Product Code Database
Ridgeheads, also known as bigscales, are a family ( Melamphaidae, from the Greek language melanos black and amphi by) of small, deep-sea Beryciformes fish. The family contains approximately 37 species in five genus; their distribution is worldwide, but ridgeheads are absent from the Arctic Ocean and Mediterranean Sea. Although the family is one of the most widespread and plentiful of deep-sea families, none of its members are of interest to commercial fishery.
These fish are named for their large scales and pronounced cranial ridges, as well as for their typically dark brown to black coloration. Ridgeheads are the largest and most diverse family of their order.
The large scales are cycloid and imbricate; they are arranged in a longitudinal series of 12–40. Usually deciduous, these scales are largest in Scopelogadus species; in these and some other species, the scales' circuli (concentric lines) are clearly visible to the unaided eye. The lateral line (excluding the network of cranial canals) is largely absent; when present, it is reduced to 1–2 pored scales following the operculum's upper edge. The caudal peduncle is relatively long; the caudal fin is forked to emarginate and possesses 3–4 procurrent spines. The single dorsal fin originates behind the pectoral fin and and contains 1–3 weak spines and 9–18 soft rays; the pectoral fins are elongate and tapered (the superior rays being longer than the inferior rays) and contain 12–16 soft rays. The pelvic fins are thoracic to subthoracic with one spine and 6–8 soft rays; the anal fin is small and set far back, with one spine and 7–11 soft rays.
The branchiostegal rays number 7–8 and the 24–31. The largest species recorded is Poromitra curilensis, a Pacific ridgehead related to the crested bigscale, at up to 18 centimetres standard length (SL; a measurement excluding the caudal fin). Most ridgeheads are well under 10 centimetres SL.
The family is sometimes termed pseudoceanic because, rather than having an even distribution in open water, ridgeheads occur in significantly higher abundances around structural oases, notably and over continental slopes. This is also true of other deep-sea pelagic groups, such as the lanternfish (Myctophidae), marine hatchetfish (Sternoptychidae), and Phosichthyidae (Phosichthyidae or Photichthyidae) families. The phenomenon is explained by the likewise abundance of prey species which are also attracted to the structures.
As oviparous pelagic spawners, ridgeheads produce many tiny roe which are fertilization externally; the eggs and larvae (and early juveniles) are buoyant and , drifting with the currents near the surface until the juveniles have reached the point where they are strong enough to determine their own direction. Study of the spawning habits of twospine bigscales ( Scopelogadus mizolepis bispinosus) indicates spawning occurs year-round, with no definite peaks.
Although their deep-living nature protects them from predation to some degree, ridgeheads are prey to large such as ; large squid such as the Jumbo Squid ( Dosidicus gigas) and Sevenstar Flying Squid ( Martialia hyadesii); (family Delphinidae); and large pelagic fish, such as tuna and other scombridae.
|
|
