scorpaeniform

Introduction

also called  mail-cheeked fish,  

      any member of the order Scorpaeniformes, a group of bony fishes that includes the sea robins, sculpins, and numerous other forms. They are characterized by a plate of bone running across each cheek.

      The scorpaeniforms are widespread throughout the oceans of the world. They are believed to have originated in warm marine waters but have invaded temperate and even Arctic and Antarctic seas as well as freshwaters of the Northern Hemisphere. The scorpaeniforms are a highly successful biological group, occurring in the sea from the midlittoral (coastal) zone down to depths of at least 4,000 metres (about 13,000 feet). They inhabit some deep freshwater lakes but are more abundant in cold streams and rivers.

 The scorpaeniforms are often divided into six suborders, only two of which have more than one family; these are the Scorpaenoidei (three families) and the Cottoidei (seven families). The best known groups are the scorpion fishes (scorpion fish) and rockfishes (family Scorpaenidae); sea robins (sea robin), or gurnards (Triglidae); flatheads (flathead) (Platycephalidae); and sculpins (sculpin) (Cottidae). The flying gurnards (flying gurnard) (Dactylopteridae; see photograph—>), considered by some authorities to belong in this order but more often separated in the order Dactylopteriformes, are treated here for convenience.

General features

      Many members are locally important commercial fish (commercial fishing). Thus the redfishes of the genera Sebastes and Sebastodes of the North Atlantic and Pacific have considerable value to the fishing industries of Europe, Russia, and North America; the flatheads are exploited in a wide area of the Indo-Pacific region, and greenlings (greenling) (Hexagrammidae) are of commercial importance in the northwestern Pacific. In general, the fishery value of the group as a whole has a greater potential than is shown by the present actual utilization by man.

      Members of the order Scorpaeniformes are not large fishes. Some of the deepwater species, such as the redfishes (redfish), grow to a length of 90 centimetres (three feet), but the majority attain a maximum length of around 30 centimetres (one foot). Externally, scorpaeniforms vary greatly; most are like the Perciformes in general appearance—i.e., they are typical, scaled, spiny-rayed fishes—but the lumpfishes (lumpsucker) (Cyclopteridae) among them are obese, often jellylike, and usually scaleless and lack sharp fin spines. Body armour is often well developed, however, and most scorpaeniforms are well equipped with spines.

Natural history

Ecology

      The greatest diversity of scorpaeniform fishes, especially among members of the family Scorpaenidae, is found in warm tropical seas. The order is particularly well represented in the shallow waters of the continental shelf. In the tropics many scorpaenids are found in association with coral; elsewhere most are found on rocky or rough bottoms. In both cases they are highly camouflaged to match their backgrounds. The sculpins, flatheads, and scorpaenids, although not fast or powerful swimmers, feed on many more active smaller fishes and crustaceans, usually capturing prey by a swift pounce using the large pectoral fins as auxiliary power units.

      Cryptic (concealing) coloration is probably best exemplified by the stonefishes (stonefish) (Synanceja), inhabitants of shallow waters, including estuaries, mud flats, coral reefs, and coral sand pools of much of the tropical Indo-Pacific. Looking like a lump of eroded coral or rock, the stonefish's body is concealed by the cragginess of its outline and by its coloration, which exactly matches that of the background. A stonefish is perfectly hidden and makes no movement until prodded with a stick or, more often, until it is stepped on, at which time it erects its dorsal fin spines. Each spine has a pair of large gray-brown fusiform venom glands, one on each side. The spines inflict puncture wounds into which a considerable quantity of venom is injected through a channel on each side of the spine. Intense pain at the site of the puncture is instantaneous and radiates within minutes to involve the whole of the affected limb. Death occasionally occurs, and secondary infections are common.

