Lampridiformes

(Opah and relatives)

Class Actinopterygii

Order Lampridiformes

Number of families 7

Evolution and systematics

The order Lampridiformes contains some of the most uniquely evolved, morphologically diverse, and colorful forms of living fishes. The imaginative common names of these species (oarfish, ribbonfish, tube-eye, inkfish, and unicornfish), their extreme rarity, and their fanciful reputations combine to promote the assemblage as subjects of public curiosity. In turn, scientists have particular interest in the group, because its members include species that are basal sister taxa in phylogenetic analysis of higher perchlike fishes and because many lampridiform species have evolved highly specialized traits. The icon of the order, Regalecus glesne, is a fabled species whose tremendous length (up to 55 ft, or 17 m—the longest of all bony fishes), bright crimson fins, long dorsal rays, silvery form, and tendency to appear suddenly at the ocean surface after wind storms brought fearful cries of "sea monster!" from ancient mariners. Recently, living oarfish have been sighted and filmed by divers in the clear waters of the Caribbean, and these accounts have stirred considerable popular interest. The order includes the deep-bodied Lampris guttatus, a brightly colored and heavy species (up to 600 lb, or 275 kg) that brings good prices in commercial markets, as well as other, lesser known and much smaller species that are never seen by the public and only infrequently collected on scientific expeditions.

In all, the order Lampridiformes (formerly known as the Allotriognatha) comprises 21 extant species classified in 12 genera and seven families. Skeletal evidence of another six or so extinct species has been found in fossil beds around the world. The current lampridiform classification is as follows: family Veliferidae, with two monotypic genera (containing one species), Velifer and Metavelifer; family Lamprididae, with one genus, Lampris (two species); family Stylephoridae, with one monotypic genus, Stylephorus; family Radiicephalidae, with one monotypic genus, Radiicephalus; family Lophotidae, with two monotypic genera, Lophotus and Eumecichthys; family Trachipteridae, with three genera, Trachipterus (four species), Zu (two species), and Desmodema (two species); and family Regalecidae, with two monotypic genera, Regalecus and Agrostichthys.

The oarfish and its relatives form a natural assemblage of fishes that evolved from a common Velifer-like ancestor sometime in the late Cretaceous or early Eocene. Independent investigations of lampridiform evolution, one using only morphological characters and another using both morphological and molecular characters in a total-evidence analysis, agree on the following shorthand pattern of phylogenetic relationships of lampridiform families: Veliferidae (Lamprididae (Stylephoridae ((Lophotidae + Radiicephailidae) (Regalecidae + Trachipteridae)))). In this shorthand scheme, sequentially, the taxon on the left and outside the parentheses is the sistergroup to the taxa within the parentheses. Thus, Veliferidae is the sistergroup to Lamprididae plus all other lampridiforms. Likewise, Lamprididae is the sistergroup to Stlylephoridae and all other lampridiforms. Finally, Stylephoridae is the sistergroup to two clades, each containing two families. To date, there have been no phylogenetic studies of species-level relationships, and, in some families, species-level and genera-level revisions are required.

Until recently, the limits of Lampridiformes and the systematic position of the order within the larger context of other bony fishes have been difficult, unresolved issues. Some scientists have provisionally included other families of deep-sea fishes (e.g., Ateleopodidae, Mirapinnidae, and Megalomycteridae) in Lampridiformes, but recent phylogenetic analysis confirms that these additional families are unrelated. Lampridiform fishes lack certain specializations of the axial skeleton (principally, patterns of small bones and ligaments

associated with anterior vertebrae) that characterize more advanced fishes. These higher taxa, collectively classified as the Acanthomorpha, include the beardfish (Polymixia) and numerous major categories, including the codlike fishes (Paracanthopterygii) and perchlike fishes (Perciformes). Otherwise, Lampridiformes possess many other acanthomorph traits. Thus, the order Lampridiformes is considered the primitive sister taxon to all higher fishes, a significant group making up approximately 60% of all known teleost species. This systematic position makes the order, especially its basal members, veliferid lampridiforms, important to scientists hoping to unravel the intricate evolutionary histories of the diverse assemblage of acanthomorph fishes.

