Myctophiformes

(Lanternfishes)

Class Actinopterygii

Order Myctophiformes

Number of families 2

Evolution and systematics

The earliest fossil records for the family Myctophidae are reported from the Miocene epoch of the Upper Tertiary period approximately 23 million years ago.

The current order has undergone a series of taxonomic revisions over the years. Until about 1940, the neoscopelids were included as a subfamily within the Myctophidae. Both were included as members of the order Myctophiformes (two suborders containing some 15 families), first erected in 1911. The Myctophiformes were relegated to a suborder within the Salmoniformes in the sweeping systematic revision of living teleost fishes in the mid-1960s (the original Grzimek's account of myctophids places them in that order), but this received little support. By the early 1970s, the Myctophiformes were reestablished as a separate order, with the neoscopelid and myctophid families being recognized as a distinct suborder, the Myctophoidei. An extensive re-view of the myctophoid families in the mid-1990s resulted in the establishment of a separate superorder, the Scopelomorpha, containing the order Myctophiformes. As constructed, the Myctophiformes were reduced to the families Neoscopelidae and the Myctophidae, with the other genera of the former Myctophiformes placed in a sister group, the Acanthomorpha.

As the order is currently organized, the Neoscopelidae ("blackchins") represent the more generalized morphology, and only three genera and six species are currently recognized. The Myctophidae ("lanternfishes") are believed to be derived from the neoscopelids, and are a far more diverse family of some 230 to 250 species in 32 currently recognized genera. In the most recent review of the family, two subfamilies are recognized, the Myctophinae (13 genera) and the Lampanyctinae (19 genera).

Physical characteristics

Neoscopelids and myctophids are generally small fishes, with the largest species in both families not exceeding 11.8 in (300 mm) standard length (SL, measured from tip of the snout to base of tail). Most myctophid species are much smaller, usually less than 3.1 in (80 mm) SL at maximum size. The most common members of both families resemble anchovies, with very large terminal to subterminal mouths and large eyes. In fact, in some Russian papers, myctophids are referred to as "luminescent anchovies." The jaws bear numerous tiny teeth, and in most species, the gills bear enlarged bladelike gill rakers along the first gill arch, the number of which is used as a taxonomic character for differentiating species.

Probably the most distinctive characteristic of most species of both families are the numerous light-producing organs (known as photophores) covering the body. The photophores are concentrated along the lower sides and ventral (belly) region, as well as on the head. The photophores are arranged in patterns that are distinctive to each species. In addition to photophores, many species of myctophids bear luminescent scales and glands in particular regions. The production of light in the glands and photophores is the result of a chemical oxidation reaction that can be triggered and regulated by the animal's nervous system. The light produced is in the blue-green range and in some of the glands can produce a burst of light like a camera flashbulb going off, enough to illuminate the interior of a darkened submersible!

Both families exhibit two general body morphologies among different genera and species. One is a robust, firmly muscled body, the other, a watery, flabby body with weakly developed skeletons and muscles. These body forms are believed to relate to vertical distribution and habits.

The rays of all fins are soft. An adipose fin is present in all species. Pelvic fins are forward of the mid-body, usually under the beginning of the single dorsal fin. Pectoral fins are quite variable in length among different genera, but in all cases are attached along the lower one-third of the body. In neoscopelids and some species of myctophids, the pectorals are long and sweeping, in some species extending almost the length of the body, while a number of soft-bodied species in the genus Lampanyctus have such small, delicate pectorals that they are almost unnoticeable.

The bodies are fully covered with deciduous scales, which are cycloid (smooth) in most species, although members of a few genera (most notably, Myctophum) bear ctenoid (ctenii are small toothlike structures) scales. These scales blow off the body in a glittering cloud when the fish is struck by objects such as a net, submersible, or predator. Specialized scales cover the photophores. Some scales in myctophid species are covered with a luminescent gland.

Coloration observed in living specimens ranges from a brilliant metallic bronze in the neoscopelid genus Neoscopelus to a countershaded dark blue-black on the dorsal surface and mirror-like silvery sides and ventral surfaces in most myctophid species. However, some deep-dwelling myctophid species, including members of the genus Lampanyctus and Taaningichthys, are dark brown or black. Photophores on freshly captured specimens appear silver, reddish, or in species of the genus Diaphus, deep sapphire blue.

Distribution

The neoscopelid species are mainly found in deep waters in tropical and subtropical regions. Two of the three genera have representatives found in all three oceans, but the monotypic genus Solivomer is thus far only known from deep waters off the Philippines.

