Gasterosteiformes

(Sticklebacks, seahorses, and relatives)

Class Actinopterygii

Order Gasterosteiformes

Number of families 11

Evolution and systematics

The evolutionary affinities and composition of the Gasterosteiformes have been the subject of much debate; presently they are considered to be closely related to the teleost fish orders Synbranchiformes (swamp eels), Elassomatiformes (pygmy sunfish, Elassoma), Mugiliformes (mullets), and the collective Atherinomorpha (silversides, needlefishes, killifishes, and allies) and are placed with them in the larger group Smegmamorpha. Smegmamorphs are characterized by a unique configuration of the first vertebra and its associated intermuscular bone. Within this group, gasterosteiforms may be more closely related to the Synbranchiformes, but relationships within smegmamorphs are still the subject of controversy. The smegmamorphs, in turn, are closely related to the largest of all teleost groups, the Percomorpha. This evolutionary arrangement is the most recent and best-supported hypothesis based on morphological evidence, but alternative schemes of relationship have been proposed (including molecular studies), and a true consensus has not yet emerged.

The Gasterosteiformes, as described in this chapter, comprises two suborders, the Gasterosteoidei and the Syngnathoidei. Other authors sometimes have recognized these as separate orders, but evidence exists that they are each other's closest relative and therefore warrant being classified together. Gasterosteiformes share various specializations, such as pelvic bones without anterior processes, absence of Baudelot's ligament (a stout ligament connecting the shoulder girdle to either the posterior cranial base or an anterior vertebra—also absent in synbranchiforms), certain features of their branchial and caudal skeletons, and a particular configuration of their scales, which are represented by enlarged scutes, or plates. (Scales are absent in Hypoptychus, Aulostomus has small ctenoid scales, and Fistularia has embedded spines).

The extent to which these features (and others) are truly indicative of a common ancestry for Gasterosteiformes is not completely understood.

The Gasterosteoidei includes the following families: Hypoptychidae (for the sand eel, Hypoptychus dybowskii), Aulorhynchidae (tubesnouts, two monotypic genera), Indostomidae (Indostomus, with three species), and Gasterosteidae (some five genera and, conservatively, seven spp.). The Syngnathoidei comprises the families Syngnathidae (seahorses and pipefishes, with about 52 genera and 220 spp.), Aulostomidae (trumpetfishes, Aulostomus, with some three spp.), Fistulariidae (cornetfishes, Fistularia, with four spp.), Macroramphosidae (snipefishes, three genera with 12 spp.), Centriscidae (shrimpfishes, two genera with four spp.), Solenostomidae (ghost pipefishes, Solenostomus, with some four spp.), and Pegasidae (seamoths, two genera with five spp.). Altogether, the order Gasterosteiformes is represented by 11 families, 70 genera, and at least 265 species, but undescribed species have been discovered (including some 20 species of pipefishes and seahorses), and numerous nominal species presently in synonymy, in fact, may be valid (such as for sticklebacks). Much work remains to be done concerning their taxonomy, and the phylogenetic position of Indostomus is still debated.

The fossil record of the Gasterosteiformes is extensive and dates back at least some 75 million years to the Calcare di Mellissano deposits near Nardò, in southeastern Italy (Apulia). This early fossil, Gasterorhamphosus zuppichinii, is known from skeletal remains and is similar to modern snipefishes. Additional gasterosteiform fossils, known from more or less complete skeletons, have been described from the extensive Monte Bolca beds of northeastern Italy (dating back some 52 million years). These include representatives of the Syngnathidae (at least five genera), Solenostomidae (some three

genera), Centriscidae (three genera), Aulostomidae (four genera), and Fistulariidae (some three genera and four spp.). The actual number of species from Monte Bolca is difficult to estimate with precision, but this formation represents the greatest extinct diversity of the order. The gasterosteiform species present in both the Nardò and Monte Bolca deposits were inhabitants of the former Tethys Ocean, which separated the extinct continents Laurasia and Gondwana during much of the Cretaceous and Tertiary periods. Other fossils, mostly represented by fragmentary material and allied to the Aulostomidae and Fistulariidae, are known from Turkmenia, in deposits almost contemporaneous with Monte Bolca. Fossil sticklebacks have been found in the Tertiary of California (Monterey Formation) and Siberia. Tertiary pipefishes have been described from the Modelo and Puente Formations of southern California as well as from the Caucasus and Carpathian Mountains of eastern Europe.

Physical characteristics

The morphological characteristics of various gasterosteiform families are highly modified and specialized; some of the members of this order are among the most morphologically interesting of all fishes. Some forms are more pelagic and streamlined (e.g., aulorhynchids), whereas others

are benthic and highly cryptic (e.g., pegasids). Many forms are elaborately camouflaged and blend in perfectly with their surroundings (some of the most notable examples are Syngnathus typhle, Solenostomus cyanopterus, and Histiogamphelus cristatus); some syngnathid species have been discovered only after their particular substrate was collected and examined. Additionally, some species carry algal growths and complex dermal projections that further aid in their concealment (the most striking example may be the leafy seadragon Phycodurus eques), and many species have the ability to change color at will (e.g., Aulostomus chinensis). Most species have the head and body on the same plane, as in "typical" fishes, but seahorses have the head at more or less a right angle to the body, a unique condition among fishes.