Abrupt transitions from shallow, nearshore habitats to the open ocean and from deep-bodied (termed bathysomous forms) to elongate (taeniosomous) forms are two major events hypothesized to have shaped the evolution of Lampridiformes. The basal and most generalized lampridiform family is the Veliferidae, moderate-sized, shallow-dwelling fishes that reside in coastal seas. All other lampridiforms are open-ocean, epipelagic or mesopelagic fishes. Since veliferids are the basal sister group to the Lamprididae (plus all other lampridiforms), it appears that an early important event in the evolution of the lampridiform lineage was the invasion and subsequent adaptation of veliferid-like progeny to pelagic life in the deep ocean. Lampris, a ponderous and deep-bodied species, is the sister group to the tube-eyes (Stylephoridae) and all other lampridiforms. The second significant evolutionary transition occurs at this level in the phyletic sequence, because tube-eyes and their relatives are all slender, elongate, ribbon-shaped species. As the most highly evolved taxa of the order, Stylephorus is the sister taxon to two distinct clades in the lampridiform lineage, the inkfishes (represented by Lophotidae and Radiicephalidae) and the oarfishes and ribbonfishes (Regalecidae and Trachipteridae).

Numerous fossil forms have been attributed to lampridiform ancestry, some of which may be incorrectly classified. The oldest known lampridiform fish is Nardovelifer altipinnis, a recently described fossil found in Cretaceous deposits of Nardo near Lecce, in southern Italy. Eocene deposits near Verona, Italy, have yielded two species, Veronavelifer and Bajaichthys. Additional fossil taxa include several very large (up to 10 ft, or 3 m, in length) Lampris-like species discovered in Miocene deposits in California (Lampris zatima) and Oligocene deposits in New Zealand (an new, unnamed taxon) as well as two Oligocene lophotids, Protomecicthys and Protolophotus.

Physical characteristics

Unlike all other teleostean fishes, lampridiforms lack a ligamentous connection between the bones of the upper jaws (maxillae) and the cheekbones. In addition, the nasal cartilage that partially supports the maxillae is large and inserted in a groove on the skull in the frontal region. These two features allow the upper jaws of lampridiforms to be carried far forward during feeding, a modification that results in extreme jaw protrusion and expansion. In one species, Stylephorus chordatus, jaw protrusion allows the mouth cavity to expand suddenly to 40 times that of the closed mouth and permits Stylephorus to capture small planktonic prey items with considerable suction. Other unique physical characteristics of the order include crimson red fins, brightly colored bodies, and anterior placement of the thin bones (pterygiophores) that support the first dorsal fin. The elongate forms possess 60–150 vertebrae, whereas veliferids and lampridids have 33–46 vertebrae.

Distribution

Examples of most lampridiform families are rarely seen alive, and distribution records usually result from dead or dying animals that become stranded on beaches or are observed injured or disoriented at the sea surface. Some small species have been taken in scientific expeditions using midwater trawls. One species in the family Veliferidae inhabits shallow, nearshore waters of the Indian and Pacific Oceans. Another veliferid has been taken in bottom trawls on Pacific continental slopes and sea mounts. The remaining lampridiform families contain mesopelagic and epipelagic species that are distributed widely in temperate, subtropical, and tropical regions of all oceans except polar seas. Some species in the family Trachipteridae have somewhat restricted ranges. Radiicephalids have been collected only in the Atlantic Ocean and are extremely rare. One species of the family Lamprididae, the rare southern opah, occurs around the world in the subantarctic zone below 45° south latitude.

Habitat

Lampridiforms are strictly marine fishes. Veliferids occur at depths of 130–360 ft (40–110 m) in nearshore regions. Lampris occasionally is taken near the surface in hook-and-line fisheries off the California coast but also is known from deeper waters. Other lampridiform fishes inhabit the deep ocean, from surface waters to depths of hundreds of feet. Very little is known about the specific habitats of these species or their associations in pelagic communities.

Behavior

Observations of living specimens are extremely limited. Submersible sightings and diver observations suggest that elongate forms, such as Regalecus and trachipterids, normally orient in a vertical, head-up position and move vertically in the water column by undulating their long fin bases. In a short video of an oarfish sighted near the Bahamas, the specimen hovered almost motionless near the surface and then descended vertically and rapidly out of sight when disturbed by divers. Veliferids and lampridids swim horizontally in a typical teleost posture. Lampridids are powerful swimmers, using large pectoral fins for forward propulsion. Lampridiform fishes probably do not exhibit schooling behavior—all sightings and strandings have been of individuals. Feeding and spawning have never been observed. One regalecid, Agrostichthys parkeri, has been reported to deliver a mild electric shock when handled. Lophotus and Radiicephalus have specialized organs that empty into the cloaca and expel large quantities of a dark, squidlike ink when disturbed.