In contrast, myctophids are found in all oceanic waters of the world, with endemic species occurring in all but the Arctic Ocean. In his comprehensive treatise Developments in Deep-Sea Biology, Marshall (1980) stated, "…lantern-fishes are so successful that a sizeable net towed at mesopelagic levels almost everywhere in the ocean is almost bound to catch them. If, as seems very likely, they have not colonized the Arctic Sea, then it is improbable that other groups of midwater fishes have gained a footing."

Species diversity of myctophids is highest at tropicalsubtropical latitudes, while abundances of individual species appear greatest at temperate and higher latitudes.

Habitat

Both neoscopelids and myctophids are considered oceanic, that is, they normally inhabit waters oceanward of the continental shelf edge. As adults, species of both families are primarily mesopelagic inhabitants, usually found between 660 and 3,330 ft (200 and 1,000 m). Distribution of some species (Scopelengys tristis in the Neoscopelidae, and all Taaningichthys species in the Myctophidae) may extend into the upper bathypelagic, perhaps to about 3,960 ft (1,200 m) or so. Several neoscopelid and a number of myctophid species are thought to be (or to become at some point in their lives) benthopelagic, spending part of their life cycle near, but not in contact with, the bottom.

Larval myctophids are primarily epipelagic. The few studies that have been done on their distribution shows them to mainly occur between about 165 to 825 ft (50 to 250 m) depth.

Behavior

One of the most notable behaviors observed among many mesopelagic animals, especially myctophid fishes, is that of diel vertical migration. With the exception of the deep mesopelagic genus Taaningichthys, adolescents and adults of all myctophid species move from mesopelagic depths into very shallow epipelagic waters at night. In fact, a number of species can be dip-netted from the very surface waters. They do this to feed and to lay their eggs in the food-rich shallower surface waters, usually above 330 ft (100 m) depth. Ascent and descent have been estimated to take about 2 hours each for a species population to shift from daytime to nighttime depths and vice versa.

Let us put this remarkable achievement into a human perspective. A 2-in (50-mm) myctophid migrating from 2,300 ft (700 m) to 330 ft (100 m) and back travels about 12,000 body lengths in four hours. This would be equivalent to a 6-ft (180-cm) human having to travel 72,000 ft or 13.6 mi (2.2 km) on foot in 4 hours every night.

Within any migratory population, it is believed that most individuals undertake this movement over each diel cycle. However, in most species, larvae are nonmigratory. Newly metamorphosed juveniles also have been shown to either remain shallow and nonmigratory, or to descend into deep water, after which they remain nonmigratory for a period of time. Other restrictions on migration also have been demonstrated. Researchers have shown that in some species, old individuals may restrict or cease migrating, and gravid females often reduce the extent of migration. In addition, it has been shown that physical conditions such as solar eclipses, the degree of moon fullness, clarity of the night sky and the presence of strong current boundaries all affect the extent of vertical migration.

Observed swimming behavior among myctophids takes two forms, depending on the body type. Robust-bodied species swim in short bursts, propelled by a rapid closing of the tail fin rays and flick of the tail. In general, these are the strongest migrators, with the widest difference in day and night vertical distribution. The flabby-bodied forms tend to move with a slow eel-like wriggling of the entire body. These species tend to be found in the deeper mesopelagic depths and migrate shorter distances.

Neoscopelids are not common animals, and little is known about their behavior or habits. An individual of the neoscopelid Neoscopelus microchir was observed from a submersible in a head down position with its large pectorals held straight out from the sides. It evaded the submersible by swimming downward in short bursts similar to the robust myctophid behavior and remaining in a head down posture.

Feeding ecology and diet

As with other aspects of their biology, specific feeding habits of neoscopelids are unknown.

Historically, myctophids have been characterized as opportunistic feeders with a generalized diet of small crustacean zooplankton. While it is true that almost all myctophid species can be characterized as crustacean zooplanktivores, a few detailed studies have shown that myctophids actually exhibit a high degree of size and species selectivity. Prey are consumed whole.

Post-metamorphic and adult myctophids are mainly nocturnal feeders. Indeed, a longstanding hypothesis regarding their diel migration is to enter the food-rich surface waters at night to feed. In contrast, a recent study conducted on 14 species of myctophid larvae showed that all but one species fed during the day, with one species showing no temporal response to feeding. Most larvae fed on very small crustacean zooplankton, but several species also included gelatinous zooplankton such as salps as an important or primary prey resource.

