ClassACTINOPTERYGII Ray-finned fishes
GeneraAristostomias(1) Astronesthes(13) Bathophilus(6) Borostomias(2) Chauliodus(1) Echiostoma(1) Eupogonesthes(1) Eustomias(15) Flagellostomias(1) Heterophotus(1) Idiacanthus(2) Malacosteus(2) Melanostomias(6) Neonesthes(2) Opostomias(1) Pachystomias(1) Photonectes(8) Photostomias(4) Rhadinesthes(1) Stomias(3) Thysanactis(1) Trigonolampa(1)
A very diverse group of elongate deep-sea predators with rows of light organs or photophores along the lower sides of the body, large jaws with prominent canine and sometimes fang-like teeth, and a chin barbel usually tipped with a bioluminescent lure.
Stomiids not only have the pectoral girdle separated from the skull, they also have a flexible connection between the occiput and the first vertebra, where only the notochord persists (Schnell & Johnson 2017). The enables dragonfishes to open their mouths very wide, allowing them to swallow large prey items.
Work is in progress to help determine relationships within the family, which currently comprises six subfamilies.
Photophore terminology: AC – ventral series posterior to anal-fin origin; AOP – preorbital light organ anteroventral to eye; IC – ventral series from anterior isthmus to caudal fin; IP – ventral series anterior to pectoral-fin base; IV – ventral series anterior to ventral-fin base; OA – lateral series; OV – lateral series from behind operculum and above pectoral-fin base to above and just before ventral-fin base; Po – postorbital photophore posteroventral to eye; PV – ventral series between bases of pectoral and ventral fins; Sor – suborbital photophore anteroventral to eye; VAL – lateral series from just behind ventral-fin base to just behind anal-fin origin; VAV – ventral series between ventral-fin base and anal-fin origin.
|A large family comprising 28 genera with more than 292 species in 5 subfamilies; about 70 species in 20 genera are known from Australian waters.|
|Midwater predators found in all oceans. Stomiids are epi-, meso- and bathypelagic in the open ocean to 4500 m, and of a few species migrate to surface waters at night.|
All subfamilies share the following characters: Body elongate, serial photophore rows on abdomen; true gill rakers absent in adults, one infraorbital bone (vs two in other stomiiforms), supramaxillary single if present, mesopterygoid reduced or absent, most with a chin barbel associated with hyoid bone and tipped with a bioluminescent lure. Mouth large, often with fang-like teeth.
Subfamily Astronesthinae (Snaggletooths): Scales absent, dorsal-fin origin at about midbody, over or behind pelvic-fin base, well in advance of anal-fin origin; dorsal adipose fin present in most, ventral adipose fin before anal fin present in many; chin barbel present, with terminal bulb in some; ventral rows of photophores, body with patches of luminous tissue, mouth large teeth elongate. Reach about 30 cm.
Subfamily Chauliodontinae (Viperfishes): Body elongate, slender, compressed, covered with a gelatinous membrane; unique among stomiiforms in having a short-based dorsal fin just behind head, well before pelvic fins; first dorsal ray greatly elongate, tipped with small flap; premaxilla and lower jaw with huge fang-like teeth; chin barbel short if present; dorsal adipose far back on body, ventral adipose fin before anal fin. Body with five longitudinal rows of large deciduous scales, each with a hexagonal pigment pattern and a small photophore; large photophores in two ventrolateral rows with irregular rows of smaller photophores; branchiostegal membranes with photophores, pre- and postorbital photophore present. Reach 30 cm.
Subfamily Idiacanthinae (Black Dragonfishes): Body extremely long, slender body, almost eel-like, sexually dimorphic; dorsal-fin extremely long, anal fin about half body length, both bases ending just before caudal fin, base of each dorsal- and anal-fin ray with a spur on each side; pectoral fin absent in adults; lateral and ventral rows of photophores; minute photophores scattered over head and body; postorbital photophore sexually dimorphic; chin barbel absent in males, which retain some larval characteristics. Larvae distinctive, very long, slender; early stages with prominently stalked eyes allowing for increased field of vision, eye stalks reaching up to one-third body length. Advanced larvae sexually dimorphic, males much smaller than females, lacking teeth, chin barbel, a functional gut and pelvic fins. Reach 48 cm.
Subfamily Malacosteinae (Loosejaws): Body elongate, head large, eye large, head and snout profile rounded; mouth enormous, jaws elongate, reaching beyond skull; jaws lack membrane in floor of mouth, allowing jaws to expand widely during feeding; lower jaw connected to branchiostegals and retracted by thin band of muscle attached to tip of lower jaw; first few vertebrae unossified allowing head to swing vertically and very large prey items to be swallowed; dorsal-fin origin far behind pelvic fin, over anal fin; adipose fin and scales absent; chin barbel in most; pectoral fins absent in some; anterior and postorbital photophores present. Reach 24 cm.
