Ridgehead

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Ridgehead
Scopelogadus mizolepis mizolepis
Scientific classification Edit this classification
Domain: Eukaryota
Kingdom: Animalia
Phylum: Chordata
Class: Actinopterygii
Order: Beryciformes
Family: Melamphaidae
T. N. Gill, 1893
Genera

Melamphaes
Poromitra
Scopeloberyx
Scopelogadus
Sio

Ridgeheads, also known as bigscales, are a

stephanoberyciform fish. The family contains approximately 37 species in five genera; 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.

Description

Typical of the Stephanoberyciformes, the melamphid body is robust, oblong,

Poromitra megalops
they may exceed 20 per cent of the head's length in diameter.

The large scales are cycloid and imbricate; they are arranged in a longitudinal series of 12–40. Usually deciduous, these scales are largest in

anal fin
is small and set far back, with one spine and 7–11 soft rays.

The

crested bigscale,[1] at up to 18 centimetres standard length (SL; a measurement excluding the caudal fin).[2]
Most ridgeheads are well under 10 centimetres SL.

Life history

In addition to cranial ridges, the head of Melamphaes suborbitalis also features strong post-temporal spines directed antero-dorsally. The fine teeth lining the fish's jaws, its procurrent caudal spines, and scale circuli are also visible.

Ridgeheads are meso- to

euphausiids, and other small pelagic crustaceans. There is also a marked segregation of life stages: larval
and juvenile ridgeheads are present within the upper 200 metres of the water column, whereas adults are typically found much farther down.

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

continental slopes. This is also true of other deep-sea pelagic groups, such as the lanternfish (Myctophidae), marine hatchetfish (Sternoptychidae), and lightfish
(Phosichthyidae or Photichthyidae) families. The phenomenon is explained by the likewise abundance of prey species which are also attracted to the structures.

As

fertilized externally; the eggs and larvae (and early juveniles) are buoyant and planktonic, 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

Jumbo Squid (Dosidicus gigas) and Sevenstar Flying Squid (Martialia hyadesii); oceanic dolphins (family Delphinidae); and large pelagic fish, such as tuna and other scombrids
.

References

  1. doi:10.1134/S0032945208080018
    .
  2. JSTOR 1444136
    .

Further reading
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