      Many other scorpaeniforms can inflict severe wounds with their fin spines or head spines, but relatively few species are equipped with venom glands. One group of venomous species includes the turkey fishes (lion-fish) (Pterois and related genera), also known as lion fishes or fire-fishes. Widespread in tropical Indo-Pacific waters, they are beautifully and boldly coloured, with patterns of contrasting stripes on the head and body that are specific for individual species and extremely long dorsal and pectoral fins. All of these fishes have long, needlelike dorsal spines with glandular venom-producing tissue and shallow channels capable of inflicting very painful but rarely fatal punctures. The bold and distinctive colouring of the turkey fish is clearly a warning, for, unlike most scorpaenids, it does not hide but boldly swims in open water around the coral heads. If disturbed, the turkey fish displays (display behaviour) by spreading its fins to their fullest extent, rotating until it assumes a position, often head down, with its dorsal spines pointing toward the intruder. If an attacker is not intimidated by this display, the turkey fish moves toward the attacker with its dorsal spines erect.

      The flatheads (Platycephalidae) are found in the same oceans as the scorpaenids but mainly in sandy, muddy, or estuarine areas. Their greatly flattened bodies are clearly an adaptation to bottom life; indeed, they bury themselves on the bottom, leaving only the eyes exposed. Many species feed mainly on small fishes, but others, like the dusky flathead (Platycephalus fuscus), the largest and commercially most valuable of the Australian flatheads, have a varied diet of fishes, mollusks, crustaceans, and marine worms.

      The sea robins (sea robin) (Triglidae) are bottom-living fishes of wide distribution. The lower two or three pectoral fin rays, which are long, thickened, and detached from the remainder of the fin, form organs of taste and touch and are used for locomotion. These rays are very mobile, and an active sea robin can move slowly along the bottom apparently supported on the rays, which continuously explore the ground ahead and on either side. The diet of most of these fish consists of crustaceans, mollusks, and other fishes, many of which burrow in the seabed.

      The most abundant littoral (shore) scorpaeniforms are the sculpins (Cottidae), significantly the only group found in fresh water, other than the closely related families Cottocomephoridae and Comephoridae. Some members of the families Scorpaenidae and Cyclopteridae are also littoral fishes. The littoral sculpins are generally small, inhabiting densely weeded pools or crevices in rocks. Both the sculpins and cyclopterids found along the shore are strongly thigmotactic (attracted to surfaces), pressing as much of their bodies to the surface as possible. The cyclopterids have well-developed sucker disks, which are derived from the pelvic fin complex. The suckers, which are effective in resisting wave action, are capable of exerting considerable force; in one instance, a force of 13.3 kilograms (approximately 29 pounds 5 ounces) was required to break the hold of an adult lumpsucker (Cyclopterus lumpus). The European littoral sea snail (Liparis montagui) can vary the suction exerted by its sucker as necessary to adjust for the speed of passing water currents.

      The cyclopterids have adopted a wide variety of lifestyles in addition to the littoral habit. The genus Nectoliparis is pelagic (i.e., inhabiting open water); members of the genera Paraliparis and Rhodichthys, of the North Pacific and Arctic Oceans, are bathypelagic, at least for a large part of their lives. In fishes found at depths of 2,400 metres (7,900 feet), the pelvic sucker disk is completely absent. In the semitransparent but beautifully pink-tinged species of the genus Careproctus, found in deep, cold polar waters, the pelvic sucker is greatly reduced in size and presumably in efficiency.

      In contrast to the cyclopterids, the greenlings are pelagic fishes that adopt a benthic (bottom) life only during the spawning season. One of the best-known members, the Atka mackerel (Pleurogrammus monopterygius), which is common in the North Pacific and has considerable sporting and commercial fishing value, spends the major part of its life in the open sea. The related yellow-fish (P. azonus) has been observed in the upper layers of the ocean in calm weather and is usually captured in purse seines. At night it descends to the bottom.