There is much morphological variation among the families and subfamilies, and many are recognized easily by their unique designs. Gasterosteids (sticklebacks) resemble more "typical fishes," with an unmodified head and clearly demarcated fins, but most gasterosteiforms have elongated snouts, with small upturned mouths, and may lack some fins or even all of them (Bulbonaricus). The snout may be absent (Bulbonaricus); truncated (Histiogamphelus); mildly elongated (Indostomus); or very long and tubular, reaching up to one-third of their total length (e.g., Aulostomus and Fistularia). The mouth usually is very small, located at the end of the snout (except in pegasids, where the mouth is underneath the snout), and most species lack teeth. The eyes typically are round and vary from large to small. Most species have very slender and elongated bodies, but gasterosteoids (except Indostomus) and some syngnathoids (e.g., Macroramphosidae, Centriscidae) are laterally compressed.

The fins typically are highly modified. They have either one or two dorsal fins; the single dorsal fin may be preceded by numerous spines (gasterosteoids, Aulostomus), but in some forms the spines represent the first dorsal fin (Solenostomus, centriscids, and macroramphosids). In most species, however, there is a single dorsal fin with soft rays only. Pelvic fins are absent in Hypoptychus and syngnathids, and the caudal fin is absent in most syngnathids. Many syngnathids have prehensile tails that enable them to cling to soft corals and algae. Most gasterosteiforms are covered in bony plates, scutes, or rings and have numerous elaborate dermal projections on the head, body, and tail. There is also great morphological variation internally (e.g., lack of true stomachs in seahorses and reduction of the number of cephalic bones in many species). Details of the morphological features of the different families are elaborated in the species accounts.

Gasterosteiforms are among the most colorful fishes, displaying a wide spectrum of colors and patterns. There is also much diversity in coloration within certain species, and some individuals may change color while breeding or to blend into different backgrounds. Every conceivable color pattern seems to be present within the order, as some species combine strong colors (e.g., red, orange, yellow, green, white, black, and blue) with spots, blotches, ocelli, mottlings, and stripes of various kinds. Gasterosteiformes also vary considerably in size, from some 0.8 in (2 cm) in length among pygmy seahorses to more than 4.9 ft (1.5 m) for cornetfishes (Fistularia).

Distribution

Worldwide in tropical and temperate marine waters as well as in temperate freshwaters of the Northern Hemisphere. Species are more abundant in the tropical Indo-West Pacific region, where several undescribed pipefish species are known. Some species are widespread (e.g., the red cornetfish, Fistularia petimba), whereas others are very restricted in distribution (e.g., Festucalex cinctus off central New South Wales and southern Queensland, Australia). A few species with wide distributions, such as Hippocampus erectus and Doryrhamphus dactyliophorus, may require subdivision.

Habitat

Most species are coastal residents, present in shallow continental shelf areas in a variety of habitats, such as coral reefs, atolls, offshore reefs, sea grass meadows, kelp forests, tide pools, estuaries, bays, and lagoons and over sandy or muddy bottoms. Many species live cryptically, hiding among rocks and crevices in reefs or blending in with gorgonian corals or sea grasses. Many species have pelagic young, which eventually settle closer to the bottom. Some 20 gasterosteiform species are freshwater (at least one stickleback is exclusively so, along with Indostomus and pipefishes of the genera Microphis, Hippichthys, and Dorichthys) and are present in a variety of habitats, including lakes, coastal rivers, creeks, marshes, and protected coastal inlets. Some 40 species are euryhaline, found in brackish environments. As far as is known, no species occurs in deep-water environments.

Behavior

Gasterosteiforms are diurnal as far as is known. Most species are solitary or live in pairs or small groups or sometimes in larger groups (e.g., aulorhynchids). Many species have pelagic young, but most adults are benthic. A few species, such as macroramphosids and aulorhynchids, form schools, sometimes containing thousands of individuals. Most species remain in association with soft corals, hard corals (Hippocampus barbouri), algae, sea grasses, or other substrates, where they

are well camouflaged; in many cases they grasp the reef with their prehensile tails. Many species appear sluggish owing to their somewhat sedentary lifestyle and lack of ability to move very swiftly. Syngnathids swim by a combination of movements of their pectoral and dorsal fins, and some species swim by moving their tails from side to side. Many syngnathids appear to hover in one location, controlling their position by coordinated movements of their pectoral and dorsal fins. Some pipefishes (e.g., Heraldia) are able to swim in an upside-down position in caves and crevices. Centriscids remain in a vertical position, with their mouths directed toward the bottom, sometimes in association with urchins. Species of pipefishes, Solenostomus, Aulostomus, and macroramphosids also maintain a vertical position at times. Many species can change their coloration according to their background, using this ability to sneak up on prey or to hide from predators. Some species, especially pipefishes (e.g., Doryrhamphus spp.), have been documented to clean other fishes (e.g., moray eels and damselfishes), removing their parasites while in reefs.

Feeding ecology and diet

Most syngnathoids feed on a wide variety of small crustaceans (e.g., copepods and mysids), sometimes almost exclusively, as well as on other small invertebrates and the larvae of other fishes. The larger species, such as cornetfishes and trumpetfishes, also feed on larger fishes. Most gasterosteiform species ingest prey whole by quickly opening their mouths to produce a strong inward current, a suction mechanism called pipette feeding. In this manner, large prey items cannot be ingested, owing to the small terminal mouths, lack of teeth, and tubular snouts of many syngnathoid species. Most prey items are ingested from the substrate or when just hovering above it. Many gasterosteiforms rely on their highly developed camouflage to surprise prey items. This is the case in numerous species of pipefishes that slowly cruise over sandy bottoms with sea grasses, feeding on small crustaceans that fail to perceive them as a result of their cryptic appearance. Many species feed on small mysids and other crustaceans that are more free-swimming as well as fish larvae; they remain in strategic positions along the fringes of reefs, where they are exposed to currents that may contain these prey items. Some species, however, eat primarily in the water column (e.g., macroramphosids and aulorhynchids). Gasterosteiforms are preyed upon by larger carnivorous fishes, such as flatheads (Platycephalidae) and snappers (Lutjanidae). Because they move slowly, gasterosteiforms are ingested easily once they are discovered.

