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Flatfishes, Order Pleuronectiformes, Heterosomata, Flounders and Soles family species, their habitats, characteristics, fishing methods.
Flatfishes, Order Pleuronectiformes, or Heterosomata are generally spiny-finned, deep-bodied, laterally highly compressed fishes including the halibut, plaice, turbot, and sole, all of which distinguished from other species by having both eyes on the same side of the head in juveniles and adults. In some flatfish groups, eyes are on left side (
Psettoididae, Citharidae, Bothidae,
Achiropsettidae, Scophthalmidae, Paralichthyidae and
Cynoglossidae), in others on the right side (Pleuronectidae, Samaridae, Achiridae and Soleidae).
All flatfishes begin life as pelagic, bilaterally symmetrical fishes, looking like normal fishes, which during larval growth during a few weeks, they are going through a spectacular ontogenetic change where one eye (depending upon the species either the right or left) migrates from one side of the head to the other at end of pelagic larval stage. Their bodies flatten into an oval shape, one side turns dark and one side white, and they settle to the bottom of the sea floor. This transformation (metamorphosis) occurs very rapidly. Later more changes occur from a regular symmetrical body in various external and internal structures in the skeletal and digestive systems, including placement of nostrils on the head, differential development of bones in anterior head skeleton, differences in jaw shape and dentition on either side of the body, degree of development of lateral body musculature, lateral-line development on either side of the body, differential coloration on ocular and blind sides, and differences in paired fin development on ocular and blind sides of the body. The underside of the flatfish is pale and the top is colored to match the environment; some species, especially the flounders, are able to change their pigmentation.
The flatfishes are a very homogenous tribe, so different from all other fishes by their flatness; less obvious is the fact that they do not lie on the belly but on one side, right or left.
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One of the distinguishing features of the order is the presence of protrusible eyes, one more adaptation to living on the seabed, and the extension of the dorsal fin onto the head. All of the flatfishes have a single long dorsal and anal fins on each edge, both without spines; they also have well-developed ventral fins (at least on the eyed side) which are either on the right-hand edge or on the left-hand edge as the fish lies. Most of the species have pectoral fins, one on eyed side and the other on the blind side. The ventral fins are in front of the pectorals or in line with them; the abdominal cavity is very short, and some species are armed with a stout anal spine. While one of their eye migrates around the head until both the eyes finally come to lie close together, the mouth retains its original position more nearly, so that it is often described as opening sidewise.
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Habitats
Flatfishes usually inhabit shallow, soft sediments on the continental shelf to a depth of about 200 m. Some species are found in greater depths to about 500 m or more. Flatfishes generally lie on the bottom on their blind side. They are bottom-dwelling predators, usually found either lying on top of the substratum or partially burrowing partially or almost entirely in sand or soft mud with only their eyes protruding above the substratum. They are capable of a rapid change in coloration which allows them to match their background almost perfectly. Flatfishes are found on a variety of substrata including silt, mud, sand and sand–shell mixtures, with some species also occurring on rocky or pebbly bottoms. Some species appear to have strong preferences for particular substrata, whereas others are found on a variety of bottom types.
Most flatfishes appear to feed on or near the bottom, but some of the larger species will rise off the bottom to capture prey. Most occur in shallow water, although some species also occur at slope depths.
Reproduction
A flatfish, as a group, produce a wide variety of egg and larval forms in the plankton. Most flatfish species produce pelagic eggs sizes in range from 0.5–0.8 mm for the Pacific sand dab (Citharichthys sordidus) to 4.0–4.5 mm for the Greenland halibut (Reinhardtius hippoglossoides). However, five species in the Pacific Ocean (Marbled flounder Pseudopleuronectes yokohamae, Rock sole Lepidopsetta bilineata, Northern Rock sole Lepidopsetta polyxystra, Dusky sole Lepidopsetta mochigarei and kurogarei Pseudopleuronectes obscurus) and one in the Atlantic (Winter flounder Pseudopleuronectes americanus) have demersal eggs. These species spawn in late winter and spring in shallow coastal waters <20 m depth. Demersal eggs in these waters may be an adaptation to prevent their offshore dispersal by surface currents.