Feeding ecology and diet

Lampridiform fishes consume small planktonic crustaceans, especially euphausids; small to moderate-sized squids; and small to medium-sized fishes. These data come from anecdotal observations made of the stomach contents of single specimens. There have been no detailed studies of the feeding ecology of any lampridiform species. Very little is

known about predators of lampridiform fishes. Some species have been found in the stomachs of tunas.

Reproductive biology

Spawning has not been observed, but lampridiform fishes probably are broadcast spawners, because eggs are planktonic and have been identified for many lampridiform species in scientific collections. Eggs are large, 0.08–0.24 in (2–6 mm) in diameter, and brightly colored, usually in hues of red, pink, or amber. Incubation takes place in surface waters for approximately three weeks. At hatching, larvae have fully developed mouths and digestive tracts and begin to feed immediately on minute plankton. Larval lampridiforms are distinguished further by long, ornamented dorsal and pelvic rays. Some species, especially trachipterids, undergo abrupt metamorphosis from the larval to the juvenile form.

Conservation status

No lampridiform species are listed by the IUCN, but all are very rare. Care should be taken to ensure conservation of veliferid lampridiforms, because of their unique role in phylogenetic studies as basal taxa.

Significance to humans

Lampridiform fishes, especially the large, elongate species, attract considerable public attention when they are stranded or beached, owing to their rarity and unusual morphological features. Lampris guttatus has excellent flesh and is prized as bycatch of certain offshore fisheries. Most other lampridiform fishes are considered inedible by those who have recorded attempts to eat them.

Species accounts

List of Species

Opah

Lampris guttatus

family

Lamprididae

taxonomy

Lampris guttatus Brunnich, 1788, North Sea.

other common names

English: Moonfish, Jerusalem haddock.

physical characteristics

Large, oval, colorful species with silvery blue, iridescent body; bright red fins and snout; large eyes; and white spots covering the body and the bases of the dorsal, anal, pelvic, and caudal fins. Length typically 3.3 ft (1 m) and total weight approximately 600 lb (275 kg). Pectoral fins large and horizontally oriented. The dorsal and anal fins have elongate anterior portions, and the caudal fin is moderately forked. Superficially resembles the ocean sunfish, Mola mola, a pelagic species that is similarly large and somewhat oval but not colorful and lacks pelvic fins and a caudal fin.

distribution

All oceans, including the Mediterranean Sea, but not polar oceans. Most distribution records come from catches of pelagic longline gear set for tuna and swordfish.

habitat

Lower epipelagic zone, generally in surface waters to perhaps 1,640 ft (500 m). Analysis of data from Japanese longline fisheries shows that catches of opah increase with depth to about 920 ft (280 m) in the central and eastern Pacific Ocean.

behavior

There are no published observations of living Lampris. Swimming behavior has been inferred from the anatomical and morphological features of the pectoral fin. The massive shoulder girdle; the presence of extensive pectoral musculature, including a large red muscle mass; and the horizontal placement of the pectoral fin base suggest that the opah swims by pectoral-fin "flapping." This unusual swimming mode apparently allows the opah to swim rapidly, since it is an effective predator of active prey. Records of occurrence of opah are sporadic and widespread, suggesting that the species is a solitary wanderer in the world's oceans.

feeding ecology and diet

Predatory species that consumes squids and octopus as well as small to medium-sized fishes. Fish species eaten include hake, rockfish (Scorpaenidae), ophidiiforms, small dolphins (Coryphaena species), berycoids, argentines, and other mesopelagic species. There is one unusual report of opah feeding on small clams in shallow waters off Florida. Opah take live and cut bait on hooks as well as trolled fishing lures off the California coast. Opah can consume large quantities of prey. The stomach of one 126-lb (57-kg) specimen was found to contain 63 fishes, 8 cephalopods, and 7 crabs.

reproductive biology

Little is known of the spawning behavior, spawning seasons, or spawning habitats of Lampris. Advanced-stage oocytes removed

from the ovaries of ripe fish have a thick shell (chorion) that is amber to pink in color. Fertilized eggs are probably free floating but have not been identified in plankton collections. Only a few larval examples have been collected, all in the Atlantic Ocean. Larvae are slender and somewhat elongate initially but rapidly become deep-bodied. Pigment is confined to the head region and above the gut in the smallest specimens, but larger larvae have extensive scattered melanophores (pigmented cells) covering the entire body except the fins. The anterior rays of the dorsal and pelvic fins are elongate. Rates of mortality and growth, feeding habits, and predators of larvae are largely unknown.

conservation status

Not listed by the IUCN.

significance to humans

The species is a marketable bycatch of longline fisheries and is pursued by recreational anglers. The all-tackle game fish record is 162.9 lb (73.9 kg), and this specimen was captured off California in 1998. Its flesh is considered good, and it is thought to be excellent as a smoked product.