Reproductive biology

A great variety of reproductive strategies occur in this order, including some of the most elaborate known for any group of fishes. In a few families (Centriscidae, Macroramphosidae, Pegasidae, and perhaps Aulorhynchidae), the eggs and larvae are pelagic, and spawning probably is accomplished (at least in some of these families) in a style similar to broadcast spawning, in which eggs and sperm are released directly into the water column. In pegasids, spawning involves a courtship ritual whereby a female and a male swim vent to

vent, releasing eggs and sperm simultaneously. In other families, reproduction is a far more complex process in which the male carries the eggs, sometimes in a special pouch, within which the eggs may be fertilized. In Solenostomus, the females carry the fertilized eggs in pouches made of their greatly extended pelvic fins, repeatedly opening and closing them to fan the eggs. As a preliminary behavior to spawning, many species employ complex courtship rituals, in which males compete for the female by dancing, inflating their pouches, or performing in some other way. A male stickleback lures the female into his nest and fertilizes the eggs there, sometimes attracting several females in succession. Some species are reproductively active throughout the year, whereas others are seasonal. Many species of syngnathids form monogamous pairs.

Reproduction has been studied in detail for many syngnathids. In seahorses, the females insert their eggs into the pouch of the males, using an abdominal projection known as the ovipositor (an everted egg duct); the eggs are fertilized by the sperm located in the pouches. During this process the male and female face each other. Inside the pouch the eggs are enveloped in tissue that supplies oxygen to the eggs (through diffusion from capillaries) as well as hormones by bathing the small portion of the egg that protrudes from the surrounding tissue. The pouch remains sealed. The male carries the eggs to term (incubation may last from 10 days to six weeks, depending on the species and surrounding temperature), during which time he appears very pregnant. The male actively expels the young (by forcefully moving back and forth) over a period of a few hours through an opening at the top of the pouch. Usually, about 100 young are born in this manner, but some species produce up to 400 young, whereas others produce between 10 and 50 (measuring close to 0.4 in, or 1 cm); pairs may have several broods in one year. The young do not receive any further parental care and are on their own immediately after birth. Young may congregate, and their sexes can be distinguished after a few months, when the pouches of the males become apparent (i.e., when they become sexually mature). Young resemble adults shortly after birth. As many as 1,000 young are produced per year by each couple in this manner, although the actual number varies between species, as reproduction may occur continuously.

Many pipefish males carry the eggs in the anterior tail region (just underneath the dorsal fin) without enclosing them in a pouch, fertilizing the eggs when they are deposited. The eggs are clearly visible in these cases. Courtship has been observed in detail in the species Corythoichthys isigakius from Japan. In this species, after a couple has consented to mate, the male and female repeatedly circle each other with their heads raised, exposing their undersides while remaining in an almost vertical position. When the male is ready to incubate the brood and the female is full of eggs, they practice egg transfer for several days until the process is actually enacted. The male's tail is flattened laterally as an indication that he is able to receive the eggs. The female places her small, greenish eggs on his tail, pushing them into place so that they remain attached. The eggs hatch after a few weeks. Hatching may be helped by the male, who shakes vigorously until all the eggs have separated. The young then are ready to begin their short pelagic life.

Conservation status

A relatively large number of gasterosteiform species are listed by the IUCN. Most of the threats that these species face are related to the pervasive seahorse trade, especially in southeastern and eastern Asia, and to widespread habitat degradation. Gasterosteiforms generally are not directly consumed in quantities that would otherwise place them in danger of overexploitation. Overexploitation of seahorses is a result of their use as ingredients for prepackaged medicines, where demand far exceeds supply, and for the curio and aquarium trade. Many species live in coastal or estuarine habitats, which typically are more affected by development and pollution. Furthermore, the vulnerability of seahorses is enhanced by their low fecundity, parental care, and complex social structures. The IUCN presently includes in their compilation of threatened taxa about 51 species of gasterosteiformes. The majority of species are listed either as Data Deficient or Vulnerable (all species of seahorses and many species of pipefishes). The Cape seahorse (Hippocampus capensis) is listed as Endangered (mostly due to commercial development of its restricted habitat), and the stickleback (Pungitius hellenicus) and the river pipefish (Syngnathus watermeyeri) are listed as Critically Endangered. Conservation efforts, mostly geared toward seahorses, are presently being undertaken by Project Seahorse, a praiseworthy initiative that aims to promote the sustainable exploitation of seahorses and their relatives.

Significance to humans

Numerous species of this order are popular fishes sought out by recreational divers. Many are important aquarium fishes and, fortunately, are now reared in captivity. Their popularity stems from their complex and highly modified morphological features and ornate coloration as well as the particular breeding habits of various species, in which there are elaborate courtship rituals and males fertilize the eggs and carry the young (in most species). Gasterosteiforms typically are not consumed as food fishes, but some syngnathids are commercialized heavily as curios. In particular, seahorses and seamoths are made into souvenirs (even as Christmas ornaments) and used as ingredients in traditional Chinese and related East Asian medicines. Some 47 countries worldwide participate in the seahorse market, and the total global consumption of seahorses in 1995 was at least 20 million specimens, roughly more than 62 tons (56 metric tonnes). The seahorse trade is not sustainable as it is currently implemented, leading to fears that many populations of seahorses have been exploited past the possibility of recovery.