Spawning season varies among flatfish families in relation to latitude. In Pleuronectidae and Paralichthyidae, reproduction is restricted to summer in high latitude waters, while it shifts to spring and winter in temperate waters. Soleidae and Cynoglossidae are distributed at lower latitudes and spawn mainly during summer. Most species are having one single spawning period during the year, some flatfish species spawn bimodal. In high latitude areas, pelagic productivity is high during summer and flatfishes spawn well in advance so that their eggs hatch in the most productive period. In temperate waters, flatfishes mainly utilize the in spring pick and a smaller secondary peak in autumn, when only few species spawn. In tropical waters, productivity is low throughout the year. Spawning may occur at any time, but may be locally linked to the patterns of rainfall or wind. At high latitudes, spawning generally lasts between 2 and 4 months while at low latitudes spawning periods may extend over up to 10 months. Spawning of individual fish takes less time. In North Sea plaice, females were in spawning condition for 3–6 weeks and the length of this stage increased with age. Males are in spawning condition for at least 11 weeks and arrive at the spawning grounds well before the spawning season starts. Young males tended to finish spawning earlier than older males. Most flatfish species are batch spawners, which mean that they release several successive batches of eggs.
Flatfishes generally spawn in water deeper than their juvenile nurseries, and most species have a juvenile stage with fairly specific habitat (such as sediment grain size and temperature preferences) and prey requirements. They tend to move to shallow water to spawn, and nursery grounds for juveniles are shallower than the spawning grounds. The specific location of spawning, as well as depth and directed swimming, play an important role in retention of fish larvae over offshore banks.
The size of larval flatfishes at-hatching can vary from about 2mm for Pacific sand dab to 10–16 mm for the Greenland halibut. Size-at-transformation varies from about 8 mm for Starry flounder (Platichthys stellatus) to 49–72 mm for the Rex sole (Glyptocephalus zachirus). Deep-water dwelling species spawn earlier in the year, generally in winter, spawn larger eggs and have a longer pelagic life, larger larvae and larger size at metamorphosis than shallower dwelling species. The offshore spawning species tend to spend a longer time in the plankton, and metamorphose at a larger size. Flatfish larvae are weak swimmers in the plankton. Larvae with a metamorphic size >25 mm may spend more than 3 months in the plankton. For example, Dover sole (Microstomus pacificus) and Rex sole larvae may spend a year or longer in the plankton. Larvae from warm water and shallower near-shore spawners are smaller and undergo metamorphosis at a smaller size as well. Species with a metamorphic length <10 mm have a pelagic duration <1 month.
The reproductive behavior of Common sole starts when the male approaches a female and works his way under her body. The pair then swims off the bottom with their heads and anterior portion of the body closely pressed closely together and the genital pores adjacent. Spawning always took place at night. The reproductive behavior of the finless sole, Pardachirus marmoratus, consisted of a male and a female resting close together or swimming in pairs with the larger female leading. The male then came to rest on the back of the female with their genital openings in close contact. The reproductive behavior of the winter flounder starts when one or more males follow a female and eventually make contact with her. The female may then avoid the males or a pair may swim in rapid tight circles with the female’s body in a vertical position. Several males were involved with a single female. Very occasionally the female would spawn again a short distance from the first event. All spawning always took place just before sunset or at night.
The reproductive behavior of the Largescale flounder, Engyprosopon grandisquama, Kobe flounder Crossorhombus kobensis, Eyed flounder, Bothus ocellatus, plate fish Bothus lunatus and Bothus ellipticus and in Wide-eyed flounder, Bothus podas are similar. Males defended territories against other males and all spawned during the afternoon or late evening near sunset. Females occupied home ranges within or overlapping the territories of the males. In the Largescale flounder, Engyprosopon grandisquama, males defended territories against other males and agonistic behavior consisted of ‘rearing up’ and ‘parallel swimming’. In this species most males spawned with one or two smaller females within their territories and generally pair formation was assorted by body size. Courtship and spawning consisted of approaches by the male, contact, following and a spawning rise. In Kobe flounder, females indicate readiness to spawn by rapidly raising and lowering their heads. This behavior attracts males who contact the female and then circle around flagging with the pectoral fin. The pair then rises to spawn with the male on top. The only difference in spawning behavior is that the male is positioned below the female during the spawning rise. After the last spawning of the day the males of eyed flounder move to ‘retirement sites’ in shallower water whereas the females ‘retire’ to deeper water. They re-occupy their former territories the following morning.
Importance
Most of these fish have sweet, delicate white flesh that chefs and consumers everywhere enjoy: low fat, fine-textured meat and mild flavor. The flounder is very low in fat, and has a very fine texture and delicate flavor. Flounder is available whole, but more usually as fillets. It can be prepared in any way that respects its fine texture: sautéed, baked, broiled, poached or steamed.