While the presence of neoscopelids as prey items of other species has rarely been reported, myctophids are important diet components for a number of different predators. Myctophids form consistent to significant prey items for a number of mesopelagic predatory fishes including many of the stomiiforms (dragonfishes, snaggletooths, and viperfishes). Squids have been observed feeding on myctophids on numerous occasions, and myctophid otoliths have been recovered from squid stomachs as well. A number of marine mammal species have been found with significant numbers of myctophid remains in their stomachs. Reported stomach contents of the beaked whale genus Mesoplodon from the western North Atlantic include large numbers of the myctophid Ceratoscopelus maderensis as well as squid remains.

Myctophids have also been reported as regular diet components for a number of oceanic seabirds, especially species that feed at night and presumably capture the myctophids as they themselves feed in shallow waters at night. One group of predatory animals in which lanternfishes are rarely reported are epipelagic fishes such as tunas (family Scombridae) and their relatives. This is because scombrids are daytime visual predators, and except for some deep diving species, such as large bluefin tuna, they are not feeding when myctophids are present in their habitat. A second hypothesis regarding the diel vertical migrations of myctophids and other mesopelagic migrators is that the migration is driven by a downward descent in daytime to avoid epipelagic predation, with a return to food-rich epipelagic waters at night for feeding and reproduction.

Reproductive biology

Neoscopelids are apparently dioecious, but beyond this, no information is available on their reproductive habits.

The myctophids are also dioecious, and a number of genera also exhibit sexual dimorphism. The type of dimorphism varies among these genera and even among populations.

In a number of genera (e.g. Benthosema, Hygophum, Myctophum), males possess a supracaudal luminescent gland (just in front of tail on the upper surface of body), while females possess an infracaudal gland (in front of tail on lower surface). In the diverse genus Diaphus, most species have enlarged luminescent glands on their heads (called supraorbital glands or "headlights"), which are typically much larger in males. Males and females of the monotypic genus Notolychnus valdiviae can be distinguished by the noticeably larger eyes of the males. Another pattern of dimorphism is found in some species such as Ceratoscopelus warmingii and Electrona antarctica, in which males are distinctly smaller than females at maximum size.

Although there are exceptions to the rule, lower latitude species tend to spawn year-round, whereas higher latitude species typically spawn during a restricted period once per year. Lower latitude species tend to live 1 year or less, whereas higher latitude species may live 3–4 years.

Conservation status

There are no known conservation measures specific to these families. No species from either family is listed by the IUCN.

Significance to humans

From a commercial standpoint, the significance of these families is minimal and mostly indirect. Several fisheries have been or are being conducted for myctophids, in particular by the former Soviet Union, Republic of South Africa, and most recently, in the Arabian Sea by Iran. Myctophid catches are mainly processed to form fish meal, which is used as poultry feed and also as a crop fertilizer. In a fashion similar to sardines and anchovies, one may purchase tins of myctophids packed in oil.

In an ecosystem sense, however, the impact of myctophids may be especially enormous. Studies show that myctophids occupy a central role in open ocean energy transfer, especially between surface and deep ocean waters. They are important prey (in some cases, the most important) for a number of marine mammals. Damage to, or loss of, myctophid populations could have serious repercussions for many other organisms in open ocean food webs.

Species accounts

List of Species

Skinnycheek lanternfish

Benthosema pterotum

family

Myctophidae

taxonomy

Scopelus pterotus Alcock, 1890, Bay of Bengal.

other common names

Japanese: Iwa-hadaka.

physical characteristics

Deep, slightly pointed head with very large eyes. Pectoral fins are moderately long, reaching to about the middle of the dorsal fin. This is one of the smaller species of lanternfishes, reaching a maximum of 2 in (50 mm) SL, although relatively few specimens of greater than 1.6 in (40 mm) have been reported. Coloration is highly reflective silver on sides and ventral surfaces, with a blue-black dorsal surface.

distribution

Found primarily in the northern Indo-Pacific region, although larval specimens have been reported in the south Atlantic off South Africa. There are also some reported specimens from the eastern Pacific near Costa Rica and El Salvador as well. It is especially abundant in the northern Indian Ocean and Arabian Sea, and is the only myctophid species captured in the Gulfs of Aden and Oman.

habitat

Oceanic, mesopelagic. It is often reported to be associated with continental shelf edges and around islands. Some studies have suggested that it is benthopelagic. Reported daytime depth ranges are between 426 and 1,640 ft (130 and 500 m), with night depth ranges from the surface to about 984 ft (300 m).

behavior

This species is a vertical migrator. It also is known to form extremely dense aggregations. Catch rates using large commercial pelagic fishing trawls have captured as much as 88 tons

(80 metric tons) per hour of fish in the northern Arabian Sea, where this species is especially abundant.