Species accounts

List of Species

West Atlantic trumpetfish

Aulostomus maculatus

family

Aulostomidae

taxonomy

Aulostoma maculatum Valenciennes, 1837, West Atlantic.

other common names

None known.

physical characteristics

The trumpetfish is slender and elongate. The head is about one-third of the total length; the snout is tubular and the mouth large, terminal, and very upturned. The chin has a prominent barbel, and the eyes are relatively small and round. Single dorsal fin is preceded by eight to 13 short, well-spaced spines. Dorsal fin with 21–25 rays; anal fin opposite to dorsal fin and also with 21–25 rays; pelvic fins very posterior. Scales small and somewhat abrasive. Reaches at least 35.4 in (90 cm) in length. Coloration varies. May have dusky brown or reddish background with lighter stripes and darker spots, but some individuals are yellow or green with a blue snout.

distribution

Western Atlantic from Florida to southeastern Brazil; also in the Caribbean, Gulf of Mexico, Bermuda, and Antilles. Found in the eastern Atlantic at Saint Paul's Rocks.

habitat

Adults usually are found in coral reefs and associated habitats, at depths ranging from 6.6 to 82 ft (2–25 m); juveniles live in deeper water but also among sargassum.

behavior

Trumpetfishes may hover in near vertical positions, with their heads pointing downward, sometimes almost motionless. They align their bodies with other linear objects, ranging from corals to other fishes to crevices, blending in with their surroundings. They also are capable of quick movements. Reported to change color according to their habitat. They also use larger nonpiscivorous fishes such as parrotfish as mobile blinds, hiding behind them to approach within striking distance of prey.

feeding ecology and diet

Eats mostly smaller fishes and small invertebrates by employing stealthy movements and suction feeding (pipette feeding). May feed on larger fishes as well.

reproductive biology

Mostly unknown; juveniles are known to inhabit deeper waters, but eggs and larvae probably are pelagic.

conservation status

Not listed by the IUCN.

significance to humans

Sometimes kept in public aquaria. A harmless fish, sometimes marketed locally but of minor commercial importance.

Common shrimpfish

Aeoliscus strigatus

family

Centriscidae

taxonomy

Amphisile strigata Günther, 1861, Java, Indonesia.

other common names

English: Razorfish.

physical characteristics

A very unusual species, with an elongate, highly compressed body. Snout long, almost filamentous, with a terminal mouth. Dorsal fin terminal, situated far posterior, with a long, posteriorly directed and hinged spine followed by two smaller spines and nine to 10 rays. Caudal fin underneath dorsal fin. Anal fin with 11–12 rays; pectoral fin with 11–12 rays. Body covered in plates. Coloration yellowish dorsally and laterally above a dark, horizontal stripe that runs through the eyes; white underneath stripe and ventrally. Reaches 5.5 in (14 cm) in length.

distribution

Widespread in the tropical western Pacific Ocean and northern Indian Ocean, reaching as far west as the Seychelles.

habitat

Usually found in shallow bays, coral reefs, and sea grass beds down to a depth of about 66 ft (20 m).

behavior

Commonly encountered in large schools, typically hovering with its mouth pointed toward the bottom, maintaining a vertical position. Sometimes found in association with long-spined sea urchins of the genus Diadema.

feeding ecology and diet

Feeds on small invertebrates (e.g., polychaetes), including larvae of mollusks and crustaceans.

reproductive biology

Mostly unknown. Pelagic larvae have been described and begin to resemble adults by about 0.7 in (17 mm) in length.

conservation status

Not listed by the IUCN.

significance to humans

Not consumed but sometimes kept in aquaria.

Blue-spotted cornetfish

Fistularia tabacaria

family

Fistulariidae

taxonomy

Fistularia tabacaria Linnaeus, 1758, North Atlantic.

other common names

None known.

physical characteristics

An unmistakable species, with an extremely elongated body and snout (about one-fourth of the body length). Oblique terminal mouth with many minute teeth. Eyes elliptical and large. Small, single, and triangular dorsal fin located far posterior on the back, opposite to the anal fin and with 13–18 rays. Anal fin also triangular, with 13–17 rays. Pectoral fins have 15 or 16

rays. Very small pelvic fins. Caudal fin has two clear forks, with upper and lower lobes divided by a long caudal filament (formed from caudal rays, about as long as the snout). Coloration is greenish brown, with numerous blue spots and some 10 darker cross bars. Caudal filament is blue (coloration can change quickly to mach the background). Reaches up to 5.9 ft (1.8 m) without the caudal filament.

distribution

Occurs in both sides of the tropical and warm temperate Atlantic Ocean. Young are reported to venture into colder temperate waters as far north as Nova Scotia in the Western Atlantic.

habitat

A mostly inshore species, occurring down to 656 ft (200 m); adults are found in coral reefs and sea grass meadows, over sandy and rocky bottoms, and even in estuaries.

behavior

Mostly unknown. This species does not seek camouflage by aligning itself with objects, as does the trumpetfish. Usually solitary.

feeding ecology and diet

Eats mostly small shrimps and other fishes, which it can swallow whole, head first (by sucking them in a mode known as pipette feeding). Preyed upon by larger bony fishes (e.g., groupers) and sharks.

reproductive biology

Little is known of its reproductive biology, but other species of Fistularia lay pelagic eggs in open waters; larval development probably is pelagic as well.

conservation status

Not listed by the IUCN.

significance to humans

Not frequently consumed but a popular aquarium species.

