Weeverfishes and relatives

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Class Actinopterygii Order Perciformes Suborder Trachinoidei Number of families 13

Photo: A four-spined sandperch (Parapercis tetra-cantha) in the Balayan Bay of Luzon Island in the Philippines. (Photo by Fred McMonnaughey/Photo Researchers. Reproduced by permission.)

Photo: A four-spined sandperch (Parapercis tetra-cantha) in the Balayan Bay of Luzon Island in the Philippines. (Photo by Fred McMonnaughey/Photo Researchers. Reproduced by permission.)

Evolution and systematics

A group of fishes referred to as the "trachinoids" was recognized in 1860 and has undergone significant modification over the years, with several groups variously added or subtracted and then added again. The current notion of the Trachinoidei actually is quite similar to that of 150 years ago, although a few groups have been put in the group that were not described at that time. The Trachinoidei is almost certainly an unnatural grouping of fishes, meaning that there is little evidence to suggest that its included families are related more closely to each other than they might be to any perci-form family outside the trachinoids. Pietsch, and then Pietsch and Zabetian, offered the first comprehensive modern phy-logenetic studies of relationships within the suborder. They did not include Pholidichthyidae and Trichodontidae in their surveys, considering the examined taxa to represent "the core of, but not necessarily to delimit," the suborder. Their results, listed sequentially in phylogenetic order (with each group being the sister to all remaining taxa) were as follows: i) Cheimarrichthyidae; ii) Pinguipedidae; iii) Percophidae, Trichonotidae, and Creediidae; iv) Champsodontidae and Chiasmodontidae; v) Leptoscopidae; vi) Ammodytidae; vii) Trachinidae; and viii) Uranoscopidae.

Johnson, and later Mooi and Johnson, reexamined much of the data and determined that many of the features used to define trachinoid relationships by Pietsch and Zabetian are distributed widely among many perciforms and do not necessarily indicate close affinity. The families themselves seem to be natural groups, except the Percophidae. In this grouping, the members of the percophid subfamily Hemerocoeti-nae exhibit derived features of the suspensorium, indicating a phylogenetic relationship with the Creediidae and Tri-

chonotidae to the exclusion of the percophid subfamilies Per-cophinae and Bembropinae. Mooi and Johnson refuted any close relationship between Champsodontidae and Chiasmod-ontidae, suggesting that the former more likely has relatives among the Scorpaeniformes and that relatives of the remaining trachinoid families might be searched for more fruitfully among other perciforms rather than among themselves. Mooi and Johnson hinted that trichodontids might be scorpaeni-forms, but Nazarkin and Voskoboinikova suggested a new suborder for the family, emphasizing its differences from other trachinoids but not resolving its enigmatic phylogenetic position. McDowall maintained that the monotypic Cheimar-richthyidae should be considered a member of the Pingui-pedidae. The relationships of the Pholidichthyidae also are unclear.

The fossil record of trachinoids is scant. A member of the Trachinidae is described from the base of the Middle Eocene from Monte Bolca, Italy (about 49 million years ago, or mya). Reported from the Agnev Formation (Upper Miocene, about 10 mya) of Sakhalin Island, Russia, are a species of Tri-chodontidae and a species put in a new family, the Trispinaci-dae, which is considered to be related to the Pinguipedidae.

There are 13 families with 235+ species in 53 genera: Ammodytidae (seven genera, 27 species), Champsodontidae (one genus, 13 species), Cheimarrichthyidae (monotypic), Chias-modontidae (four genera, 15+ species), Creediidae (seven genera, 16+ species), Leptoscopidae (three genera, five species), Percophidae (11 genera, 44 species), Pholidichthyidae (one genus, two species), Pinguipedidae (five genera, 50 species), Trachinidae (two genera, four species), Trichodontidae (two genera, two species), Trichonotidae (one genus, six species), and Uranoscopidae (eight genera, 50 species).