      The scorpaeniforms have adapted particularly well to fresh water. The members of the sculpin family (Cottidae) are widely distributed in the Northern Hemisphere, reaching their greatest diversity in North America and decreasing in number westward through the Eurasian landmass. In extreme western Europe there is only one species, the miller's thumb (Cottus gobio). Two endemic forms, C. kneri and C. kessleri, both of some commercial importance, are found in Lake Baikal (Baikal, Lake), Russia, and its tributary rivers. These species share Lake Baikal with a number of other species belonging to the related families Cottocomephoridae and Comephoridae. The sculpins in Lake Baikal have become adapted to exploit all of the living space offered by this inland sea. The family Cottocomephoridae is divided into eight genera and numerous species. Although many of the benthic species are restricted to a particular type of bottom and are found only within a certain depth range, most migrate into coastal waters in the spring and remain there during the warm season. Some species, however, remain in deep water all year; others, which are primarily pelagic fishes, use the bottom only to spawn.

      The two members of the family Comephoridae, called Baikal cods (Comephorus baicalensis and C. dybowskii), are pelagic fishes, the latter living at depths to 1,000 metres (more than 3,000 feet). The feeding habits of these Baikal cottoid fishes all exploit potential food resources; the pelagic species feed mainly on various pelagic crustaceans and make daily vertical migrations accompanying their prey, and the benthic forms feed chiefly on certain species of benthic copepod crustaceans. The diet of one inshore species, Batrachocottus nikolskii, however, is mainly chironomid and caddisfly larvae.

Reproduction

      The mail-cheeked fishes are highly variable in their mode of reproduction. Some of the methods used by them to reproduce are noted below. In the Comephoridae there is a remarkable imbalance between the numbers of each sex, the proportion of males in the total population being as low as 3 or 4 percent. The biological basis for this imbalance is unknown. Members of this family are viviparous (live-bearing). The females come near the surface to give birth to their young; the males remain at their normal depths. By contrast, the remaining cottoids are oviparous (egg-laying), including the Cottocomephoridae of Lake Baikal. The females of most of the latter family deposit their eggs in shallow coastal water, then leave the males to guard them until they hatch. This is also the general rule among the sculpins, in which the males guard the eggs. In some species the eggs are shed loosely and adhere to the bottom, but little reliable evidence is available concerning the breeding habits of most cottoid fishes. The northern Atlantic short-horned sculpin, or bullrout (Myoxocephalus scorpius), is known to build a rudimentary nest guarded by the male, as does the freshwater European miller's thumb. The males of these and other cottids have a well-developed structure called a urogenital papilla, which some authorities have suggested is used to introduce sperm into the female. Many cottoid species develop pronounced breeding coloration with sexual differences that apparently aid in recognition between the sexes and in territorial behaviour.

      Some members of the family Cyclopteridae build nests that are guarded by the male. The familiar lumpsucker, or sea hen (Cyclopterus lumpus), common on both sides of the North Atlantic, spawns along the coast in the winter. At least some of the inshore species, such as the striped sea snail (Liparis liparis), which has a distribution similar to that of the lumpfish, deposit their spawn in clumps on hydroids (e.g., sea moss) and seaweeds, but there is no evidence of parental care. The females of some North Pacific cyclopterids (e.g., Careproctus sinensis) have a long specialized structure (ovipositor) by which they lay their eggs under the shell of the Kamchatka crab. In general, however, little is known about the breeding biology of these fish.

      In contrast to the rather specialized reproductive behaviour of the sculpins and the sea snails, the sea robins produce eggs that are simply shed in batches in the open sea. So far as is known, no special breeding behaviour accompanies spawning except that these noisy fishes become increasingly loquacious during the spawning season. The members of the family Hexagrammidae (the Atka mackerel, for example) deposit one clump of eggs, often on algae in shallow water on stony bottoms; some species, however, like the lingcod (Ophiodon elongatus), care for their egg masses during incubation. The sea poachers, or pogges (Agonidae), lay relatively few eggs, often hiding them away in crevices. The eggs are relatively large, 1.5–1.9 millimetres (roughly ¹/₁₆ inch) in diameter in Agonus decagonus, a species found in the extreme North Atlantic. The European hook-nose (Agonus cataphractus) lays up to 2,400 eggs inside the hollow rhizoid (“stalk”) of the kelp Laminaria in a compact, membrane-covered mass. Incubation is prolonged, possibly as long as 12 months.