The meat from a flatfish typically varies in color: fillets from the bottom (white) side of the fish will be thinner and whiter, while fillets from the top (dark) side will be thicker and grayer. Even though many of them are called soles, all the flatfish fished commercially in the U.S. are really flounders.
Flatfish include flounder, sole, turbot, halibut, sanddabs, plaice, and tonguefish. This names do not indicate that a fish belongs to a specific family. To show the extent of the confusion:
Witch Flounder (also called Torbay sole or Grey Sole mainly as culinary term), is a right-eyed flatfish belong to family Pleuronectinae has nothing to do with Witch, Arnoglossus scapha, a lefteye flounder of the family Bothidae.
Winter Flounder, Pseudopleuronectes americanus, (also called Blackback or Lemon Sole), has nothing to do with The lemon sole, Microstomus kitt, however they both are right-eyed flatfishes belong to the same family Pleuronectidae.
American Plaice, Hippoglossoides platessoides (also called Dab or Sand Dab), is a right-eyed flounder family Pleuronectidae, has nothing to do with Sanddab, genus Citharichthys, a lefteye flatfish of the large-tooth flounder family Paralichthyidae.
Summer Flounder, Paralichthys dentatus, (also called Fluke), left-eyed flounder family Paralichthyidae. It is a closely related species, California halibut or California flounder, Paralichthys californicus, may also be called fluke on occasion.
Pacific Dover Sole, a flounder not the same as true English Dover Sole from the North Atlantic, is the most common flounder sold on the West Coast.
Yellowfin sole is a small flounder.
Arrowtooth flounder, which is found from California to Alaska, has a soft flesh and is often marketed as turbot, although it is not European turbot, the most expensive flatfish in the world.
Greenland turbot, which is caught in both the North Atlantic and North Pacific oceans, is not really a turbot either, but instead is a member of the halibut family. Outside of North America, it is called Greenland halibut or black halibut. To avoid marketing confusion with Pacific halibut, the halibut industry successfully lobbied to have the name of this flatfish changed to turbot.
The Peacock flounder, Bothus mancus, also known as the Flowery flounder, is a species of lefteye flounders family Bothidae. Eyed side with dark margined light colored spots and numerous scattered small dark spots. Pseudorhombus argus also known as Peacock flounder, is a species of Large-tooth flounders family Paralichthyidae. It has brownish body with 2 double or tripe ocelli above and below lateral line and 1 on lateral line. Many dark spots and rings scattered on body and median fins.
Flatfishes are divided into two groups: the soles, families Soleidae, Cynoglossidae, and Achiridae; and the flounders (including the flounders, turbot, plaice, and halibut), families Achiropsettidae, Bothidae,
Citharidae, Paralichthyidae, Pleuronectidae,
Psettoididae, Samaridae, Scophthalmidae
The Soles
The American soles, of which there are several Atlantic and one Pacific species, have small, close-set eyes and small, twisted mouths with few or no teeth. They prefer warm, shallow water with a sandy or muddy bottom and are generally too small and bony for food. The hogchoker, or broad sole, and the tonguefish, family Cynoglossidae, are most common. The European species The common sole or Dover sole, Solea solea, a 2-ft (61-cm) flatfish found from the Mediterranean to the North Sea, is a the most common valuable food fish.
Family Achiridae (American soles) is fairly small, but mixed family (9 genera with 31 species) of mostly small, dextral flatfishes, up to 14 in (35 cm), found exclusively in temperate and tropical freshwater, estuarine and coastal saltwater of the Americas.
They are small fishes with highly compressed, oval to round disc-like bodies; the eyes close together; snout rounded; mouth small, oblique, a little under snout; lips fleshy, often fringed; eyes small to minute; preoperculum edge covered with skin but visible as a superficial groove; the origin of the dorsal fin well before the eye, the front rays in a skin envelope and hard to see; pectoral present or absent, better developed on eye side, rudimentary or absent on blind side; tail fin not connected to the dorsal and anal fins; both pelvics present, right pelvic may be joined to the anal fin; usually rough scales; lateral line straight, often hard to see, more visible on eye side, usually with perpendicular branches running across body.
