Stromateoidei (Butterfishes and Relatives)
(Butterfishes and relatives)
Number of families 6
Evolution and systematics
The fossil record of the Stromateoidei is not very extensive, consisting mostly of isolated otoliths, the paired earstones present in the membranous labyrinth of the inner ear of many fishes that can aid in detecting motion. Otoliths are difficult to identify because they usually lack the diagnostic features of families of fishes. Irrespective of this, the earliest otoliths attributed to a stromateoid date from the early Tertiary period (about 50 million years ago), of France, Belgium, and England. Fossils known from more than otoliths, such as skeletons, are rare, and these are also fragmentary, such as Psenicubiceps alatus from Russia, currently assigned to the stromateoid family Nomeidae. The earliest stromateoid fossils are believed to be from Denmark, from deposits as old as 60 million years, but these cannot presently be assigned with confidence to the Stromateoidei.
The Stromateoidei is a suborder of the large bony fish order Perciformes. The composition of this suborder has changed only slightly in the past 35 years; it was mostly assembled in a landmark study in 1966 by Humphry Greenwood, Donn E. Rosen, Stanley H. Weitzman, and George S. Myers, in which all families were grouped together except the Amarsipidae, which was added in 1969. The Stromateoidei currently includes 6 families, 15 genera, and some 65 species. The families are: Amarsipidae (with a single genus and species, Amarsipus carlsbergi), Nomeidae (driftfishes; 3 genera and 15 species), Centrolophidae (medusafishes; 7 genera and 27 species), Tetragonuridae (squaretails; 1 genus, Tetragonurus, and 3 species), Stromateidae (butterfishes; 3 genera and 13 species), and Ariommatidae (1 genus, Ariomma, and 6 species).
Within the Perciformes, stromateoids are more closely related to certain generalized families that share a specific arrangement of the ramus lateralis accessorius (a facial nerve complex), including the Kyphosidae, Girellidae, Scorpididae, Arripididae, Kuhliidae, Microcanthidae, Oplegnathidae, and Terapontidae. Of these families, the stromateoids are more closely related to the Kyphosidae (chubs), sharing with them details of their tooth pattern and larval pigmentation. Evolutionary relationships within the Stromateoidei indicate that the Amarsipidae are the most basal group, that the Centrolophidae may not have unique features, and that the butterfishes (Stromateidae) are the most derived stromateoids.
Stromateoids are moderate-sized fishes up to 47.2 in (1.2m) in length, generally with round and somewhat large eyes (with associated adipose tissue in ariommas), small mouths, forked caudal fins (with 15 branched rays), and elongated dorsal fins that may be continuous or subdivided. The body is slender to deep, and is either compressed laterally or rounded in cross-section. The dorsal fins have spines (weak in some species); an anal fin with one to three spines; the dorsal and anal fins generally terminate at the same level; pelvic fins are absent in adults of some species (e.g., butterfishes, although the pelvic bones are present); pelvic fins are small in others, and very large in the man-of-war fish (Nomeus gronovii). The jaw teeth are small, usually arranged in a single series; the nostrils are double; a lateral line is present. The gill rakers range from 10–20 on the first gill arch. Scales are usually cycloid. Coloration may vary from silvery to dark brown in adults, but is usually mottled in juveniles. Some species have more elaborate color patterns, with blotches and bands.
Stromateoids, with the exception of the Amarsipidae, are unique in having a specialized pharyngeal organ (the pharyngeal sac) just anterior to the esophagus and following the last gill arch, which is specialized for further breaking down food items. The pharyngeal sacs are coated internally by small projections (papillae) that contain minute "teeth"; the structure and arrangement of the papillae vary significantly among species. All stromateoids share a specific configuration of the internal caudal fin skeleton.
Stromateoids are found in all major oceans (except the Arctic, Baltic, Okhotsk, and Black Seas, and the Antarctic Ocean) from the high seas well offshore, to the continental shelf regions, and in large bays. They are more common in temperate and tropical waters, but a few species also occur in colder areas. Many offshore pelagic species are very widely distributed.
All stromateoid species are marine. Some eight genera are oceanic, six genera are mostly coastal, and two are both coastal and oceanic. As a general rule, young individuals are usually epipelagic, sometimes living in association with jellyfishes, but adults occur mostly in deeper waters, either demersally (in-shore or offshore down to about 1,640 ft/500 m); more in some species, but usually in shallower waters) or mesopelagically.