      Scorpion fishes of the family Aploactinidae similarly shed their eggs in the open sea. Members of the scorpaenid subfamily Scorpaeninae extrude eggs in gelatinous balloon-shaped masses; those in the subfamily Sebastinae have internal fertilization and are viviparous. The three groups represent the principal evolutionary stem groups of the scorpion fishes. In the North Atlantic redfish (Sebastes marinus) fertilization is internal, and the eggs develop within the oviduct of the mother. Fertilization usually takes place during February, after which the females form shoals and migrate to spots where warm bottom currents pass. The female can be said to be a living incubator; in such fishes, which live in cold northern seas, it is clearly advantageous to carry the developing young to an area in which more favourable conditions prevail. The young at birth are very immature, nevertheless, and brood size in the redfish is relatively large (up to 360,000); the larvae must survive a lengthy planktonic life. A smaller, shallower water redfish, the Norway haddock (Sebastes viviparus) produces much smaller broods, with brood sizes ranging from 12,000 to 30,000 young. The scorpaeniforms are distinguishable among viviparous teleosts (advanced bony fishes) by their comparatively high fecundity; comparison with many other marine fishes, single individuals of which produce millions of freely shed eggs, however, illustrates the relative advantage, at least in numbers, of bearing living young over laying eggs.

      The North Pacific redfishes or rockfishes (e.g., Sebastodes, Sebastiscus, and Hosukius) closely resemble the North Atlantic sebastine species in their reproductive biology; all species studied have been found to have relatively large brood sizes. The sebastine rosefishes (Helicolenus), found in both the northern Atlantic and Pacific Oceans, have morphological affinities with the subfamily Scorpaeninae. Studies of their reproductive biology have shown that the sebastine rosefishes have intraovarian embryos embedded in a gelatinous matrix, and they thus appear to combine sebastine viviparity with scorpaenine egg masses.

Sound production

      Since the time of Aristotle, the sea robins have been known as sound-producing fishes, and their sonic performances and mechanisms are well known. They have a large swim bladder loosely attached to the dorsal wall of the body cavity; the swim bladder is vibrated by lateral muscles in which the striated fibres run at right angles to the muscles' length. The sea robin of the North Amerian Atlantic coast (Prionotus carolinus) produces single vibrant barks and growls, as wells as series of rapid clucks with very little provocation. Some of the sculpins (Cottidae) produce dull groans and growls; it is believed that these sounds are mechanical in origin, arising from contractions of the muscles that produce periodic movements of the pectoral girdle. Flying gurnards (Dactylopteridae) are similar to the triglids in their sonic mechanism and sound production capacity.

Form and function

General features

      Many mail-cheeked fishes, such as the rockfishes, have simple fusiform (spindle-shaped) body plans, but others, such as some sea poachers, are extremely slender. Most scorpaenids, triglids, and cottids have two dorsal fins (sometimes joined), the forward one supported by stiff spines. In general, the dorsal, anal, and pectoral fins are large, sometimes strikingly so, but in some groups (e.g., cyclopterids) the spinous dorsal fin is reduced or absent.

      The one feature diagnostic of the order is the presence of a bony bar, or stay, beneath the eye, an extension of the second infraorbital bone. It is small and inconspicuous in some primitive scorpaeniforms and secondarily reduced in some specialized forms; in others, however, it is readily evident. Often it has become externally prominent, bearing protrusions or spines, or has expanded and fused other cranial bones bones to form a hard armour.

Camouflage and coloration

      Many scorpaeniform fishes, such as scorpion fishes, rockfishes, and sculpins, which live on coral or rocky bottoms, possess a remarkable degree of cryptic (concealing) coloration and shape. Numerous fleshy lappets adorn the head, fin membranes, and body scales, rendering the fish virtually invisible against a background of rocks covered with marine organisms. The effectiveness of this camouflage cannot be appreciated unless the fish is viewed in its natural habitat.

      Some members of the order, such as the sea robins, are notable for brilliant colours, especially reds. The large pectoral fins are often strikingly coloured; in the European tub gurnard (Trigla lucerna) they have spots of bright green and peacock blue. The spots on the pectorals of the flying gurnards resemble eyes and apparently function to startle and frighten potential predators when the fins are suddenly spread. The brightly coloured fins of some sea robins may function in a similar manner.