Distinguish characteristics:
Eyes are on the right side, and the eyed-side lower lip has a distinctive conspicuous, variously fringed fleshy rim which distinguishes the species of this family from other sympatrical flatfishes. The dorsal and anal fins are usually separate from the caudal fin. The pectoral fins are small or nonexistent. The posterior nare forming a wide longitudinal slit above posterior end of upper lip, and hidden by lower lip when mouth is closed, is also a diagnostic external feature for this family. A similar feature also appears in Soleidae, but it is never covered by lower lip.
Species are bottom inhabitants of sandy or muddy areas from the Gulf of Maine to northern Argentina in the western Atlantic, and from southern California to northern Peru in the eastern Pacific, including a single species at the Galápagos Islands. The greatest diversity of species is found in tropical and subtropical waters within America, some species occur in freshwaters of South America.
Family Cynoglossidae (Tonguefishes) is a diverse family (3 genera with 145 species) of primarily small to medium-sized, sinistral, specialised marine, estuarine and freshwater (few species) flatfishes found circum globally primarily on muddy bottoms and other substrates in shallow, warm temperate, subtropical and tropical marine and estuarine waters, from tide-pools to deep waters on outer continental shelf and upper continental slope (to about 1500 m).
Distinguish characteristics:
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Eyes on left side of body. Lance- or tongue-shaped body highly compressed and tapering to a point posteriorly. Eyes are small and usually close together. No spiny rays in dorsal, anal, and pelvic fins. Dorsal fin reaching far forward onto head, anterior to posterior margin of upper eye; dorsal and anal fins joined to pointed caudal fin; pectoral fins absent; usually only 1 right pelvic fin present.
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Mouth small, subterminal, asymmetrical; reaching posteriorly to point between verticals at anterior and posterior margins of lower eye or slightly posterior to lower eye; jaws moderately curved on eyed side and notably on blind side; teeth minute and usually only on blind-side jaws. Scales small, ctenoid or cycloid (smooth).
Rostral hook usually present below mouth. Posterior margin of preopercle strongly attached to opercle, without free margin and covered with skin and scales. Lips fringed with labial papillae in Paraplagusia. Lateral line none present in Symphurus; Lateral line 1 to 3 on eyed side and 0 to 2 on blind side in Cynoglossus and Paraplagusia. Species of Symphurus are with only a single proximal dorsal-fin pterygiophore inserted into first interneural space; species of Cynoglossus and Paraplagusia with several pterygiophores inserted into first interneural space. Rostral hook absent in Symphurus. Eyed side usually uniformly brownish or greyish, often variably marked with patches, spots, or cross bands on body, and some species with blotches and spots on fins; most species uniformly whitish or yellowish on blind side, others with small indistinct cloudy patches or darker spots.
They are found primarily in estuarine and relatively shallow, continental marine waters of the tropical eastern Atlantic and Indo-West Pacific, with some also occurring in coastal habitats of Indo-West Pacific islands featuring extensive areas of soft-bottom habitats and/or estuaries. In the Western Pacific they are found from the Sea of Japan to southern Australia, including the Philippines and eastward to New Caledonia. Several species inhabit freshwater rivers of Southeast Asia and northern Australia, and some rivers located on larger western Pacific islands, such as Borneo and New Guinea.
Species of Paraplagusia are restricted to shallow, marine waters of the Indo-West Pacific from South Africa to the Indo-Malay Archipelago, to southern Japan, southwards to northeastern and northwestern Australia, and New Caledonia. Symphurus species occur throughout the world’s temperate, subtropical and tropical oceans. Indo-West Pacific symphurine species occur in tidepools and other shallow-water habitats, but the majority of species inhabit relatively deep waters on the continental shelf and upper slope, with some inhabiting depths to about 1500 m. Atlantic and eastern Pacific species occur in both shallow and deep-water habitats to about 1000 m.
Family Soleidae (Soles) is a diverse family (29 genera with 139 species) of specialised, dextral flatfishes of mostly small to medium size is found worldwide in temperate and tropical waters in a variety of marine and estuarine habitats, as well as a few species in freshwater. Most of species inhabit shallow-water marine and estuarine environments, but a few species are found deeper (to about 1300 m). Those species that reach sufficiently large size and attain large populations are highly desirable food fishes targeted by commercial fisheries.
Distinguish characteristics:
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Eyes on right side of body. Preopercle margin not free, embedded in skin. Body is oval or somewhat elongate and strongly compressed. No spines in fins; origin of dorsal fin extending far forward on head to eye; dorsal and anal fins completely separate from, adherent to, or merged with caudal fin; pectoral fins sometimes absent, when present, right usually longer than left; pelvic fins sometimes asymmetrical, either free or joined to anal fin.
