Sonar operators, using the newly developed sonar technology during World War II, were puzzled by what appeared to be a false sea floor 300–500 metres deep at day, and less deep at night. At least one lanternfish was found with over 80 pieces of plastic chips in its gut, according to scientists monitoring ocean plastic in the Pacific Ocean's eastern garbage patch. Lanternfish themselves have been found to feed on bits of plastic debris accumulating in the oceans. The concentration of the photophores on the flanks of the fish also indicate the light's use as camouflage in a strategy termed counterillumination, the lanternfish regulate the brightness of the bluish light emitted by their photophores to match the ambient light level above, effectively masking the lanternfishes' silhouette when viewed from below.Ī major source of food for many marine animals, lanternfish are an important link in the food chain of many local ecosystems, being heavily preyed upon by whales and dolphins, large pelagic fish such as salmon, tuna and sharks, grenadiers and other deep-sea fish (including other lanternfish), pinnipeds, sea birds, notably penguins, and large squid such as the jumbo squid, Dosidicus gigas. The arrangements of lanternfish photophores are different for each species, so their bioluminescence is thought to play a role in communication, specifically in shoaling and courtship behaviour. Migration patterns may also depend on life stage, sex, latitude, and season. Some deeper-living species may not migrate at all, while others may do so only sporadically. Great variability in migration patterns occurs within the family. Due to their gas bladders, these layers are visible on sonar scans and give the impression of a "false bottom" this is the so-called deep-scattering layer that so perplexed early oceanographers (see below). Different species are known to segregate themselves by depth, forming dense, discrete conspecific layers, probably to avoid competition between different species. Most species remain near the coast, schooling over the continental slope. After a night spent feeding in the surface layers of the water column, the lanternfish begin to descend back into the lightless depths and are gone by daybreak. The lanternfish are thought to do this to avoid predation, and because they are following the diel vertical migrations of zooplankton, upon which they feed. Lanternfish are well known for their diel vertical migrations: during daylight hours, most species remain within the gloomy bathypelagic zone, between 300 and 1,500 m (980 and 4,920 ft) deep, but towards sundown, the fish begin to rise into the epipelagic zone, between 10 and 100 m (33 and 328 ft) deep. In life, shallow-living species are an iridescent blue to green or silver, while deeper-living species are dark brown to black. Lanternfish are generally small fish, ranging from about 2 to 30 cm (0.79 to 11.81 in) in length, with most being under 15 cm (5.9 in). This is true for the luminous caudal patches, with the males' being typically above the tail and the females' being below the tail. In some species, the pattern varies between males and females. The photophores emit a weak blue, green, or yellow light, and are known to be arranged in species-specific patterns. Some may also possess specialised photophores on the caudal peduncle, in proximity to the eyes (e.g., the "headlights" of Diaphus species), and luminous patches at the base of the fins. 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. Commercial fisheries for them exist off South Africa, in the sub-Antarctic, and in the Gulf of Oman. Lanternfish are among the most widely distributed, diverse and populous vertebrates, with some estimates suggesting that they may have a total global biomass of 550–660 million metric tonnes, accounting for up to 65% of all deep-sea fish biomass. 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. Lantern fishes are aptly named after their conspicuous use of bioluminescence. 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 (or myctophids, from the Greek μυκτήρ myktḗr, "nose" and ophis, "serpent") are small mesopelagic fish of the large family Myctophidae.
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