Classification

Annotated classification

      The following classification is modified from that suggested by British ichthyologist P.H. Greenwood and the Americans S.H. Weitzman, D.E. Rosen, and G.S. Myers.

Order Scorpaeniformes (mail-cheeked fishes)

 Spiny-finned fishes generally with stout bodies. Second infraorbital bone united with the preopercular to form a rigid stay across the cheek. Pelvic fins thoracic in location (sometimes modified into sucker disks), the bones directly attached to cleithra (bones like the collarbones of higher vertebrates).

      Suborder Scorpaenoidei

 Moderate-sized fishes with 24 to 40 vertebrae. Anterior ribs absent or sessile (rigidly attached). Numerous species.

      Family Scorpaenidae (scorpion fishes and redfishes)

 Paleocene to present. Marine fishes widely distributed in tropical, temperate, and northern seas. Perchlike appearance, dorsal fin spines long and numerous; head spiny, body scaly. Locally important food fishes, some with venom glands on fin spines. Size to around 100 cm (39 in.).

      Family Triglidae (gurnards and sea robins)

 Upper Eocene to present. Marine fishes of warm and temperate seas. Characterized by rather slender form, body with small scales or bony plates; head heavily armoured. Lower pectoral fin rays separate, forming a tactile organ. Locally exploited by man as food. Size to around 70 cm (28 in.).

      Family Synancejidae (stonefish)

 Tropical Indo-Pacific. Scaleless, body covered with warty tubercles. Venom glands on fin spines; dangerously venomous. Size to around 60 cm (24 in.).

      Families Aploactinidae, Pataecidae, and Caracanthidae

 Tropical Pacific, often in coral. Small scaleless fishes (except Caracanthidae, which have dense dermal papillae). Size to about 25 cm (10 in.).

      Suborder Hexagrammoidei

 Moderate-sized, slender-bodied fishes. Vertebrae 42–64. Ribs attached to strong parapophyses (projections of vertebrae). Few species, midwater and benthic.

      Families Hexagrammidae, Anoplopomatidae, and Zaniolepididae

 Northern Pacific. Small scales, long dorsal fins, spines on the head few, powerful teeth in jaws. Locally important food fishes, some with sporting value. Size of most Hexagrammidae (greenlings), Anoplopomatidae (skilfish), and Zaniolepididae (comb fishes) to about 45 cm (18 in.), some longer.

      Suborder Platycephaloidei

 Moderate-sized with head and anterior part of body strongly flattened. Vertebrae about 27. No air bladder.

      Family Platycephalidae (flatheads)

 Head and body flattened anteriorly. Marine; usually buried in soft bottom, some forms on coral; Indo-Pacific and tropical eastern Atlantic. Important commercial fishes in Southeast Asia, tropical Australia, and elsewhere. Size to 130 cm (52 in.) and 15 kilograms (33 pounds).

      Suborder Hoplichthyoidei

 Small fishes, with very depressed bodies. Scaleless, but body with bony plates. Head with heavy spiny ridges.

      Family Hoplichthyidae

 Found in moderately deep water in Indo-Pacific region. Size to 25 cm (10 in.).

      Suborder Congiopodoidei

 Moderate-sized fishes with angular bodies and well-developed dorsal fin spines. Scaleless, but sometimes rough skins.

      Family Congiopodidae (horse fishes)

 In moderately deep cold waters of Southern Hemisphere, off South America, Australia, and South Africa. Size to 75 cm (30 in.).

      Suborder Cottoidei

 Small to moderate fishes. Marine, from temperate to polar seas, and freshwater in Northern Hemisphere. Mostly without scales; many with spiny skins, others with bony plates. Many species.

      Family Cottidae (sculpins and bullheads)

 Oligocene to present. Generally large headed, with well-developed head spines. Marine and freshwater of the Northern Hemisphere (1 genus said to occur in the Tasman Sea). Mostly small, some up to 60 cm (24 in.).