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Mouth small and asymmetrical, terminal or slightly inferior; snout sometimes hook-shaped; teeth small, villiform, better developed on blind-side jaws; lower jaw not protruding. Scales moderately large, cycloid or ctenoid, sometimes modified into skin flaps fringed with sensory filaments. Lateral line single and straight on body sometimes branched on head.
Eyed side is highly variable in coloration according to substratum; from uniformly dull brown to strikingly coloured with scattered black spots or blotches or dark cross bands on eyed side of body and vertical fins; blind side usually uniformly yellowish or white.
Some species have widespread distribution and others only fairly restricted occurrence in particular regions. Aseraggodes (19 species) has widespread distribution, with species occurring from East Africa throughout the Indo-West Pacific, to Hawaii, Easter Island and the Galápagos Archipelago. Species of Brachirus (11 species), Soleichthys (14 species), Pardachirus (6 species) and Zebrias (19 species) also occur throughout the Indo-West Pacific region, with some species of Soleichthys occurring also at oceanic sites in the West Central Pacific. Several soleid genera are endemic in the eastern Atlantic including Buglossidium, Dicologlossa, Monochirus, Pegusa and Vanstralenia. Three of four species of Bathysolea are found in the eastern Atlantic, and six or seven species of Microchirus also inhabit this region.
In the eastern Atlantic, soles occur from off southern Iceland (the solenette, Buglossidium luteum) and in continental waters off Europe from southern Norway (Common sole, Solea solea) to Spain and Portugal, throughout the Mediterranean Sea with a few species occurring in the Black Sea, and from North to South Africa (Dagetichthys, 2 species of Austroglossus), throughout the eastern Atlantic and Indian Ocean to the West Central Pacific region. Soles are widespread throughout the Indo-Pacific, with maximum diversity occurring in the Indo-Malayan Archipelago and off northern Australia and New Guinea (Brachirus, Achiroides, Phyllichthys, Paradicula and Rendahlia, each with small numbers of species). They also occur at oceanic islands throughout the Central Pacific extending eastward as far as Hawaii, Easter Island and the Galápagos Archipelago, where this family is represented only by Herre’s sole, Aseraggodes herrei. Soles are conspicuously absent in the western Atlantic, and are rare in the eastern Pacific.
The Flounders
The flounders are much larger fishes, including the fluke (Paralichthys), the halibut (Hippoglossus), the dab (Limanda), and the plaice (Pleuronectes). The smooth flounder is found on muddy bottoms in cold, shallow northern waters. The southern, or winter, flounder (Pseudopleuronectes americanus) is an important food and game fish, taken in large numbers by trawlers. Like other flounders it migrates in winter to deeper waters to breed. It belongs to the righteye flounder family, Pleuronectidae. Similar is the summer flounder (Paralichthys dentatus), of the lefteye flounder family, Bothidae, called fluke by fishermen, common from Maine to the Carolinas. The starry flounder, more brightly colored than its drab relatives, is a common Pacific species found from mid-California N to Alaska and W to Asia. Flounders feed on worms, crustaceans, and other small bottom invertebrates.
The European plaice is an important food fish, as is the American plaice, or sand dab, of which 3,000 tons are taken annually. The American plaice is common at depths of from 20 to 100 fathoms on muddy or sandy bottoms, where it feeds on sea urchins, sand dollars, and other bottom life and grows to 30 in. (76.2 cm) and 14 lb (6.4 kg).
The halibuts are the largest flatfishes and are of great commercial importance. The Atlantic and the Pacific halibuts, Hippoglossus hippoglossus and H. stenolepis, respectively, are very similar, with large mouths and sharp, strong teeth. They feed voraciously on other fish and are found in colder waters. The maximum weight of a halibut is 600 lb (270 kg), but the usual specimens caught offshore at 100 to 400 fathoms weigh from 20 to 100 lb (9-45 kg); the male is generally much smaller than the female. The California halibut, a smaller species (up to 60 lb/27 kg), is found S of San Francisco.
The commercially valuable tribe of European flatfishes called turbots is represented in American waters by a single species, Psetta maxima, commonly called the window pane, found on the Atlantic coast from Maine to the Carolinas. It is much smaller than its European cousins, rarely weighing over 2 lb (.9 kg), whereas the European turbots may reach 30 lb (13.5 kg).