Threespine stickleback

Gasterosteus aculeatus

family

Gasterosteidae

taxonomy

Gasterosteus aculeatus Linnaeus, 1758, Europe.

other common names

None known.

physical characteristics

Head relatively small, with small upturned mouth anterior to the eyes; eyes round and somewhat large. Body about four times as long as it is deep, with slender caudal peduncle. Three strong spines precede the first dorsal fin (with 10–14 rays), the last of which is smaller and attached to the dorsal fin; the first two spines are very tall. Dorsal spines are widely spaced. Anal fin opposite soft dorsal fin, with one spine and eight to 10 rays. Pectoral fins ending at mid-body length, with 10 rays. Pelvics have strong spine and single ray. All spines can be locked into place or depressed. Caudal fin brush-shaped. Trunk covered by slender plates, with much variation in arrangement. Coloration silvery on sides and bluish black dorsally, with orange pelvic membranes. Males become more reddish when courtship commences and drab when it terminates. Reaches 3.5 in (90 mm) in length.

distribution

Widely distributed in temperate marine waters of the Northern Hemisphere but also in coastal rivers and lakes.

habitat

The threespine stickleback occurs in a wide variety of coastal habitats in both brackish and shallow marine waters. It can be captured occasionally in the open ocean as well. Typical habitats include tidal pools, coastal rivers and creeks, lakes, salt marshes, and protected coastal inlets. Adults typically are found in association with vegetation (e.g., eelgrass). Individuals may venture far out into the open oceans, as far as 621 mi (1,000 km) in the Pacific.

behavior

Many populations remain most of the time in the open sea, venturing into coastal habitats to spawn and die in their second or third years. They swim by "rowing" with their pectoral fins and are capable of strong swimming motions, such as those required to ascend rivers. Moderately social outside of periods of reproductive activity, when males become strongly territorial.

feeding ecology and diet

Eats a wide variety of invertebrates and larvae, including copepods, gammarids, rotifers, branchiurans, oligochaetes, insects and their larvae, and even eggs of other sticklebacks. Sticklebacks are preyed upon by numerous other fishes as well as water birds, such as herons, mergansers, gulls, and loons.

reproductive biology

The reproductive biology of this species has been studied in detail. Females from 2 to 2.8 in (5–7 cm) in standard length have between 116 and 838 eggs, measuring about 0.06 in (1.5 mm) in diameter; egg number increases with body weight. Before spawning, males establish a territory, building a nest on the substrate (which is accomplished by "gluing" together bits of vegetation with mucus and kidney secretions). The nest is complete when the male carves out a tunnel, at which time courtship begins. A dance is performed for a gravid female that has entered the territory, which consists of the male jumping toward and away from the female in a zigzag fashion, with spines erect and mouth open. Once a female is impressed, the male exhibits gluing behavior and fans the nest with his pectoral fins. He then zigzags back to the female, leads her to the nest, and points to it with his open mouth. The female enters the nest with her caudal peduncle protruding, allowing the male to begin quivering movements against her flank. After she has deposited her eggs, the male moves through the nest, fertilizing the eggs and expelling the female. He then pushes the eggs deeper into the nest, flattening the egg mass and repairing the nest at the same time, before fanning the eggs. The male attempts to induce other females to spawn in the same nest; the number of female partners may vary, but studies conducted in Quebec indicated that males having two or three female partners is the norm in that region. Incubation lasts roughly 14–20 days. After the eggs hatch, the male destroys the nest and guards the young (collecting any that may have fallen away). After his progeny become free-swimming, the male starts another courtship cycle.

conservation status

Not listed by the IUCN.

significance to humans

Not a commercially important species. The threespine stickleback is studied intensely by fish ethologists. Often kept in aquaria, where it reproduces easily.

Armored stickleback

Indostomus paradoxus

family

Indostomidae

taxonomy

Indostomus paradoxus Prashad and Mukerji, 1929, Lake Indawgyi, Myanmar.

other common names

None known.

physical characteristics

Body elongate and slender, with a spatulate snout and terminal mouth. Eyes large and round. The single dorsal fin contains six rays, is located at mid-body length, and is preceded by five short and evenly spaced spines. The anal fin is opposite the dorsal fin, also with six rays. The caudal fin contains 11 rays and is rounded posteriorly. Pelvic fins are very small and thoracic, with only four rays. The precaudal tail region is very long and slender. Large pectoral fins have 23 rays. Body is covered by a complex armor composed of numerous plates. Coloration is a light brown, with numerous small, darker blotches and irregular stripes. Reaches 1.2 in (3 cm) in length.

distribution

Northern Myanmar, possibly to Cambodia.

habitat

Rivers and lakes of northern Myanmar, including the Ayeyarwaddy River and Lake Indawgyi. Occurs close to the bottom in canals, swamps, ditches, and stagnant waters.

behavior

Mostly unknown. This species apparently is sedentary in river or lake beds and moves about slowly.

feeding ecology and diet

Feeds mostly on worms and other small, slow-moving benthic invertebrates. Predators are presumably larger fishes.

reproductive biology

The reproduction of this species has been observed under captive conditions. Males defended spawning sites of a few centimeters inside a tube and had a lighter reddish brown coloration (instead of the typical darker brown color of nonbreeding males). There is sexual dimorphism in the pelvic fins: males have longer and wider pelvics with inward curving rays. Males displayed by erecting their fins and shaking their tail regions. Females are lighter brown during spawning, with bulging abdomens due to the presence of eggs. Females approached the nesting sites of the male when they were about to spawn (indicated by their protruding genital papillae) and were encouraged to enter the tube by the male. The upside-down female deposited eggs, usually on the roof of the tube; the male fertilized the eggs while also upside-down. Spawning may take several hours, and the male guards the nest. From five to

40 elliptical eggs were laid at a time, measuring about 0.08 in by 0.04 in (2 by 1 mm). Eggs hatched three days after spawning, and larvae were free-living four days after hatching, at about 0.14 in (3.5 mm). Larvae have an attachment organ on the tip of the yolk sac. Larval coloration is unique, composed of three black vertical bands, and adult coloration is attained after more than four weeks and at about 0.3 in (8 mm) in length.

conservation status

Not listed by the IUCN.

significance to humans

Occasionally imported as an aquarium species.

