus. Lanternfish are among the most widely distributed, diverse and populous vertebrates, with some estimates suggesting that they may have a total global biomass of 1.8 to 16 gigatonnes, accounting for up to 65% of all deep-sea fish biomass. Commercial fisheries for them exist off South Africa, in the sub-Antarctic, and in the Gulf of Oman. Lanternfish typically have a slender, compressed body covered in small, silvery deciduous cycloid scales (ctenoid in four species), a large bluntly rounded head, large elliptical to round lateral eyes (dorsolateral in Protomyctophum species), and a large terminal mouth with jaws closely set with rows of small teeth. The fins are generally small, with a single high dorsal fin, a forked caudal fin, and an adipose fin. The anal fin is supported by a cartilaginous plate at its base, and originates under, or slightly behind, the rear part of the dorsal fin. The pectoral fins, usually with eight rays, may be large and well-developed to small and degenerate, or completely absent in a few species. In some species, such as those of the genus Lampanyctus, the pectorals are greatly elongated. Most lanternfish have a gas bladder, but it degenerates or fills with lipids during the maturation of a few species. The lateral line is uninterrupted. In all but one species, Taaningichthys paurolychnus, a number of photophores (light-producing organs) are present; these are paired and concentrated in ventrolateral rows on the body and head.