Family Achiropsettidae (Southern flounders) is small family (4 genera with 6 species) of small to medium-size benthic marine flatfishes found in Antarctic and sub-Antarctic waters.
The bodies of southern flounders are greatly compressed. The family varies considerably in size, from the 6.3 cm of Achiropsetta slavae to the 60 cm length of the armless flounder Neoachiropsetta milfordi.
Distinguish characteristics:
Eyes on the left side of the head. Dorsal and anal fins separate from caudal fin and the pectoral fins are rudimentary or entirely absent; none of the fins have spines. The lateral line is straight and well-developed on both sides.
These are the southernmost occurring flatfishes, with the Antarctic armless flounder, Mancopsetta maculata, ranging into continental seas south of Antarctica. Species occur primarily in deep continental shelf and continental slope waters in the Southern Ocean. Also they distributed in southern South America and the Falkland Islands, South Africa, New Zealand, and sub- Antarctic and Antarctic shelves.
Family Bothidae (Lefteye flounders) is large, diverse family (20 genera with 158 species) mostly occur worldwide primarily in tropical and subtropical waters, with the majority of species occurring in relatively shallow marine waters of Atlantic, Indian and Pacific Oceans.
Distinguish characteristics:
Eyes nearly always on left side of head, reversals rare; some species with tentacles on the eyes. Body shape variable, deep to elongate, compressed (size to 88 cm). Edge of preopercle is distinct, not covered by skin and scales. Dorsal-fin beginning above or ahead of front edge of upper eye; no fin spines; urinary papilla on eyed side. Caudal fin usually with 17 rays is not attached to dorsal and anal fins; in some species certain fin rays are elongate in the males. Pectoral fin of blind side presents but shorter than on eyed side. Pelvic fins present with 6 or 7 soft rays but longer on eyed side than on the blind side. Pelvic fin of eyed side on midventral line with origin anterior to origin of pelvic fin of blind side; pelvic fin of blind side above midventral line. Pelvic and pectoral fin rays not divided. Pelvic fins lack a spine. Single lateral line of eyed side with high arch over pectoral fin, there is no lateral line below lower eye. Five series of intermuscular bones present. Males of some species show various combinations of sexually dimorphic characters on head such as wider interorbital areas and rostral and/or orbital spines. Eggs are with only a single oil globule.
Color: eyed side usually with spots, blotches, or rings; blind side light colored except in some species in which males have a dark color pattern on the blind side.
Most flatfishes from this family diverse in the tropical Indo-West Pacific, where species occur from the east coast of Africa and Red Sea throughout the Indian Ocean and Indo-Australian Archipelago, Japan, Australia and New Zealand, and across the Central Pacific. In the western Atlantic they found from about as far north as the seas off Long Island, NY, to about Rio de Janeiro, Brazil. In the eastern Atlantic, they range as far north as southern Scotland, the Kattegat and Christiania fjord, extend into the Mediterranean and Black Seas, and range along the West African coast to South Africa. A few species in a smaller number of genera (Parabothus, Chascanopsetta) occur on the outer continental shelf and upper continental slope.
Family Citharidae (Citharids, Large-scale flounders) is a very small family (4 genera with 7 species) of small to medium-sized marine flatfishes found mostly on sandy bottoms whete they feed on bottom-living animals.
Distinguish characteristics:
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Eyes on left side of head in some species, on right side of head in others, reversals rare. Body is elliptical, moderately compressed. Dorsal-fin origin on blind side above or anterior to posterior margin of upper eye; dorsal and anal fins without spines; urinary papilla on eyed side; caudal fin with 21 to 23 rays (13 to 15 branched) is not attached to dorsal and anal fins; a pectoral fin on both sides of body, with 9 to 13 rays on eyed side, 10 to 13 on blind side; both pelvic fins with short bases, I spine, and 5 soft rays.
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Mouth is large, arched; teeth not greatly enlarged; lower jaw prominent; nostrils asymmetrical (that on blind side being near edge of head). Gill rakers are with small spines slim, elongate, and not tooth-like; gill membranes widely separated. Eyes are either dextral or sinistral. Edge of preopercle is distinct, not covered by skin and scales. Scales large, ctenoid on eyed side, cycloid or weakly ctenoid on blind side; lateral line with high arch over pectoral fins, usually developed on both sides of body. Color: eyed side with some spotting on body and fins; blind side whitish.