Physical characteristics

Not surprisingly, given that most families are not related closely, physical characteristics vary considerably among tra-chinoids. Ammodytids, the sand lances, are small to moderate sized, growing to about 16 in (40 cm). They have narrow, elongate bodies with small heads. The lower jaw protrudes beyond the upper, and there are no teeth in the jaws. These fishes have a single long dorsal fin without spines and reduced or absent pelvic fins. The body has a series of oblique folds of skin called plicae. Ammodytids swim with a distinctive eellike undulation that makes them easy to identify in the water. Champsodontids, the gapers, are small, growing only to 6 in (15 cm), but they are large-headed, with a large mouth armed with long teeth. There is a large spine on the preop-ercle and two dorsal fins, the first with four to six spines. The pectoral fin is very small, but the pelvic fin is quite large. The body is covered with spinoid, nonoverlapping scales that are raised above the body surface by a small pedicle; a series of sensory papillae can be found between the scales.

Cheimarrichthyids, the New Zealand torrentfishes, are smaller than 8 in (20 cm), with a broad, somewhat flattened, wedge-shaped head; subterminal mouth; a robust, scaled body with a long, soft dorsal fin preceded by three to five short spines; and large pectoral and pelvic fins. Chiasmodontids, the deep-sea swallowers, are moderately sized bathypelagic fishes, growing to 10 in (26 cm). They are elongate, with a large head, a large mouth with enormous teeth, a rugose head pitted with sensory pores, a scaleless body that sometimes has prickles, a large-pored lateral line, and two separate dorsal fins, the first with seven to 13 flexible spines. These fishes have a hugely distensible gut that permits them to eat prey twice their own size, giving rise to their common name. Some species bear photophores. Creediids, the sandburrowers, are the smallest trachinoids, at 1.5-3.0 in (3.5-8 cm). They are elongate, with slightly protruding eyes, a fleshy snout projecting beyond the lower jaw, and a scaled body with a single dorsal fin and reduced pelvic fins. Leptoscopids, the southern sandfishes, reach about 16 in (40 cm). They are elongate, with a broad, blunt head and small, dorsally situated eyes; a

A blue cod (Parapercis colias) near Fiordland, New Zealand. (Photo by Michael Patrick O'Neill/Photo Researchers, Inc. Reproduced by permission.)
A spotted sanddiver (Trichonotus setiger) dives head first under the sand at the first sign of danger. (Photo by David Hall/Photo Researchers, Inc. Reproduced by permission.)

dense fringe of cirri bordering the lips; a scaled body; a single dorsal fin without spines; very deep pectoral fins, and widely separated pelvic fins.

Percophids, the duckbills or flatheads, are small, reaching 12 in (30 cm), and elongate; most have a depressed head, large eyes, a scaled body, and two dorsal fins, the first with two to six spines that can be very elongate in some species. Pholidichthyids, the convict blennies, are eel-shaped and grow to 18 in (45 cm), with a rounded head, a single nostril, a scaleless body, spineless long dorsal and anal fins that are continuous with the caudal fin, and reduced pelvic fins. Pin-guipedids, the sandperches, are mostly elongate and grow to about 12 in (30 cm). They have an almost cylindrical and scaled body; a single dorsal fin with a shorter, spinous anterior portion; and large pelvic fins. Trachinids, the weever-fishes, are elongate, growing to 17 in (42 cm), with a large oblique mouth (fringed in one species), eyes situated dorsally, and a strong opercular spine with a venom gland. There are two dorsal fins; the first has five to eight strong spines, each bearing a venom gland, and the second is long and directly opposed to the equally long anal fin. The pectoral fins are large, and there are small ctenoid scales in oblique rows along the body.

Trichodontids, the sandfishes, are superficially similar to trachinids. They reach 11.8 in (30 cm), but they are scaleless and have spines on the preopercle rather than the opercle and a longer first dorsal fin with 10-15 spines. Their lips are fringed. Trichonotids, the sanddivers, have a scientific name similar to that of the previous family, which might cause confusion. They are very different fishes, in that they are very elongate and cylindrical, growing to only about 6 in (16 cm). They have a dorsal iris flap with narrow extensions resembling eyelashes, a lower jaw with a fleshy extension beyond the upper jaw, a single long dorsal fin with three to eight anterior spines that are elongate and filamentous in males of some species, fanlike pelvic fins that are larger than the pectoral fins, and a scaled body.

