The humpback anglerfish (Melanocetus johnsonii) is a species of black seadevil in the family of Melanocetidae, which means "black sea monster". The species is named after James Yate Johnson, an English naturalist who discovered the first specimen in Madeira in 1863. The common names include anglerfish, viperfish, and fangtoothfish.
Historical background The first specimen of M. johnsonii was discovered by English naturalist James Yates Johnson near Madeira, an archipelago off the coast of northwestern Africa, on December 24, 1863. The specimen was brought to Albert Carl Ludwig Gotthilf Günther, keeper of zoology at the Natural History Museum in London. He described it as "a fish which proves to be the type of a new genus, not only on account of its extraordinary form, but also on account of the absence of pelvic fins." Günther was the first to record the unique morphology of the species; he named it after Johnson, the initial collector. Early hypotheses about anglerfish behavior posited that their illicium and esca, the extended dorsal fin spine and bulbous apparatus that protrude from the snout, are used for luring prey. The Danish naturalist Christian Frederik Lütken was the first to suggest that this feature was central in feeding behavior. Until the 1920s, male specimens without a luring apparatus had been thought to be distinct, and were placed in separate taxonomic categories from their female counterparts. In 1924, British ichthyologist Charles Tate Regan realized that a small fish attached to a larger anglerfish was a male in the process of reproduction, leading to the discovery of the sexual dimorphism that characterizes anglerfish. Several specimens that were previously categorized as separate species, including M. ferox and M. krechi, have since been recognized as synonyms of M. johnsonii.
Habitat M. johnsonii inhabits the mesopelagic and bathypelagic zones, and is found most commonly at depths between 200 and 1,500 metres (660 and 4,920 ft). Compared to other species in the genus, M. johnsonii is more likely to be found at shallower depths; 65% of recorded specimens were collected at depths of or above 1,000 metres (3,300 ft) below the surface of the water. At these depths, there is little to no light penetrating from the surface photic zone. Because of this, the humpback anglerfish has evolved means of predation using bioluminescence based on the constraints of their habitat. M. johnsonii has the widest geographic distribution of all the species within the Melanocetus genus. The species had been known to be widely distributed in the temperate and tropical ranges of all oceans, as well as in the South China Sea and the East China Sea. Its southern geographic distribution was expanded in 2014 when the first specimen of M. johnsonii in Antarctic waters was obtained from the stomach of an Antarctic toothfish in the Ross Sea. The specimen was identified by morphologic methods and further genetic analysis using the fish's pectoral fin clip which verified that the specimen belonged to M. johnsonii. An individual specimen of M. johnsonii was found near Father Charles Canyon in British Columbia, extending its known northern distribution in the East Pacific and solidifying it as one of the most widely distributed anglerfish.
Morphology M. johnsonii is a black soft-bodied anglerfish that is dark brown or black in color. Female humpback anglerfish have short, globular bodies, large heads with a widened mouth that is nearly vertical, and long pointed teeth capable of eating prey larger than themselves. Numerous small skin spines are found under the dorsal fin. Compared to other species within the genus, M. johnsonii has a longer illicium and fewer jaw teeth, but these teeth are relatively longer than those of other species. Like all other anglerfish, females have a short dorsal fin spine (illicium) with a bulbous luring apparatus (esca) on the snout. The esca has compressed posterior and anterior crests, noted when distinguishing it from other anglerfish. Unlike other species in the genus, females of the species have a nearly straightened anterior margin of vomer. Female M. johnsonii have small, subcutaneous eyes that may suggest their lack of dependency on visual sight for feeding and reproduction. Humpback anglerfish exhibit extreme sexual dimorphism, with larger sized females and dwarfed males. Females have been found to grow up to 153 mm, while males grow only between 15.5 and 28 mm. Males lack a luring apparatus, but have large eyes and nostrils which may be helpful for locating far dispersed mates. While distinguishing characteristics of males in the genus are not well defined, M. johnsonii males usually have a relatively larger number of denticular teeth and dorsal and pectoral fin rays. However, since only eight male specimens were obtained up to date, information concerning males is limited. Also, as there are many similarities in the morphological characteristics of M. johnsonii and M. rossi, one distinguishing feature is that M. johnsonii has black pigmentation on its upper body exterior while M. rossi does not. Because of the numerous similarities between the two, it has been suggested that M. rossi may be a synonym of the M. johnsonii species.
Feeding behavior
M. johnsonii females have large mouths filled with sharp teeth and large stomachs that make them capable of eating nearly everything they encounter. Their stomachs are highly distensible and expand easily, allowing them to consume meals weighing more than themselves. One M. johnsonii individual weighing 8.8 grams was retrieved using a trawl, and the specimen was found to have three snipe eels totaling 12.3 grams in its stomach.
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