Longspine snipefish

Macroramphosus scolopax

family

Macroramphosidae

taxonomy

Balistes scolopax Linnaeus, 1758, Mediterranean Sea.

other common names

None known.

physical characteristics

Body is compressed laterally, with an elongated, tubular snout that terminates in a small upturned mouth lacking teeth. Eyes are round and large, with a single nostril on each side. Two dorsal fins, originating far posteriorly. First dorsal has extremely elongated and serrated second spine (four to eight spines, with each spine about as long as the snout); second dorsal fin has soft rays (10–14). Anal fin has 19–21 rays, pectoral fin has 18–21 rays, and pelvic fins have a single spine and four rays. Scales are very small. Pinkish or reddish dorsally; color fades to silvery on the sides. Reaches 9.1 in (23 cm) in total length.

distribution

Distributed worldwide, mostly in temperate latitudes.

habitat

Present mostly on the continental shelf in depths ranging from 164–902 ft (50–275 m). Juveniles are more pelagic, whereas adults are more demersal.

behavior

Forms large schools, mostly while juvenile. Individuals may hover with their mouths pointing down toward the substrate, remaining in a stationary position.

feeding ecology and diet

Feeds on invertebrates, including copepods and other crustaceans, mollusk larvae, foraminifera, polychaete eggs, and mysids. Preyed upon by larger fishes, including tunas and blue sharks.

reproductive biology

Eggs and larvae are pelagic, as are juveniles until they reach about 2 in (5 cm) in length. Adults are more demersal. In the eastern Atlantic, snipefish spawn on the continental shelf, over seamounts, and near islands between October and March. Larvae and juveniles remain in the surface layers during the day but migrate vertically to deeper water at night. At about 2 in (5 cm), some three months old, individuals move closer to the bottom.

conservation status

Not listed by the IUCN.

significance to humans

Not very important commercially, although it is consumed in the eastern Atlantic. This species has been kept in public aquaria.

Sculptured seamoth

Pegasus lancifer

family

Pegasidae

taxonomy

Pegasus lancifer Kaup, 1861, Australia.

other common names

None known.

physical characteristics

Snout very slender but not very elongated (longer in males), ending in a spatulate tip; snout clearly demarcated from head and bearing four spiny ridges. Eyes large and round. Mouth small and protrusible, located ventral to the snout base. Head triangular anteriorly. Head and trunk regions are depressed and broad (broader in females), encased in fused bony plates that bear prominent ridges forming a star pattern. Single dorsal fin posterior to the trunk, with five rays; opposite anal fin also has five rays. Tail long and slender, with bony ridges, ending in a truncate caudal fin with eight to nine rays. Pectoral fins very wide and fanlike when expanded, with 18 rays. Pelvics resemble hooks, with one spine and three rays. Coloration sandy-brown or grayish above, with darker spots on pectorals, a dark longitudinal stripe on the trunk, and a dark stripe at base of the tail; pale underneath. Reaches about 4.7 in (12 cm) in length.

distribution

Restricted to southern Australian waters from South Australia to Tasmania.

habitat

A bottom-dwelling species occurring in many different coastal habitats, including estuaries, sea grass beds, and sandy bottoms, down to about 180 ft (55 m).

behavior

This species can change its color to match that of its surroundings. It also can burrow into the substrate to escape predators. It often "walks" or "crawls" over the bottom in search of small crustaceans or other food items. Many individuals may congregate in estuaries.

feeding ecology and diet

Eats a variety of small invertebrates, such as polychaetes, mollusks, and crustaceans. Their mouths are somewhat protrusible,

enabling them to snatch prey from the bottom with ease. Presumably eaten by larger fishes.

reproductive biology

Enters sandy bays to breed in the spring, when courtship takes place. During courtship, a female and male remain on the bottom, side by side, until they rise together to spawn, vent to vent, about 3.3 ft (1 m) off the bottom. The posterior tips of the pectoral fins of males become yellow during the reproductive period. The eggs are pelagic, and larvae up to 0.1 in (2.5 mm) are enclosed in a dermal sac, probably an adaptation to a pelagic existence.

conservation status

Listed as Data Deficient by the IUCN.

significance to humans

Not a commercial species.

Ornate ghost pipefish

Solenostomus paradoxus

family

Solenostomidae

taxonomy

Fistularia paradoxa Pallas, 1770, Indonesia.

other common names

English: Harlequin ghost pipefish.

physical characteristics

A morphologically remarkable fish. Body is very slender and straight, and head is very elongate, about one-third the total length. Mouth terminal, small, and upturned. Eyes round. First dorsal fin situated over pelvic fins, with five very long spines; second dorsal fin more posterior, with 17–23 rays. Anal fin opposite second dorsal, with 17–22 rays; pectoral fins inconspicuous, with 24 rays; pelvic fins located just anterior to the middle of the body, with seven rays; caudal fin large and spur-shaped when rays are extended. There are numerous dermal projections on snout, trunk, and tail. Body encased in 31–35 segmented bony plates. Coloration spectacular and ornate. Background color varies from white or semitransparent to black, with elaborate pattern of red, orange, white, or yellow spots, blotches, and stripes. Reaches some 4.7 in (12 cm).

distribution

Present in much of the Indo-West Pacific Ocean from the Red Sea and East Africa to the Marshall Islands and New Caledonia; occurs as far north as southern Japan and as far south as Australia.