The behavior of individual stromateoids, other than in relation to their association with jellyfishes, is virtually unknown. Many species form schools of moderate size, as individuals are frequently captured together. The association between stromateoids (usually juvenile) and jellyfishes requires further study, but it appears to form very early in the fish's development. Stromateoids are more resistant to jellyfish toxins than other fishes. They may also associate with salps (semitransparent barrel-shaped marine invertebrate animals), where juveniles of squaretails may seek refuge. They usually hover underneath the bell of the jellyfish, but may swim in and out of its tentacles to snatch prey items (mostly zooplankton and other invertebrates). They may also feed occasionally on the tentacles and gonads of the jellyfish, and are also subjected to predation by them. Juveniles in association with jellyfishes are usually more colorful or display more complex color patterns than adults of the same species, which are usually demersal or pelagic. Individuals of some species (e.g., the barrelfish, Hyperoglyphe perciformis) may congregate under floating wreckage, oceanic flotsam, planks, buoys, or other sheltered mobile habitats. Others may gather around vessels.
Feeding ecology and diet
Food items consist mostly of invertebrates (numerous crustaceans, such as barnacles, crabs, shrimps, and euphausiids (small shrimp-like crustaceans), in addition to squids, various other mollusks, and zooplankton), but many species have a predilection for jellyfishes. Small fishes may be taken occasionally, as well as urochordates. Stromateoids are preyed upon by larger fishes, including sharks, and also by their jellyfish hosts.
As with many pelagic fishes, stromateoids are broadcast spawners, releasing large quantities of eggs into the pelagic realm upon spawning. Spawning may occur on a yearly basis during the summer months in some species, but spawning periods are unrecorded for many stromateoids. The eggs are small, ranging from 0.03–0.07 in (about 0.07–0.18 cm) in diameter, when known; they are spherical, separate, and pelagic; and usually contain a single oil droplet. Hatching usually occurs under 0.2 in (0.5 cm) in length, and flexion takes place shortly thereafter. Depending on the species, juveniles begin to resemble adults at about twice their flexion length. The eggs and larvae of about one-half of all stromateoid species have yet to be described.
No species are listed by the IUCN.
Significance to humans
Some stromateoid species are of commercial importance locally, especially in Japan and Southeast Asia. Among the most important species are the silver pomfret (Pampus argenteus), with a yearly catch ranging from 11,000 to 18,000 tons (11,177–18,289 t) between 1990 and 1995; the Indian ariomma (Ariomma indicum), with a yearly catch reported at 9,000 tons/9,144 t off Africa; and the American butterfish (Peprilus triacanthus). Most other species are of little or no importance commercially. All species are harmless.
List of SpeciesBlack ruff
Perca nigra Gmelin, 1788, eastern Atlantic.
other common names
English: Blackfish; French: Centrolophe noir; German: Schwarzfisch; Spanish: Romerillo.
Length 43.3 in (110 cm). Elongate, with a rather small head and large eyes; continuous dorsal fin extends most of the length of the body (with 4–5 weak spines and 32–38 rays); anal fin with 3 spines and 20–27 rays; pelvic fins small, under pectorals; pectorals with 19–23 rays; caudal fin weakly forked; mouth rather wide, extending posteriorly beneath eyes; coloration dark bluish gray, but sometimes darker.
Temperate oceanic waters. Young specimens occur near surface; larger individuals are mesopelagic. Specimens have been captured as deep as 1,968 ft (600 m) off Australia and New Zealand.
Little is known concerning its behavior. Small specimens have been found in association with jellyfishes, but adults may form schools.
feeding ecology and diet
Feeds on jellyfishes, squids, and different kinds of crustaceans. Preyed on by hake and possibly other larger fishes.
Eggs and larvae are pelagic; eggs are spherical, small (0.05 in/0.12 cm in diameter) and contain a single oil globule. Hatching occurs at about 0.16 in (0.4 cm) standard length, flexion at 0.2 in (0.6 cm), adult body form attained at 0.7 in (1.7 cm). Growth reported to be relatively fast. Probably a broadcast spawner.
significance to humans
Not significantly consumed and therefore of minor importance.
Gobius gronovii Gmelin, 1788, eastern Atlantic.
other common names
English: Bluebottle fish, shepherd fish; Spanish: Pastorcillo, Pez azul.