They occur in temperate and subtropical seas of Europe and West Africa (Citharus); South Africa, throughout the Indian Ocean, the Philippines, Japan and Western Australia (Citharoides); and widespread in the central and northern Indian Ocean eastward to the Philippines and Australia (Brachypleura, Lepidoblepharon) in the West Central Pacific.
Family Paralichthyidae (Large-tooth flounders, Sand flounders) is a non-monophyletic family of mostly sinistral (a few species with both sinistral and dextral individuals) flatfishes is containing 14 genera with 115 species. This group was historically considered to be a subfamily of an expanded family Bothidae. Most species inhabit shallow muddy and sandy bottoms of the continental shelf in Atlantic, Indian and Pacific Oceans. Some species occur in brackish waters near river mouths. Sand flounders are bottom-dwelling predators, usually burrowing partially or almost entirely in sand or soft mud. Most appear to feed on or near the bottom, but some of the larger species will rise off the bottom to capture prey. Most occur in shallow water, although some species also occur at slope depths (greater than 200 m).
Distinguish characteristics:
Eyes on the left side separated by a bony ridge; posterior edge of the preoperculum free and visible, not hidden by skin or scales. Two nostrils on each side of head, the anterior nostril with a flap posteriorly. Body is ovate (size to 40 cm) with large head, 3 to 4.4 times in standard length. Mouth is rather large, asymmetrical, lower jaw moderately prominent; teeth uniserial, canine-like in both jaws; no teeth on vomer. Gill rakers are palmate, of moderate length or short, with posterior serrations. Dorsal-fin is long, originating above, anterior to posterior edge of upper eye; no fin spines in pectoral and pelvic fins. Dorsal and anal fins not attached to caudal fin. Caudal fin double truncate with 17 or 18 rays, 10 to 13 rays branched (usually 11 or 13, rarely 10 or 12). Both pectoral fins present, not elongate, middle 6 to 9 rays branched on eyed side, but all rays unbranched on blind side. Both pelvic fins present on both sides of body, with 5 or 6 branched rays (6 rays in nearly all species). Pelvic fin bases are short, subequal and nearly symmetrical, posterior with 3 or 4 branched rays.
Lateral line equally developed on both sides of the body, either straight (Cyclopsetta group) or with a distinct curve above pectoral fins (Paralichthys group) and the latter with a branch under lower eye, running upward to anterior part of dorsal fin. Lateral line present (Paralichthys group) or absent (Cyclopsetta group) below lower eye. Urinary papilla is on ocular side (Paralichthys group) or blind side (Cyclopsetta group), not attached to first anal-fin ray. Scales cycloid or ctenoid on both sides; 4 plates of caudal skeleton with deep clefts along distal margins. Paralichthids often are sexually dimorphic in the length of their dorsal and pectoral fins. Some species of the Cyclopsetta group (some species of Syacium, Citharichthys, and possibly Etropus) show sexual dimorphism in interorbital width, length of the pectoral fin on the ocular side, length of the anterior dorsal-fin rays, and coloration. Eggs with a single oil globule in the yolk.
Color: ocular side uniformly brownish, pale greenish or greyish, often with dark spots or rings, sometimes with double ocelli; blind side usually pale; although ambicoloration (eyed-side coloration replicated on blind side) may occasionally occur. They are capable of a rapid change in coloration which allows them to match their background almost perfectly.
They are distributed worldwide in tropical, subtropical and temperate seas. In the western Atlantic, 9 genera occur from the Gulf of Maine to southern Argentina. Only a single species each of Syacium and Citharichthys represent this family in the eastern Atlantic off West Africa. Only 2 of 11 paralichthyid genera, Pseudorhombus (23 species) and Tarphops (2 species), are found entirely in the Indo-West Pacific, with species ranging from East Africa and the Red Sea throughout the Indian Ocean and Indo-Australian Archipelago to the western Pacific, including Korea and Japan. A third genus, Paralichthys, is represented in the western Pacific by a single species (Japanese flounder, Paralichthys olivaceus).
The greatest diversity of genera and species of paralichthyids occurs in seas of the New World, especially the Caribbean Sea and tropical eastern Pacific. 14 out of 15 species of Paralichthys have totally New World distributions (8 western Atlantic, 6 eastern Pacific). 8 species of Hippoglossina also are restricted to the western Atlantic and eastern Pacific oceans.
Family Pleuronectidae, Righteye flounders are found at depths of about 60 to 500 m on soft bottoms composed of mixtures of mud, sand, silt, and crushed shells. Some shallow-water species occur as shallow as 6 m in or on sands around coral reefs. One species (Samaris cristatus) occurs in fairly shallow water.
