(Lizardfishes and relatives)
Class: Actinopterygii
Order: Aulopiformes
Number of families: 12
Evolution and systematics
The Aulopiformes have been the subject of numerous systematic revisions over the past 30 years. The most recent one, by Carole C. Baldwin and G. David Johnson, published in 1996, recognized 4 suborders, 12 families, and 43 genera. The suborders include the Synodontoidei (three families, including the lizardfishes and Bombay ducks, the latter group formerly placed in the Harpadontidae and now synonomized), the Chlorophthalmoidei (three families plus two species, Bathysauropsis gracilis and B. malayanus, with no family assignment), the Alepisauroidei (four families), and the Giganturoidei (two families plus a single species, Bathysauroides gigas, with no family assignment). The order is largely monophyletic. (Some familial relationships remain to be resolved.) It traces its ancestry to the Upper Cretaceaous period (135 million years ago). The Aulopiformes share many features with midwater and deep-sea-dwelling Myctophiformes (lanternfishes and relatives), and most species may have evolved over time from life in the pelagic realm to a bottom-dwelling existence.
Physical characteristics
The Aulopiformes are characterized by both primitive and derived or advanced characters. Examples of primitive characters include abdominal pelvic fins with 8–12 rays, the absence of fin spines, the presence of an adipose fin (a structure consisting of fatty tissue located between the dorsal fin and the caudal fin), and scales that are cycloid or rounded in shape. Derived characters include a ductless swim bladder and a maxillary bone that has been excluded from the gape of the jaw. Other characters, present in some groups, include highly modified eyes, hermaphroditism, and well-developed metamorphic stages between larval and juvenile phases. Specialized gill arches further distinguish them from the Myctophiformes. Within the order, body sizes and shapes are diverse and a function of habitat and depth distribution.
Lizardfishes (25 species within the Synodontidae) are cryptically colored, cigar-shaped bottom-dwelling fishes with large, reptilian heads, large mouths, numerous teeth, and an eye placed nearly halfway along the length of the mouth. Bombay ducks (15 species within the Synodontidae) are distinguished by a short and rather rounded snout, long pelvic and pectoral fins, and a medially placed tail lobe formed from lateral line scales. Synodontids are cryptically colored, usually in mottled shades of brown, gray, or red. The Aulopidae (about 10 species) resemble lizardfishes but possess a large dorsal fin; in males, this fin has a first dorsal fin ray that extends well beyond the others. Aulopids also have two small jawbones, the supramaxillae, located along the upper edge of the jawbone. They also are cryptically colored, primarily in shades of green, brown, gray, and red. The monotypic Pseudotrichonitidae are elongate and cylindrical in shape, with a pointed snout, a single elongate dorsal fin, and elongate pelvic fins. Body coloration is exquisite, with a series of red to orangish red patches laterally, and resembling bars when viewed from above. Yellow spots are present just above the lateral line and bordering the red patches, with rows of faint electric blue spots above and below the lateral line. The fins are pale white to clear with traces of faint iridescent blue.
The Bathysauridae (two species) also resemble lizardfishes but have curved, barbed teeth and a flattened head. Members of the Chlorophthalmidae (12 species), commonly referred to as greeneyes or cucumberfishes (allegedly because they smell like cucumber) have iridescent green or yellow eyes of various sizes. Body color varies from pale green or light brown to a mottled pattern of green, silver, white, brown, and black. The Ipnopidae (about 26 species) have pencil-shaped bodies, flat heads with tiny or poorly developed eyes, and long, thickened fin rays. Body color is variably black, bronze, brown, or dark gray, or mottled in a combination of two or more of these colors. These fishes include the tripod fishes, whose extended pelvic fin rays form two legs of a tripod (with the caudal fin forming the third leg) that allows them to perch above the abyssal bottom. Among the midwater aulopiformes are the large lancetfishes (two species within Alepisauridae), which are distinguished by a long, sail-like dorsal fin that stretches from the head nearly to the adipose fin and may grow to nearly 7 ft (more than 200 cm) in length. These fishes are silvery, pale bronze, or brownish black in color, darker dorsally, and iridescent. Almost as large is the daggertooth (one species within the Anotopteridae), another midwater predator that reaches nearly 5 ft (150 cm) in length but lacks the long sail-like dorsal fin. The daggertooth lacks scales. Body color ranges from silvery to dusty with black on the tips of the pectoral fins, jaws, and also onto the caudal fin.
Also in midwater depths are the telescope fishes (Giganturidae) and pearleyes (Scopelarchidae), which have specialized tubular eyes whose form and function resemble that of a telescope (useful for detecting light in dim surroundings) and allow for forward- or upward-directed vision. Telescope fishes are generally silvery in color, while pearleyes are pale brown. Midwater and deep-water aulopiform fishes that may or may not have tubular eyes and are distinguished by fang-like teeth and a lack of scales include the sabertooth fishes (seven species within Evermannellidae) and the hammerjaw (Omosudidae, one species). The sabertooth fishes range from pale brown to black in color. Hammerjaws are translucent silvery brown, dark brown, or olive-black with hints of silver, white, and pinkish brown. Similar in shape are the waryfishes (Notosudidae), which have both scales and, uniquely, teeth on the upper jawbones or maxillae. Waryfishes are generally pale brown in color, and some species have black fins. The barracudinas (50–60 species within the Paralepididae) are slender and elongate in shape and superficially resemble barracudas; they may grow as large as 39 in (100 cm). These fishes also possess fanglike teeth; a long, pointed snout; and a dorsal fin placed midway along the body. They may or may not have scales. Body color ranges from pale brown to tan or yellowish olive.