Standard length 13.7 in (35 cm). Head somewhat tall, body tallest at level of pelvic fins, tapering posteriorly; dorsal fin continuous, originating at midbody length, with 9–12 spines and 25–27 rays (IX–XII, 24–28); pectoral fins elongate, with 21–23 rays; caudal fin forked, with some 15 rays; anal fin with two spines and 24–29 rays (I–II, 24–26); pelvic fins very long and prominent, reaching posteriorly to level of pectoral fin extremities, with one spine and five rays (I, 5); eyes large; no teeth on tongue. Juveniles have vertical, dark blue and broad bands, with blue blotches on head and fins; adults have irregular blue blotches on body, head, and fins; background color silvery, pelvic and dorsal fins black. Larger adults more uniformly dark in color.
Tropical and warm temperate waters of Atlantic, Pacific, and Indian Oceans.
Pelagic offshore, usually warm waters, commonly found in association with the siphonophore Portuguese man-of-war (Physalia), but larger adults may live independently in deeper waters. Juveniles may be found pelagically in waters 98 ft (30m) deep.
Usually found in large numbers living underneath the bell of the Portuguese man-of-war, swimming in and out among its tentacles. The mottled color pattern mimics the tentacles of Physalia. It lives commensally by being resistant to the venom of the siphonophore.
feeding ecology and diet
Feeds on the tentacles and gonads of the Portuguese man-ofwar, zooplankton, and other soft-bodied jellyfishes. Sometimes eaten by its host.
Eggs and preflexion larvae are unknown; postflexion larvae as small as 0.27 in (0.7 cm) have been recorded, and adult form is mostly attained by 0.9 in (2.5 cm). Other aspects of its reproduction are unknown, but as with other stromateoids, eggs and larvae are pelagic and they are probably broadcast spawners. Small individuals of 0.39 in (1 cm) have been found in association with the Portuguese man-of-war, indicating that this association forms early in life.
significance to humans
Of minor commercial importance, due to infrequent fishing.
other common names
English: American butterfish; French: Stromaté fossette; Spanish: Palometa pintada.
Length about 11.8 in (30 cm). Body thin and deep, with short head and blunt snout. Single dorsal fin is taller shortly posterior to its origin, with 2–4 spines and 40–48 soft rays (II–IV, 40–48); pectoral fins moderately elongate with 1–22 fin rays; 22–25 gill rakers; lateral-line scales 96–105; anal fin almost as long as dorsal fin, with 3 spines and 37–44 rays; caudal fin deeply forked with slightly greater lower lobe. Pelvic fins absent. Color grayish blue above and silvery on sides, with many irregular dark spots laterally.
Western Atlantic Ocean, from off South Carolina, United States, to Nova Scotia (sometimes as a stray off the coast of Newfoundland); also further south to the coast of Florida, United States, in deeper water, as well as in the Gulf of Mexico.
Continental shelf; found pelagically or demersally in waters as deep as 600 ft (183 m), usually over sandy bottoms. May venture into shallow bays and estuaries.
Little is known concerning behavior other than reproduction. During the first year may live in association with jellyfishes or freely, but forms schools as adults. Migratory patterns are common in consequence of water temperature. Appear seasonally off northeastern coast of the United States, but are generally unpredictable as to when.
feeding ecology and diet
Feeds abundantly on soft-bodied invertebrates, preferring urochordates and mollusks. Also feeds on cnidarians, ctenophores,
chaetognaths, polychaetes, and crustaceans (including amphipods, copepods, mysids, and euphausiids). Juveniles in Narraganset Bay, Rhode Island, United States, feed heavily on ctenophore Mnemiopsis leidyi, not by ingesting it whole but by taking small bites. Feeding occurs both day and night. Preyed on by some 30 species of fishes and squids, and are part of the diet of many commercially important fishes, such as haddocks, bluefishes, swordfishes, summer flounders, and hammerhead sharks.
Sexually mature between first and second years, starting about 7.1 in (18 cm) standard length (i.e., exclusive of the caudal fin). Broadcast spawners, lack specialized courtship behavior. Spawning takes place once a year during summer months. Eggs are buoyant, spherical, and transparent, measure some 0.03 in (0.08 cm) in diameter; include a single oil droplet. Larvae begin to resemble adults about 0.6 in (1.5 cm), when fin rays of dorsal, anal, and caudal fins are fully formed.
significance to humans
Important commercial fishes, heavily consumed since the 1800s, and commonly caught by otter trawls, gill nets, and other means. In the early 2000s, yearly catches averaged under 4,921 tons (5,000 t), but in 1973 close to 19,684 tons (20,000 t) were landed. The flesh is considered to be very delicious and "melt-in-your-mouth," which is reflected in the common name.
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Marcelo Carvalho, PhD