      Families Cottocomephoridae and Comephoridae

 Similar to cottids but postcleithral bones absent or rudimentary. Freshwater, endemic to Lake Baikal, Russia. Size to about 16 cm (6 in.).

      Family Icelidae (two-horn sculpins)

 Head large, laterally compressed, and with small spines. Lateral line and dorsal fin base with scutes (plates). Small benthic fishes mainly of North Pacific, a few in the North Atlantic. Size to 25 cm (10 in.).

      Family Normanichthyidae

 Head and body with ctenoid (fringed) scales; head without spines. Two well-separated dorsal fins, soft fin rays branched. Marine waters off Chile. Size to 11 cm (4 in.). Probably does not belong in order Scorpaeniformes.

      Family Cottunculidae

 Body covered in loose skin covered with bony tubercles. Head large, lacking spines. Deep waters of the Arctic and North Atlantic oceans, Indian Ocean off South Africa, and Flores Sea, Indonesia. Size to 20 cm (8 in.).

      Family Agonidae (poachers and pogges)

 Eocene to present. Body covered in hard armour of large scutes. One or two dorsal fins. Teeth minute. Small, benthic, coastal fishes of northern Pacific, Atlantic, and Arctic oceans and Antarctic waters. Size to 30 cm (12 in.).

      Family Cyclopteridae (lumpfishes and sea snails)

 Body short, thick, tadpole-shaped. Skin thick, naked or with bony tubercles or small thorns. Two dorsal fins, the first often minute or modified. Pelvic fins forming a sucker disk or absent. Marine, from littoral to abyssal depths (4,000 metres) in northern Atlantic and Pacific oceans, Arctic and Antarctic waters. Size to 60 cm (24 in.); 5.5 kg (12 lb).

Order Dactylopteriformes

 Resemble Triglidae. Head covered by bony plates that are expanded into huge shields. First infraorbital bone connected to preoperculum. Pectoral rays long, numerous, and brightly coloured.

      Family Dactylopteridae (flying gurnards)

 Tropical and warm temperate regions of Atlantic and Indo-Pacific oceans. Few species. Size to 50 cm (20 in.).

Critical appraisal

      The classification of the scorpaeniforms cannot be said to have approached a final synthesis. It has been suggested that they are an aggregation of three distinct evolutionary lines, the two dominant elements being the scorpaenid and cottid-hexagrammid lines, the third, and minor, group being the anoplopomatids. On the other hand, British ichthyologist P.H. Greenwood and colleagues have pointed out that all members of the order, as recognized here, share a distinctive type of caudal (tail) skeleton. The order Scorpaeniformes is clearly related to Perciformes within a superorder Acanthopterygii.

      The systematic positions of some groups remain open to doubt. The flying gurnards have been placed by some workers in the Scorpaeniformes, and, indeed, the morphological and biological resemblance of the flying gurnards to members of the Triglidae suggests that such placement best expresses their phyletic affinities.

Alwyne Wheeler

Additional Reading

Most of the information on the scorpaeniform fishes is found in short technical articles in scientific journals. The following works are broad in nature but contain substantial information on members of this order. E.S. Herald, Living Fishes of the World (1961, reprinted 1972), is a well-illustrated book for the general reader; N.B. Marshall, The Life of Fishes (1965), contains some sections on the biology of scorpaeniforms; G.V. Nikolskii, Special Ichthyology, 2nd rev. ed. (1961; trans. of the 2nd Russian ed. of 1954), deals especially with species commercially important in the former Soviet Union; B.W. Halstead, Poisonous and Venomous Marine Animals of the World, vol. 3 (1970), provides information on the venom of these fishes and its effects. P.H. Greenwood et al., “Phyletic Studies of Teleostean Fishes, with a Provisional Classification of Living Forms,” Bull. Am. Mus. Nat. Hist., 131: 339–455 (1966); and C.T. Regan, “The Osteology and Classification of the Teleostean Fishes of the Order Scleroparei,” Ann. Mag. Nat. Hist., Series 8, 11:169–184 (1913), are rather technical, but important, contributions to the study of the scorpaeniforms.

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