The protruding lower jaws or snouts of this and several other of the sanddiving families presumably facilitate substrate penetration. Uranoscopids, the stargazers, are so named because the eyes are on the top of the head and directed dor-sally, looking skyward in typical species. Stargazers, which reach 30 in (75 cm) have a squarish, bulldog-like head en cased in sculptured bones, with an almost vertical mouth having fringed lips, a heavy body with or without scales, and a prominent cleithral spine (putatively with a venom gland) just dorsal to the pectoral fin. These fishes have a single dorsal fin with up to four rudimentary spines or two dorsal fins, the first having four to five weak spines, and very large rectangular and fleshy pectoral fins. Some species have a wormlike appendage extending from the respiratory valve of the lower jaw, which is used as "bait" and some have electric organs derived from modified eye muscles, which are reported to be capable of producing 50 volts.

The color pattern varies considerably among trachinoids. Often they are pale or silvery, and they may have bars, saddles, and spots, sometimes with dark markings on the dorsal and caudal fins. Species of some families (e.g., pinguipedids, percophids, and trichonotids) exhibit sexual dichromatism as well as dimorphism. Chiasmodontids, like most bathypelagic fishes, are dark brown or black.


Ammodytidae are cold to tropical marine fish found in the Arctic, Atlantic, Indian, and Pacific Oceans and the Black, Mediterranean, and Red Seas. Champsodontidae is a marine family of the Indo-Pacific. Cheimarrichthyidae live in freshwater streams of New Zealand; the larvae are marine. Chias-modontidae are oceanic marine fishes found in the Atlantic, Indian, and Pacific Oceans. Creediidae is an Indo-West Pacific marine fish. Leptoscopidae are marine fishes found near coastal Australia and New Zealand. Percophidae are marine fishes of the Atlantic, Indian, and Pacific Oceans and the Red Sea. Pholidichthyidae are marine fishes of the Indo-West Pacific, found from coastal Philippines to northern Australia. Pinguipedidae inhabit the Atlantic, Indian, and Pacific Oceans. Trachinidae are marine fishes distributed in the northeastern Atlantic Ocean and the Mediterranean and Black Seas. Tri-chodontidae are found in the northern Pacific Ocean. Tri-chonotidae is a marine family of the Indo-West Pacific. Uranoscopidae inhabit the Atlantic, Indian, and Pacific Oceans and the Black, Mediterranean, and Red Seas. Within many of these families, particular genera and species have much more restricted distributions.


Most species are marine inshore fishes of tropical to cold temperate regions and are associated in some way with sandy to muddy substrate—sitting on it, in it, or hovering near it to dive for protection when threatened. Exceptions include the Pholidichthyidae, which live in burrows excavated under coral; the Cheimarrichthyidae, which hug the bottom of fast-flowing portions of freshwater streams; the Champsodontidae, which can be found as deep as 3,600 ft (1,100 m) and form large shoals that rise to the surface at night; and the Chi-asmodontidae, which are oceanic bathypelagic fishes found almost to 9,500 ft (2,900 m). Even uranoscopids can be found as deep as 2,300 ft (700 m) and percophids to at least 1,970 ft (600 m). Leptoscopids and uranoscopids are the only families with species that normally are found in estuaries as adults.


Most trachinoids are solitary or form loose aggregations in appropriate habitat. Ammodytids are an exception, often forming dense schools ranging from hundreds to several thousand individuals. Champsodontids also occur in large shoals. Only pinguipedids are known to be territorial. For example, Parap-ercis cylindrica is a protogynous hermaphrodite and polygynous, defending a territory of about 180 ft2 (17 m2), within which two to five females defend smaller areas. Male trichonotids have been observed displaying to each other using their long, filamentous dorsal fin spines. It is likely that hemerocoetine per-cophids, which also have elongated anterior dorsal fin spines, display in a similar manner. Several families have species that exhibit dichromatism and dimorphism, which suggests that display plays a role in communication between or among the sexes.

The activity of ammodytids is related to tidal currents and light levels; they avoid strong tidal currents and are diurnal feeders. At night they hide in sandy substrate and form large shoals during daylight hours and low current and tidal periods. European species are known to bury in the bottom during the low light intensity of northern winters. In contrast, uranoscopids and trachinids apparently move about more at night. Champsodontids exhibit diel movements, moving from the depths to the surface at night. Cheimarrichthyids may migrate to spawn, with females moving from the upper reaches to the lower reaches, where the males are, in summer or autumn. It has been suggested that some species of ammodytids migrate inshore for summer and offshore for winter months. Trichodontids move to shallow rocky shores to spawn, returning to deeper waters after the eggs are laid.