Crestfish

Lophotus lacepede

family

Lophotidae

taxonomy

Lophotus lacepede Giorna, 1809, type locality unknown.

The taxonomy of Lophotus is confused, and the genus is in need of revision. There is probably only one widely distributed species, but a number of nominal forms exist (L. cepedianus, L. capellei, and L. cristatus), all of which may be synonyms of L. lacepede.

other common names

English: Highbrow crestfish, inkfish, crested oarfish.

physical characteristics

The supraoccipital (a cranial bone situated above the eye) of L. lacepede bears a strong and enlarged anterior process that projects anteriorly over the forehead. This skeletal feature also is strongly developed in the crestfish's closest relative, Eumecichthys fiski, the unicornfish. The anterior process lies directly beneath the anterior dorsal fin rays and supports a large fleshy protuberance (the crest or horn) that gives the forehead of these fishes their distinct appearance. In L. lacepede the crest is thick and deep, and the forehead is either blunt or slightly projecting. In the unicornfish the fleshy protuberance is slender and greatly elongate, forming a long horn on the forehead. The body of L. lacepede is relatively long, attaining a total length of about 4.9–6.6 ft (1.5–2.0 m) and ribbon-like. Fresh specimens have been described as blackish blue, light brown, or silvery, sometimes with scattered white spots. Fins red. Dorsal fin extends the full length of the body. Caudal fin small and rounded. Pectoral fin low on body. Pelvic fins minute and located posterior to the pectoral fins. Anal fin small and located posteriorly. Possesses an elongate organ that lies above the lower intestine and produces thick, black, squidlike ink that is discharged through the cloaca. The unicornfish apparently does not possess this trait, although the ink gland is found in another lampridiform fish that is related closely to the lophotids, Radiicephalus elongatus.

distribution

Distributed widely in warm waters of all oceans. Specimens are rare, and most either have come from research cruises or have

been captured close to shore as stranded individuals in weakened condition.

habitat

Very little is known of the habitats of these fishes, owing to their rarity. Crestfish are apparently members of the epipelagic community and have been collected in surface waters to depths of only a few hundred feet (or meters). Some specimens have been taken in very shallow water, but they were probably dying.

behavior

Almost nothing is known of the natural behavior of this species. Crestfish probably discharge ink when frightened. A large adult specimen captured and gaffed during a research cruise expelled a copious amount of ink. Crestfish may develop this capability at a young age, since late-stage larvae possess the ink gland.

feeding ecology and diet

Apparently consume small fishes, squid, and pelagic octopus.

reproductive biology

Little is known of the spawning behavior, spawning seasons, or spawning habitats of Lophotus or its relatives. Eggs are pelagic and have been described from plankton collections in the Mediterranean Sea as relatively large, about 0.01 in (2.5 mm) in diameter, with many tiny spines covering the chorion. Early larvae have elongate dorsal and pelvic rays that bear large pigmented swellings. These rays often are damaged in capture and are absent in preserved specimens. Late larvae are sparsely pigmented and possess the internal ink gland, with the dark contents visible through the body wall. Vital rates, feeding habits, and predators of larvae are largely unknown.

conservation status

Not listed by the IUCN.

significance to humans

None known.

Oarfish

Regalecus glesne

family

Regalecidae

taxonomy

Regalecus glesne Ascanius, 1772. Most ichthyologists recognize a single species with worldwide distribution, but there are several nominal species that may be valid.

other common names

English: King of the herrings.

physical characteristics

Spectacular animals with long, slender, usually silver bodies; brillant red fins; a large, cockscomb-like plume of 6–10 anterior dorsal-fin rays; and long pelvic fins. When not damaged, the pelvic ray bears a large red swelling at its tip, from which its name is derived. Often attaining a length of 26–33 ft (8–10 m), oarfish are the longest of all bony fishes. (There are unconfirmed reports of some specimens reaching 56 ft, or 17m.) The long body gradually tapers to a point. The caudal fin (when present and not damaged) is tiny, and its rays bear small, laterally projecting spinules. No anal fin. About 400 dorsal fin rays and 150 vertebrae. Some confusion exists concerning the distinction between regalecids and their close relatives, the trachipterids or ribbonfishes. Fishes in both families are elongate, have crimson red fins, lack an anal fin, and possess laterally projecting, small spines on the individual rays of the caudal and pelvic fins. The oarfish attains a greater length, has only two pelvic rays (one very elongate and one small and splintlike) and a very elongate anterior dorsal fin, and is relatively slender. The trachipterids are shorter, have more than two pelvic rays (though pelvic rays are absent in one genus), lack the extremely elongate dorsal rays, are relatively deeperbodied, and have small spines on the lateral-line scales.