feeding ecology and diet

Crustacean zooplankton, especially copepods. There is a shift towards larger crustacean prey as the fish grow larger. Feeding occurs at night.

reproductive biology

Sexes are separate and dimorphic. Like other members of this genus, sexually mature males have a series of luminescent scales in a supracaudal position, whereas in females, the luminescent scales are infracaudal. Sexual maturity in females occurs at around 1 in (25.4 mm) SL. Release of eggs and sperm is external, and reproduction occurs in the late afternoon and evening as the animals are migrating upwards; the buoyant eggs then float into the food-rich zone while developing. Benthosema pterotum is a serial batch spawner, releasing from 200 to 3,000 eggs per batch, depending on body size. Spawning appears to continue from the onset of sexual maturity until death, with an estimated life span of slightly less than one year.

conservation status

Not threatened.

significance to humans

Benthosema pterotum is a target species for commercial capture by Iran. Plans were to use a processing vessel of 165 tons (150 metric tons)/day processing capacity to convert B. pterotum captured in the Gulf of Oman (a region of especially high density for this species) into fish meal for fertilizer. It is unknown whether these operations are still continuing.

No common name

Electrona antarctica

family

Myctophidae

taxonomy

Scopelus antarcticus Günther, 1878, Antarctic Ocean, Stations 156 and 157.

other common names

None known.

physical characteristics

The species is characterized by a relatively large, deep head, with large eyes, and a long series of photophores above the anal fin. Pectoral fins are moderately long, reaching to about the middle of the dorsal fin. It is a large species, attaining a maximum reported size of more than 4 in (101.6 mm) SL. Sides and ventral surfaces are highly reflective and silver in color, with a deep blue-black along the dorsal surface.

distribution

Considered to be endemic to Antarctic waters, although some small individuals, thought to be waifs, have been collected north of the Antarctic convergence. Considered one of the few truly polar species of myctophids.

habitat

Oceanic, mesopelagic. During daylight hours, this species resides below 1,640 to over 2,952 ft (500 to over 900 m) depth, while at night it can be found between 0 and 990 ft (0 and 300 m). During periods of 24-hour sunlight, "nighttime" depths of capture usually are more than 660 ft (200 m).

behavior

The species is a strong vertical migrator, and is known to enter the very surface waters during night hours, where it is often eaten by seabirds.

feeding ecology and diet

This species is a crustacean zooplanktivore. It feeds on copepods, ostracods, and euphausiids. Larger individuals are known to have a greater incidence of euphausiids in their diet, especially the abundant krill, Euphausia superba.

reproductive biology

Sexes are separate, and males are distinctly smaller than females at a maximum size of 3.3 in (83.8 mm), vs. 4 in (101.6 mm) SL. Although age has been estimated to be as much as 11 years, the most reliable report has suggested a maximum age of 3.5 years for this species. It is believed to attain sexual maturity in its second year. Based on the staging of oocytes in collected females, it is thought that this species has a restricted spawning period during the southern spring.

conservation status

Not threatened.

significance to humans

Of no known commercial use, but is an important link in southern ocean ecosystem dynamics.

No common name

Lepidophanes guentheri

family

Myctophidae

taxonomy

Lampanyctus güntheri Goode and Bean, 1896, based on single specimen "obtained by the Gloucester fleet."

other common names

None known.

physical characteristics

Males and females both exhibit elongated, slender bodies with relatively pointed heads. Maximum length is about 2.75 in (69.9 mm) SL. There is no apparent sexual dimorphism. In addition to body photophores, numerous luminescent scales are found along the bases of the dorsal, anal, and adipose fins, plus along the ventral region of the tail. A distinctive feature of this species is the length of the pectoral fins, which are very long, extending to the posterior end of the anal fin. Freshly preserved specimens are deep blue-black along the dorsal surface and iridescent silver along the sides and ventral region.

distribution

Confined to the Atlantic Ocean. It is one of the most abundant myctophid species in the Gulf of Mexico, and according to the comprehensive zoogeographic analysis of Atlantic myctophids by Backus et al. (1977), it is "… the ranking myctophid in the Atlantic Tropical Region."

habitat

Oceanic, mesopelagic. Lepidophanes guentheri has been reported between 1,394 and 2,460 ft (425 and 750 m) during the day and between 131 to 410 ft (40 and 125 m) at night in the tropics, but at higher latitudes (off Bermuda and in the Gulf of Mexico), its daytime and nighttime depths are usually deeper (2,296–3,300 ft, or 700–1,000 m during the day; 165–574 ft, or 50–175 m, at night). A detailed study on the Gulf of Mexico population reported nonmigration by juveniles.