Feeding ecology and diet

All trachinoids are carnivorous, and most are piscivorous, or at least include fishes in the diet. Ammodytids and some of the smaller trachinoid families, such as Trichonotidae, feed on zooplankton or small crustaceans. Pinguipedids feed principally on small benthic crustaceans, and leptoscopids include marine worms in the diet. Uranoscopids, leptoscopids, creediids,

A well-camouflaged marbled stargazer (Uranoscopus bicinctus) lies in wait for small fish. (Photo by David Hall/Photo Researchers. Reproduced by permission.)
Two male trichonotids display to each other with their fins erect. (Illustration by Barbara Duperron)

trichonotids, and perhaps trachinids and trichodontids are sit-and-wait predators, hiding in the substrate with only the lips, the top of the head, and the eyes protruding, sucking in unsuspecting fishes and other prey.

Several families that burrow in sand have vertical mouths to facilitate upward attack and fringed lips and gill openings that are thought to prevent sand from entering their mouths and gills while they wait for prey. Uranoscopids also have nasal passages opening into the mouth cavity (which is highly unusual in fishes), permitting them to breathe without opening the mouth while buried. Some have a worm-like appendage inside the mouth that they use as a lure. One genus, Astrosco-pus, has modified eye muscles that can produce an electric shock that might be used to stun prey, though it might instead ward off predators. Pinguipedids and percophids rest on the bottom and chase down prey that is on or near the substrate. Am-modytids forage in the water column. Juvenile pholidichthyids leave their burrows in swarms to feed on plankton during the daytime, streaming back into their tunnels each night to join their parents. The adults have never been observed to leave the burrows, and their diet remains unknown. Chiasmodon-tids alternate from a chase-and-grab to a floating-trap mode of feeding. They have very large teeth and an extensible stom ach to hold on to and eat almost any prey item that they might run across in the relatively food-scarce bathypelagic habitat.

Reproductive biology

Courtship and mating information is scant for most tra-chinoids. All studied members of the pinguipedid genus Para-percis are protogynous hermaphrodites, and at least some are territorial and have harems. Males exhibit head bobbing and pectoral fanning of harem females beginning about 40 minutes before sunset. This behavior culminates in a short ascent from the bottom (less than about 3 ft, or 1 m) for spawning within half an hour after sunset. The genus spawns year-round, with peak activity in summer, a pattern characteristic of tropical species in general and likely the case for tropical representatives of other trachinoid families.

Ammodytids spawn demersal, adhesive eggs, forming clumps on sand or gravel substrate in shallow water. Eggs are not quite spherical and are small, about 0.04 in (1 mm). Females produce 1,800-22,000 eggs, which take from two to 13 weeks to hatch pelagic larvae that are 0.12-0.18 in (3-4.5 mm) long. Most ammodytid species spawn in fall and winter, though some European species spawn in spring. Trichodon-tids spawn in winter, producing 600-2,300 eggs in a gelatinous mass attached to either rocks or seaweed, depending on the species. Eggs are relatively large, about 0.14 in (3.5 mm), and yellow, taking from two months to one year to hatch large, pelagic larvae, about 0.6 in (15 mm). Cheimarrichthyids produce up to 30,000 small (about 0.02 in, or 0.6 mm), demersal eggs in rivers during late summer and fall; upon hatching larvae go to sea as part of a pelagic stage.

Champsodontids, chiasmodontids, creediids, leptoscopids, pinguipedids, and trachinids probably are broadcast spawners and produce unornamented, small (< 0.06 in, or 1.5 mm), pelagic eggs, with most shore species hatching in two to six days. The newly hatched pelagic larvae are 0.08-0.18 in (2-4.5 mm) long. Uranoscopids also have pelagic eggs, but they are unusually large (up to 0.1 in, or 2.5 mm); at least some are ornamented with a polygonal network, perhaps helping to maintain the eggs in the water column. Both trachinids and northern representatives of uranoscopids spawn in the spring and summer. Eggs are unknown for the Percophidae, Pho-lidichthyidae, and Trichonotidae.