Subfamily Melanostomiinae (Scaleless Black Dragonfishes): The largest subfamily, with an elongate body, dorsal and anal fins are opposite and set far back on the body, two ventrolateral rows of photophores, large jaws with canine teeth, no true gill rakers as adults and a simple to complex bioluminescent chin barbel. The skin is naked with small secondary photophores often scattered over the head, body and fin rays, especially in vertical rows between the myomeres, and additional luminous tissue may be present. Reach more than 50 cm.
Subfamily Stomiinae (Scaly Dragonfishes): Body elongate, slender, compressed,; mouth with large, teeth large, fang-like, chin barbel prominent; dorsal fin placed far posterior, above anal-fin base, adipose fin absent; body with 5-6 longitudinal rows of scales, each with a hexagonal pigment pattern and a small photophore; postorbital photophore below eye, two longitudinal photophore rows ventrolaterally on body, small photophores on branchiostegals. Reach about 41 cm.
|Maximum length 50 cm.|
|Generally black fishes, with rows of primary photophores and a range of smaller secondary photophores, plus other patches of luminous tissue. Some species have a brassy sheen to the body.|
|Most stomiids are voracious predators and feed mostly on midwater fishes and crustaceans. Dragonfishes are morphologically adapted to swallow relatively large prey in relation to their body size, and feed on whatever they can swallow. Feeding adaptations include an enormous mouth gape, fewer yet larger teeth, recurved teeth in the back of the mouth to aid swallowing, reduced or absent gill rakers and unossified anterior vertebrae allowing the fish to throw its head back. The viperfish, Chauliodus sloani, for example, has huge fangs, hinged jaws to increase the gape of the mouth, and unossified vertebrae so that large fishes can be swallowed. The Black Loosejaw, Malacosteus niger, also feeds on zooplankton, with small crustaceans, such as copepods, comprising about 60% of the diet. This is surprising, as not only does the Loosejaw have the morphological characters listed above, it also lacks a floor to its mouth, and seems to be poorly adapted to retain such small prey items in its mouth.|
Subfamily Astronesthinae (Snaggletooths): Oviparous, eggs unknown. Larvae rare and highly diverse; elongate, gut trailing, pigment variable, dorsal fin positioned anteriorly, in advance of anal fin, eyes not stalked.
Subfamily Stomiinae (Scaly Dragonfishes): Oviparous, eggs and larvae pelagic; larvae similar to those of Chauliodontinae, but with shorter preanal length, head relatively small, longer snout, early developing finrays and heavier body pigment.
Subfamily Chauliodontinae (Viperfishes): Oviparous with large, round planktonic eggs; larvae elongate, yolk-sac elongate, gut almost as long as body, head short, snout pointed, eyes oval; with little or no pigment and somewhat flaccid bodies, fin rays develop slowly and larvae transform at a large size.
Subfamily Idiacanthinae (Black Dragonfishes): Oviparous; larvae distinctive, very long, slender; early stages with prominently stalked eyes allowing for increased field of vision, eye stalks reaching up to one-third body length. Advanced larvae sexually dimorphic, males much smaller than females, lacking teeth, chin barbel, a functional gut and pelvic fins.
Subfamily Melanostomiinae (Scaleless Black Dragonfishes): Oviparous with pelagic eggs; larvae diverse, many elongate with voluminous finfolds and trailing guts; head large, snout pointed, eye small, sometimes telescopic; dorsal and anal fins far back on body; larval pigment in series.
Subfamily Malacosteinae (Loosejaws): Oviparous, eggs unknown, larvae rare, elongate, slender, head depressed, snout elongate, eye small, jaws large; gut slender, trailing well beyond body, usually pigmented.
|Although of no interest to fisheries, some species are frequently taken as bycatch by commercial trawlers when the nets are lowered and retrieved through deep pelagic waters.|
|Males of Idiacanthus are extremely sexually dimorphic and are very small, even as adults. They grow to about one-sixth the size of adult females and retain many larval features.|
Photophore terminology in Stomiidae:
AC – ventral series posterior to anal-fin origin
AOP – preorbital light organ anteroventral to eye
IC – ventral series from anterior isthmus to caudal fin
IP – ventral series anterior to pectoral-fin base
IV – ventral series anterior to ventral-fin base
OA – lateral series
OV – lateral series from behind operculum and above pectoral-fin base to above and just before ventral-fin base
Po – postorbital photophore posteroventral to eye
PV – ventral series between bases of pectoral and ventral fins
Sor – suborbital photophore anteroventral to eye
VAL – lateral series from just behind ventral-fin base to just behind anal-fin originVAV – ventral series between ventral-fin base and anal-fin origin.
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