behavior

Throughout its range in tropical environments, this species is a dominant component of the vertically migrating mesopelagic fauna. No other specifics of behavior are available.

feeding ecology and diet

This species is a crustacean zooplanktivore. Primary prey are copepods and at larger sizes, euphausiids. In a detailed study conducted in the eastern Gulf of Mexico, this species was one of three myctophid species that were found to remove more than 10% of the zooplankton biomass in epipelagic waters at night.

reproductive biology

Males and females are separate sexes, or dioecious. This species is a serial batch spawner, releasing from 600 to more than 2,000 eggs per batch, depending on fish size. Sexual maturity in females is attained between 1.6 and 1.8 in (40.6 and 45.7 mm) SL. Eggs are released at night when the adults are at their shallow nighttime depths. Once sexual maturity is attained, spawning is repeated continuously every few days until death. Maximum age for this species has been shown to be about 14 months in the Gulf of Mexico.

conservation status

Not threatened.

significance to humans

None known.

Resources

Books

Backus, Richard H., et al. "Atlantic Mesopelagic Zoogeography." In Fishes of the Western North Atlantic. Vol. 7, edited by Robert H. Gibbs, Jr. New Haven, CT: Sears Foundation for Marine Research, 1977.

Gartner, John V., Jr., Roy E. Crabtree, and Kenneth J. Sulak. "Feeding At Depth." In Fish Physiology. Deep-Sea Fishes. Vol. 16, edited by David Randall and Anthony Farrell. San Diego: Academic Press, 1997.

Marshall, Norman B. Developments in Deep-Sea Biology. London: Blandford Press, 1980.

Nafpaktitis, Basil G. "Family Neoscopelidae." In Fishes of the Western North Atlantic. Vol. 7, edited by Robert H. Gibbs, Jr. New Haven, CT: Sears Foundation for Marine Research, 1977.

Nafpaktitis, Basil G., et al. "Family Myctophidae." In Fishes of the Western North Atlantic. Vol. 7, edited by Robert H. Gibbs, Jr. New Haven, CT: Sears Foundation for Marine Research, 1977.

Stiassny, Melanie L.J. "Basal Ctenosquamate Relationships and the Interrelationships of the Myctophiform (Scopelomorph) Fishes." In Interrelationships of Fishes, edited by Melanie Stiassny, Lynne Parenti, and G. Johnson. San Diego: Academic Press, 1996.

Periodicals

Dalpadado, Patricia. "Reproductive Biology of the Lanternfish Benthosema pterotum from the Indian Ocean." Marine Biology 98 (1988): 307–316.

Dalpadado, Patricia, and Jakob Gjösaeter. "Feeding Ecology of the Lanternfish Benthosema pterotum from the Indian Ocean." Marine Biology 99 (1988): 555–567.

Gartner, John V., Jr. "The Life Histories of Three Species of Lanternfishes (Pisces: Myctophidae) from the Eastern Gulf of Mexico. II. Age and Growth Patterns." Marine Biology 111, no. 1 (1991): 21–28.

——. "Patterns of Reproduction in the Dominant Lanternfish Species (Pisces: Myctophidae) of the Eastern Gulf of Mexico, with a Review of Reproduction Among Tropical-Subtropical Myctophidae." Bulletin of Marine Science 52, no. 2 (1993): 721–750.

——. "Review of the Fisheries Biology of the Mesopelagic Fishes of the Northern Arabian Sea and Gulf of Oman." Food and Agriculture Organization of the United Nations Technical Report (1996): 43–60.

Gjösaeter, Jakob, and Kouichi Kawaguchi. "A Review of the World Resources of Mesopelagic Fish." Food and Agriculture Organization of the United Nations Technical Report 93 (1980): 1–151.

Greely, Teresa M, John V. Gartner, Jr., and Joseph J. Torres. "Age and Growth of Electrona antarctica (Pisces: Myctophidae), the Dominant Mesopelagic Fish of the Southern Ocean." Marine Biology 133 (1999): 145–158.

Hopkins, Thomas L., and John V. Gartner, Jr. "Resource Partitioning and Predation Impact of a Low Latitude Myctophid Community." Marine Biology 114, no. 2 (1999): 185–198.

Other

"A Global Information System on Fishes." FishBase. June 14 002 [cited Oct. 27, 2002]. <http://www.fishbase.org/home.htm>

"A Collaborative Internet Project Containing Information About Phylogeny and Biodiversity." Tree of Life Web Project. June 14, 2002 [cited Oct. 27, 2002]. <http://tolweb.org/tree>

John V. Gartner Jr., PhD