Distribution
Members of the Aulopiformes may be found throughout the Atlantic, Pacific, and Indian Oceans, with the exception of most polar waters. They also occur in the Mediterranean, but they appear to be absent from the Black Sea. The Synodontidae typically dwell in warm, shallow waters, although at least one species is found as deep as 1,300 ft (400 m). The Bathysauridae live at depths in excess of 5,250 ft (1,600 m), whereas the Aulopidae is distributed widely, except for the eastern Pacific, in waters near shore to a depth of 3,300 ft (1,000 m). The Pseudotrichonotidae is limited to the shallow waters of Japan and the southeastern Pacific, while the Chlorophthalmidae also may be found in shallow, warm, temperate waters worldwide. Both the Ipnopidae and Giganturidae are distributed widely in deep or abyssal waters. Midwater and bathypelagic species of the families Alepisauridae, Scopelarchidae, Evenmannellidae, Omosudidae, Notosudidae, and Paralepididae all tend to be distributed widely at depths in excess of 1,625 ft (500 m), and some are found down to 3,300 ft (1,000 m). The Anotopteridae range in shallow to deep temperate waters and are rarely found in the tropics.
Habitat
With respect to patterns of habitat use, aulopiform fishes are divided neatly into two camps: bottom-dwelling and water-column or pelagic-dwelling species. Bottom-dwelling families include the Synodontidae (Bombay ducks may be secondarily pelagic), Aulopidae, Pseudotrichonotidae, Chlorophthalmidae, Bathysauridae, and the Ipnopidae. These fishes typically perch or rest upon substrates that include rubble, sand, coral, rock, algae, and even abyssal silt and mud. Some fishes, such as the synodontids, aulopids, and pseudotrichonotids, may bury themselves in sand or rubble. Pelagic families include the Alepisauridae, Anotopteridae, Scopelarchidae, Evenmannellidae, Omosudidae, Notosudidae, and Paralepididae. These fishes swim actively in the water column even at depths where light is virtually absent.
Behavior
The behavior of most aulopiform fishes is unknown. Many species live at depths that make direct observation of their behavioral patterns extremely difficult if not impossible. Generalizations about some types of behavior can be made, however. For example, bottom-dwelling species are often cryptic and have minimal movement. These characteristics allow them to ambush prey and to avoid predation. Swimming movements of these fishes often are accomplished in short bursts, followed by burying movements in the substrate. Only when they are ambushing prey or escaping predators are their swimming movements rapid. The tripodfishes, which dwell on the abyssal bottom, may "walk" along the bottom with the support of extended pelvic and caudal fins.
Fishes that swim pelagically in the midwater and deep-water realms may do so rapidly in pursuit of prey. Both lancetfishes and daggertooths are powerfully built for swimming and hunting prey. Alternately, some smaller species might hover or rest in the water column and reserve swimming for hunting prey or for vertical migrations at night. The barracudinas swim vertically, with their tails down and their heads up.
Courtship behavior has been observed for some shallow-water species. Observations of lizardfishes have revealed a repertoire of ritualized patterns, some of which also may be used in territorial displays. Among midwater and deep-dwelling species, simultaneous hermaphroditism is common, and self-fertilization is possible, thus precluding the need for courtship behavior.
Feeding ecology and diet
Aulopiform fishes are predators. Bottom-dwelling species, such as the lizardfishes and Bombay ducks, typically feed upon smaller fishes and shrimps that they ambush and capture with their large, tooth-filled mouths. These fishes may bury themselves under the substrate and ambush passing prey just above the bottom and well into the water column. Alternately, they may ambush from perched positions on corals, rocks, or other objects, or they may launch an attack while hovering above the bottom. Regardless, the ambush is executed rapidly and is remarkably successful. Midwater and deep-water pelagic species probably capture prey by hunting or, under dim light conditions, by ambushing passing fishes or larger invertebrates, such as cephalopods or crustaceans. Owing to the colder water temperatures at greater depths, the digestive processes of deep-dwelling species appear to be slow. Thus, these fishes probably feed much less frequently than their shallow-water relatives. Aulopiformes are likely preyed upon by other predatory fishes and also by toothed whales.