Distinguish characteristics:
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Eyes on right side of head; reversals rare. Edge of preopercle is distinct, not covered by skin and scales. Body oval-shaped or elongate, strongly compressed (size to about 22 cm). Dorsal-fin origin anterior to posterior margin of upper eye; no fin spines; urinary papilla on eyed side; caudal fin not attached to dorsal and anal fins; pectoral fin on blind side smaller than fin on eyed side or missing; pelvic-fin bases short or somewhat elongate, fin on eyed side slightly anterior to that of blind side and closer to or on midventral line.
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Mouth and teeth are small. Gill rakers elongate, not tooth-like. Scales are small; lateral line weakly developed or missing on blind side of body. Anterior dorsal-fin rays and rays of pelvic fin on eyed side greatly elongate in Samaris. Color: body on eyed side often with spots or blotches on body and fins; blind side whitish.
Family Psettodidae, Spiny Turbots, the most primitive family of the flatfishes. There is a single genus with 3 species, 2 of which are restricted to tropical West Africa and 1 Indian halibut, Psettodes erumei, is distributed in the Indo-West Pacific from South Africa to Australia and Japan.
Distinguish characteristics:
Evidence of the primitive nature of this family is the presence of spines in the anterior part of the dorsal fin, the origin of this fin well behind the eyes, and the pelvic fins with a spine. Also they sometimes swim in an upright position. Other characteristics are a large mouth with large canine teeth in the jaws, some of which have barbed tips; minute teeth on vomer, platines, and tongue; margin of the preopercle not covered by skin; cycloid scales; and lateral line developed on both sides of the body.
Family Samaridae, Crested flounders, is a family of small-sized, dextral flatfishes containing 21 species in 3 genera (Plagiopsetta, Samaris, and Samariscus) distributed in the Indo-West Pacific. Samarid flatfishes formerly were included with the family Pleuronectidae. They are marine species habitat in tropical and subtropical, primarily in deep water. Species numbers are highest in the Indo-Malaysian region, drop off with increasing distance and are not found in the extreme eastern Pacific due to the eastern Pacific barrier. They distributed from East Africa and the Red Sea to northeastern and northwestern Australia, China, southeastern Japan, the Philippines, Hawaiian Island (1 rare species occurs at diving depths in Hawaii), and eastward to the Sala-y-Gomez Submarine Ridge in the eastern Pacific.
Plagiopsetta glossa, the tongue flatfish, is found from southern Japan to Australia and New Caledonia, whereas species of Samaris occur in continental seas off South Africa and along eastern Africa, off Madagascar, Reunion Island, in the Red Sea, and from the northern Indian Ocean, China, the Philippines, Indo-Malay Archipelago, and across northern Australia to New Caledonia.
Distinguish characteristics:
These flatfishes have both eyes on the right side of the head. Origin of dorsal fin is in front of eyes; lateral line well developed or rudimentary; pelvic fins symmetrical; 16 caudal fin rays; postcleithra absent (this is also true for the Achiridae, Soleidae, and Cynoglossidae).
Family Scophthalmidae, Turbots, is a small family of sinistral flatfishes, benthic on the continental shelf, occurring in the northern Atlantic, the Baltic, the Mediterranean and the Black Sea. It contains 10 species in 4 genera, 2 of them, the Brill (Scophthalmus rhombus) and the Turbot (Scophthalmus maximus), are valuable commercially and have been caught and stored salted since ancient times, in the middle ages of Europe. Moreover, the turbot is the first flatfish species that has been reared successfully in aquaculture farms; larvae, juveniles and adults, as well as fillets of this species are exported all around the world. Feed on benthic invertebrates and small fish. Some species reach a sufficient size and are abundant enough to be important for fisheries.
Distinguish characteristics:
Eyes are sinistral and located on left side. Preopercular margin is free. Mouth is large with prominent lower jaw. Lateral expansions, slightly asymmetric, on both pelvic bones. Bases of both pelvic fins are elongate; an anterior extension of the two pelvic fins to the isthmus. Anus is on blind side. Dorsal and anal fin rays shortened posteriorly; first neural spine with an anterior process, often bent, forming a bridge contact with the dorsal margin of the right cranium. Asymmetrical transverse apophyses on the caudal vertebrae. Gill membrane widely separated. Egg with a single oil globule in the yolk.
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