Trachinoid larvae can be quite distinctive. Most chias-modontid larvae bear tiny spicules, whereas one genus, Kali, has a unique "gargaropteron" stage, with a large head, oversized pectoral and pelvic fins, and no spicules. Champsodon-tid larvae have extensive head spination and bear an elongate and narrow opercular appendage that can be as much as 40% of the body length, until it gradually shortens and is resorbed by the time the fish grows to about 0.4 in (10 mm). At least one species of trachinids, Echiichthys vipera, has large preop-ercular spines and large, heavily pigmented pelvic fins. Pho-lidichthyid larvae and small juveniles (less than 12 in, or 30 cm) are strikingly colored with black and white stripes. They live in burrows with the parents at night, where they attach to the ceiling and hang motionless from mucous strands secreted by the four glands on top of their heads.

Conservation status

Several species and even families have restricted ranges and exhibit considerable endemism. Many species within families are considered common, in that they are encountered frequently, but population estimates are unknown, except for some species of ammodytids. Although several species are known only from a few specimens, this is generally thought to be due to collecting artifact (difficulty of surveying habitats and so forth) rather than necessarily reflecting actual rarity. No trachinoids are considered endangered, although populations of ammodytids and the trichodontid Arctoscopus are monitored because of their commercial importance. The latter experienced overfishing in parts of Japan and had not recovered by 2000.

Significance to humans

Only a few trachinoids are targets for fisheries. Ammodytids are the basis of an important fishery in the North Sea and Japan. Total catch for the multinational North Sea fishery averaged almost 937,000 tons (850,000 metric tons) per year over the years 1996-2000, but this figure fluctuated quite widely and has been more than one million tonnes in a single season. This is an industrial fishery producing fishmeal and oil. Am-modytids are a food fish in Japan, marketed fresh or dried, averaging about 110,000 tons (100,000 metric tons) per year from 1995 to 1999. There is no major fishery for ammodytids in North America, though a minor bait fishery exists in New England, landing only about 22 tons (20 metric tons).

In addition, ammodytids have an indirect impact on humans, as they are important forage fish for seabirds, marine mammals, and other fishes, acting as intermediaries in the food chain by feeding on zooplankton and providing energy to higher predators. Fluctuations in seabird populations in the North Sea appear to be correlated with changes in ammodytid availability, and the abundance of sand lances as a forage fish has implications for such fishery species as mackerel and yellowtail flounder. Similarly, champsodontids are thought to be important forage fishes for commercial species. The dry, but tasty flesh of the greater weever (Trachinus draco) is esteemed highly in southern Europe, where it is taken commercially in small quantities; the venomous glands of its spines apparently have discouraged a large fishery. The trichodon-tid Arctoscopus japonicus supports an important commercial fishery as a food fish in Japan. Colloquially, the Japanese name is kaminarino, the "thunderfish," referring to its appearance inshore for spawning in late November, when thunderstorms are a common phenomenon in the northern areas where it occurs.

It has been suggested that the common name of the Tra-chinidae, weeverfishes, derives from the Anglo-Saxon word wivere, meaning "viper." Their severe toxicity has been known for at least 2,400 years, since the time of Apollodorus of Alexandria, who is said to have written a book on stinging and biting animals. Modern study has shown that trachinids have grooved opercular and dorsal fin spines bearing venom glands that cause severe pain and occasionally fever, vomiting, and heart failure. Shrimpers sometimes trap trachinids as by-catch and need to handle them with care. Uranoscopids also should be avoided, as they have stout cleithral spines used with good effect for protection. These spines, too, have been reported to be associated with venom glands, but some modern researchers suggest that this association needs to be reappraised. Some uranoscopids also have electric organs and so should be treated with respect. Because members of these two families bury themselves in the sand in shallow water, they are of concern for beachgoers and swimmers, who might tread on them.

1. Lesser weever (Echiichthys vipera); 2. Northern stargazer (Astroscopus guttatus); 3. Sailfin sandfish (Arctoscopus japonicus); 4. Torrentfish (Cheimarrichthys fosteri); 5. Inshore sand lance (Ammodytes americanus). (Illustration by Barbara Duperron)

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