habitat

Usually found in coral reef habitats (down to about 115 ft, or 35 m, in depth) among gorgonian corals, weeds, and algae or with crinoids over sand, along reef edges, or in sheltered coastal waters and estuaries.

behavior

Typically a solitary species, but small groups of up to six individuals have been observed. This species is highly camouflaged, blending in very well with many different backgrounds. Young are mostly pelagic, but adults are more benthic; post-pelagic specimens are more transparent. Individuals may hover in a near vertical position when they are among gorgonians or other substrates.

feeding ecology and diet

Feeds on mysids, small shrimps, and other benthic crustaceans. Predators unknown but presumably larger reef-dwelling fishes.

reproductive biology

In contrast to other syngnathoids, females carry the brood in a pouch that is formed by the enlarged pelvic fins (which are missing from other syngnathoids). Eggs are numerous, small, spherical, and somewhat transparent. Females fan the eggs by opening and closing their pelvic fins. Young are expelled from the pouch at birth. Other details concerning their reproduction are unknown.

conservation status

Not listed by the IUCN.

significance to humans

Sometimes kept as an aquarium fish; otherwise this species has no commercial value.

Ringed pipefish

Doryrhamphus dactyliophorus

family

Syngnathidae

taxonomy

Syngnathus dactyliophorus Bleeker, 1853, Indonesia.

other common names

English: Banded pipefish.

physical characteristics

A very slender species, with both head and body on the same plane. Snout very slender, about one-eighth of the total length, with small upturned terminal mouth. Eyes round and relatively long. Single posterior dorsal fin, with 20–26 rays; small anal fin with four rays. Body has 15–17 bony rings, and tail has 18–22 bony rings. Caudal fin is round when expanded. Coloration composed of alternating black to reddish and yellow bars; caudal fin is white with a red circle. Reaches some 7.1 in (18 cm) in length.

distribution

This species is present throughout much of the Indo-West Pacific, in the Red Sea and East Africa to Samoa, and throughout Micronesia.

habitat

Inhabits a wide variety of coastal habitats, such as coral reefs, tide pools, lagoons, estuaries, sea grass meadows, and outer reef slopes. Frequently found in crevices and sheltered areas.

behavior

A cryptic species, preferring to remain in caves or other shelters. Commonly seen in pairs, but occasionally large groups are formed. Young are pelagic and transparent (up to about 1.2 in, or 30 mm) and attain adult coloration only later, when they settle into a more benthic lifestyle.

feeding ecology and diet

Eats small crustaceans and may even clean larger fishes, such as morays, of small parasites. Consumed by larger fishes.

reproductive biology

Males carry the eggs along their trunks ventrally. The eggs are small and spherical and reddish when fresh. The eggs are fertilized upon deposition on the male and hatch after a few weeks. Juveniles often are found in rock pools but typically are pelagic.

conservation status

Listed as Data Deficient by the IUCN.

significance to humans

A popular aquarium species, which has been reared in captivity.

Lined seahorse

Hippocampus erectus

family

Syngnathidae

taxonomy

Hippocampus erectus Perry, 1810, West Indies.

other common names

English: Seahorse.

physical characteristics

Body erect and somewhat sinuous, with head at a right angle in relation to the trunk and tail. Snout moderately long, with small upturned mouth devoid of teeth. Eyes round. Two pairs of spines present behind the eyes on the head. Small pectoral fins with 14–17 rays; single posterior dorsal fin with 16–20 rays; small anal fin with three to four rays; no pelvic fins. Prehensile tail tapers into a slender stalk without a caudal fin. Trunk encased in 10–12 bony rings, each with four spines; tail has 32–38 rings. Coloration varies widely—background light brown, black, gray, or yellow (sometimes red) with various small blotches, stripes, and spots. Area around the eyes has small white stripes radiating from the eyes. Reaches 7.9 in (20 cm) in length.

distribution

Western Atlantic from Cape Cod (sometimes Nova Scotia as strays) to Uruguay. The extensive range suggests that the name H. erectus may be applied to a complex of closely related species.

habitat

Lined seahorses are found in habitats with heavy vegetation, such as seaweeds and sargassum, in shallow waters and waters as deep as 240 ft (73 m). Present also in bays, piers, beaches, salt marshes, oyster beds, and other environments in which vegetation and shelter are present. They are capable of tolerating great variations in temperature and salinity.

behavior

Seahorses swim slowly, in a vertical position, by undulating the dorsal and pectoral fins and tend to cling with their prehensile tails to vegetation, gorgonian corals, and so forth. They produce sounds to communicate with each other. Younger individuals tend to be pelagic, sometimes swimming in groups.

feeding ecology and diet

Food consists mostly of small crustaceans, such as copepods, amphipods, and larvae. They employ pipette feeding, after a swift sucking action following a sudden upswing of the head. They are eaten by many species of bony fishes, including cod, bluefish, remoras, and spiny and smooth dogfishes.

reproductive biology

Between 250 and 400 eggs are deposited in the male's brood pouch during courtship (the larger the female, the greater the number of eggs). Males develop brood pouches by about 3 in (7.5 cm) in length, and males with eggs are recorded at 3.5 in (9 cm). In courtship the male and female closely follow each other, and the male presents his pouch to the female's genital area. As eggs are being transferred from the female into the male's pouch, they both rise in the water and may change color. Breeding takes place in the summer or year-round in tropical climates. Females deposit a few eggs at a time repeatedly. The eggs develop in the brood pouch and may derive nourishment from secretions within the pouch. Eggs are pear-shaped and light orange in color and may contain one or more oil droplets. Eggs are incubated for 12–14 days in the pouch; there is no true larval period; miniature seahorses are expelled, measuring about 0.24 in (6 mm) in length. Their tails become prehensile after one day, and they become mature after three months.

conservation status

Listed as Vulnerable by the IUCN.

significance to humans

A common aquarium species whose commercialization requires monitoring.