Reproductive biology
Members of the Aulopiformes have two mating systems, gonochorism and simultaneous hermaphroditism. Members of the suborder Synodontoidei are gonochoristic, that is, they have separate male and female sexes, and no sex change occurs. Although few detailed studies of reproduction in this suborder exist, its shallow water-dwelling members probably spawn pelagically in the water column and release gametes, which, as fertilized eggs that become larvae, drift in the water column until the larvae settle on suitable habitat and recruit to a local population as a functional member. Courtship and spawning may be seasonal and likely is affected by water temperature. Thus, at higher latitudes courtship is limited to the warmer months of the year. In the tropics, courtship and spawning may proceed all year long.
The lizardfishes mate in pairs before or just after sunset; if the local population size is relatively large and males outnumber females, an alternative tactic may be used. For example, Synodus dermatogenys employs lek-like courtship behavior during reproduction. In this system, males form mobile territories in the presence of one or more females. Then they attempt to court a female while defending courtship space around her. Females control spawning. The female may choose to spawn with a single male, or she may allow the participation of additional males who contribute a proportion of their gametes to the fertilization of the gelatinous egg mass that is produced by the female. Furthermore, and unlike most pelagic spawning species that reproduce around sunset, the female may engage in more than one spawning event during a given evening.
The female also may choose to abort a spawning ascent if she determines that too few males are participating in the ascent. By allowing multi-male spawning, the female may ensure greater fertilization success for her eggs and promote genetic diversity as well. The remaining suborders appear to be capable of being both male and female at the same time, and they can reproduce by self-fertilization. This trait may have allowed for the radiation of species throughout the deep-water realm. Upon maturity, members of the Notosudidae leave the continental slope and spawn pelagically in the open ocean.
Conservation status
No species are listed by the IUCN.
Significance to humans
Although the flesh of shallow-water aulopiform fishes may be generally bony, some species are taken as food in both subsistence and commercial fisheries. Bombay ducks, for example, are caught in the estuaries of India and sold dried in the markets of Mumbai (Bombay), from which their common name is derived. A commercial fishery for other synodontids exists on the trawling grounds of Australia, Hong Kong, and parts of Southeast Asia (where they also are taken with monofilament nets and hook and line). Lizardfishes are sold fresh or salted or in processed form, such as fish balls, fish crackers, or fishmeal. The sergeant baker, Aulopus purpurissatus (Aulopidae), is taken by recreational fishers in Australia as well. Similarly, lancetfishes are caught accidentally on lures trolled by anglers in South African waters and elsewhere.
Species accounts
Longnose lancetfishGreeneye
Tripodfish
Slender lizardfish
Clearfin lizardfish
Painted lizardfish
Resources
Books:Allen, G. R., and R. Swainston. The Marine Fishes of North-Western Australia: A Field Guide for Anglers and Divers. Perth, Australia: Western Australian Museum, 1988.
Eichler, Dieter, and Robert F. Myers. Korallenfische Zentraler Indopazifik. Hamburg: Jahr Verlag, 1997.
Helfman, Gene S., Bruce B. Collette, and Douglas E. Facey. The Diversity of Fishes. Malden, MA: Blackwell Science, 1997.
Kuiter, Rudie H. Coastal Fishes of South-Eastern Australia. Honolulu: University of Hawaii Press, 1993.
Leis, J. M., and B. M. Carson-Ewart, eds. The Larvae of Indo-Pacific Coastal Fishes: An Identification Guide to Marine Fish Larvae. Leiden, Netherlands: Brill, 2000.
Masuda, H., K. Amaoka, C. Araga, T. Uyeno, and T. Yoshino, eds. The Fishes of the Japanese Archipelago. Tokyo: Tokai University Press, 1984.
Myers, R. F. Micronesian Reef Fishes: A Field Guide for Divers and Aquarists. 3rd edition. Barrigada, Guam: Coral Graphics, 1999.
Nelson, Joseph S. Fishes of the World. 3rd edition. New York: John Wiley & Sons, 1994.
Paxton, John R., and William N. Eschmeyer, eds. Encyclopedia of Fishes. San Diego: Academic Press, 1995.
Sadovy, Y., and A. S. Cornish. Reef Fishes of Hong Kong. Hong Kong: Hong Kong University Press, 2000.
Smith, M. M., and P. C. Heemstra, eds. Smiths' Sea Fishes. Berlin: Springer-Verlag, 1986.
Thresher, R. E. Reproduction in Reef Fishes. Neptune City, NJ: T. F. H. Publications, 1984.
Periodicals:Donaldson, T. J. "Lek-like Courtship by Males and Multiple Spawnings by Females of Synodus dermatogenys (Synodontidae)." Japanese Journal of Ichthyology 36 (1990): 439–458.
Sweatman, H. P. A. "A Field Study of the Predatory Behavior and Feeding Rate of a Piscivorous Coral Reef Fish, the Lizardfish Synodus englemani." Copeia 1984 (1984): 187–194.
Organizations:IUCN/SSC Coral Reef Fishes Specialist Group. International Marinelife Alliance-University of Guam Marine Laboratory, UOG Station, Mangilao, Guam 96921 USA. Phone: (671) 735-2187. Fax: (671) 734-6767. E-mail: donaldsn@uog9.uog.edu Web site:
[Article by: Terry J. Donaldson, PhD]