distribution

All oceans, including the Mediterranean Sea, but not polar seas. Most distribution records result from strandings of weak or dying fish in shallow water, although some fish have been captured by trawl.

habitat

Epipelagic species, normally inhabiting surface waters to depths of about 656 ft (200 m). The species is capable of occupying greater depths, however. Little is known of its specific habitat requirements or associations.

behavior

Recent sightings of live fish by divers confirm that swimming is not accomplished by rowing the pelvic fins, as one might suppose from the name oarfish. Instead, oarfish move in the water column by undulations of the dorsal fin. The natural body position is vertical, with the head up and dorsal fin rays and pelvic rays extended outward. The pelvic fin may have a sensory capability, allowing the oarfish to "taste" its surrounding habitat. Its close relative, Agrostichthys parkeri, has been reported to be electrogenic, delivering a mild shock when handled. It is unknown whether the oarfish shares this capability.

feeding ecology and diet

Apparently consumes planktonic crustaceans and small fishes, but little is known of its feeding ecology. The stomach of a 9.8-ft (3-m) oarfish stranded in shallow waters off California contained a large volume of krill (euphausids), numbering about 10,000 individuals.

reproductive biology

The spawning of oarfish has not been observed, and little is known of its spawning habits or seasons. The ovaries of a dying female, about 9.8 ft (3 m) in length, that was cast ashore on the west coast of Florida weighed 3.1 lb (1.4 kg) and contained approximately 140,000 unspawned eggs, some of which were ovulated. The female was observed in March, along with other dead male fish, presumably following a spawning occurrence. Oarfish eggs are pelagic and have been identified in plankton collections in the Mediterranean Sea and the waters off New Zealand. Eggs are large, 0.08–0.16 in (2–4 mm) in diameter, with pink to red chorions, and they contain numerous scattered oil droplets. Researchers report that eggs can take up to three weeks to incubate and that the emerging larva is highly developed at hatching, with a functional mouth and gut, a pigmented eye, and long dorsal and pelvic fin rays. Young oarfish resemble adults in most details and have been captured on research cruises in the Atlantic and Pacific Oceans. Vital rates, feeding habits, and predators of larvae are largely unknown.

conservation status

Not listed by the IUCN.

significance to humans

Sightings of the oarfish usually stir considerable public attention, but the species has no commercial value, and its flesh is reported to be unpalatable.

Resources

Books

Eschmeyer, W. N., E. S. Herald, and H. Hammann. A Field Guide to the Pacific Coast Fishes. Boston: Houghton Mifflin, 1983.

Fitch, J. E., and R. J. Lavenberg. Deep-Water Teleostean Fishes of California. Berkeley: University of California Press, 1968.

Heemstra, P. C. "Order Lampridiformes." In Smiths' Sea Fishes, edited by M. M. Smith and P. C. Heemstra. Johannesburg, South Africa: MacMillan South Africa, 1986.

Periodicals

Olney, J. E., G. D. Johnson, and C. C. Baldwin. "Phylogeny of Lampridiform Fishes." Bulletin of Marine Science 52 (1993): 137–169.

Patterson, C. "An Overview of the Early Fossil Record of Acanthomorphs." Bulletin of Marine Science 52 (1993): 29–59.

Saloman, C. H., M. A. Moe, and J. L. Taylor. "Observations on a Female Oarfish (Regalecus glesne)." Florida Scientists 36(1973): 187–189.

Skerry, B. "Eye-to-Eye with the Sea Serpent: First Photos of the Mysterious Oarfish." Sport Diver 5, no. 4 (August 1997): 40–43.

Sorbini, C., and L. Sorbini. "The Cretaceous Fishes of Nardo. 100. Nardovelifer altipinnis, gen. nov. et spec. nov. (Teleostei, Lampridiformes, Veliferidae)." Museo Civico di Storia Naturale di Verona, Studi e Ricerche sui Giamenti Terziari do Bolca 8 (1999): 11–27.

Wiley, E. O., G. D. Johnson, and W. W. Dimmick. "The Phylogenetic Relationships of Lampridiform Fishes (Teleostei: Acanthomorpha), Based on a Total-Evidence Analysis of Morphological and Molecular Data." Molecular Phylogenetics and Evolution 10 (1998): 417–425.

John E. Olney, PhD