Leafy seadragon

Phycodurus eques

family

Syngnathidae

taxonomy

Phyllopteryx eques Günther, 1865, South Australia.

other common names

None known.

physical characteristics

One of the most distinctive of all fishes, the leafy seadragon has numerous, complex leaflike dermal projections from the extremities of its head, trunk, and tail spines. Body is elongate, slender but somewhat sinuous, and encased in ringlike bony plates that extend as spines. The head is long, directed at almost a right angle in relation to the body, with a frontal bony projection and an extremely elongated snout. The mouth is upturned and terminal. Eyes round. Dorsal fin, which is poseterior, has 34–38 rays; pectoral fins have 19–21 rays; anal fin has four rays. Tail slender and prehensile, with leaflike dorsal projections. Pelvic and caudal fins, lateral line, and scales are absent. Coloration is greenish brown or yellow, with vertical stripes along the trunk. Head has slight mask and varying dark blotches on leaflike projections. Specimens in deeper waters (about 98 ft, or 30 m) tend to be more reddish. Reaches some 13.8 in (35 cm) in length.

distribution

Coastal regions of southern Australia from Western Australia (below Perth) to southern Victoria.

habitat

A marine species inhabiting shallow (down to about 98 ft, or 30 m), temperate waters, usually sheltered among algae and reefs but also found over sandy areas.

behavior

A sluggish species, appearing to float aimlessly in kelp beds, protected by its elaborate camouflage. It may move rhythmically back and forth in a manner similar to algae being swept by currents. Adults may congregate in shallow bays in late winter to pair and mate. Divers can approach this species slowly. Cleaner shrimp and clingfish have been observed to "clean" parasites off leafy seadragons.

feeding ecology and diet

Feeds mostly on mysids and other crustaceans (e.g., shrimps and squad-lobsters). Predators unknown but presumably larger fishes.

reproductive biology

Reproduction has been observed in the wild in this species. (Aquarium-bred specimens take some two years to reach adult size.) Females have greatly swollen trunks before spawning. Males carry a brood containing an estimated 250–300 elliptical eggs underneath their tails, posterior to the anal fins. The eggs, which measure 0.3 by 0.2 in (7 by 4 mm), are maintained in honeycomb-like egg pockets in the abdominal skin of the males. Pregnant males usually are seen in November or December. The tail of the male becomes swollen and turns bright yellow to indicate readiness to mate, at which time sperm are released into the abdominal region. The courtship ritual is similar to that of some pipefishes (in which the abdominal area is displayed to the mate, while the head is maintained in an upright position). The female deposits her eggs onto the abdominal region of the male, pushing them into place. At that point, egg pockets form on the male to fasten the eggs securely in place. Incubation takes about eight weeks. Males deposit hatchlings in a wide area, as hatching takes about one week. Hatchlings are advanced and settle on the bottom (at about 1.4 in, or 35 mm, in length), sometimes remaining in small groups and venturing into shallower water.

conservation status

Listed as Data Deficient by the IUCN.

significance to humans

An aquarium species that also attracts numerous recreational divers who want to see it up close (e.g., in Victoria Harbor, South Australia). This species cannot be collected off South Australia legally. It is somewhat difficult to maintain in aquaria, owing to its specialized feeding requirements, but aquarium-raised specimens may live for more than 10 years in captivity. Many aquarium specimens are bred in captivity.

Weedy seadragon

Phyllopteryx teaniolatus

family

Syngnathidae

taxonomy

Syngnathus taeniolatus Lacepède, 1804, Bass Strait, Australia.

other common names

English: Common seadragon.

physical characteristics

Another remarkably distinct species. Body slender and elongate, highly arched between head and tail. Head at a slight angle to the body, with round eyes, very long snout, and small, upturned mouth. Encased in bony ringlike plates, many containing longer spines that have dermal leaflike flaps at the ends. Single dorsal fin situated posteriorly, with 27–34 rays; anal fin with four or five rays; pectorals with 20–23 rays. Tail prehensile, long, and slender, without a caudal fin; pelvic fins, lateral line, and scales absent. Coloration very ornate and somewhat varying— background usually reddish, with numerous closely packed yellow spots on head and body, bluish bars on sides of trunk and tail base, and darker dermal flaps. Reaches 18 in (46 cm) in length.

distribution

Southern Australian coast from central New South Wales to Rottnest Island (off Perth); also in Tasmania.

habitat

Typically found among algae, in kelp beds, and on rocky reefs, down to about 164 ft (50 m).

behavior

A mostly solitary species, hovering among algae and sheltered rocky reefs, but also seen over sand. Individuals may move into deeper waters when food becomes less abundant.

feeding ecology and diet

As with the leafy seadragon, food principally consists of small crustaceans. Predators unknown but presumably larger fishes.

reproductive biology

Many aspects of its reproduction are similar to that of the leafy seadragon. Males carry roughly equivalent numbers of eggs, which also are embedded in their skin. They usually have one brood per season, and mating begins from October to November. Young hatch after about two months, settling on the substrate. Hatchlings do not have the elongated snout of the adults, but it grows quickly; their elaborate dermal flaps are much smaller. Juveniles resemble adults by about 4.7 in (12 cm) in length.

conservation status

Listed as Data Deficient by the IUCN.

significance to humans

A popular aquarium species. Most specimens displayed are bred in captivity. They can live for more than 10 years in aquarium conditions.

Resources

Books

Allen, G. R. Marine Fishes of Tropical Australia and South-east Asia. Perth: Western Australian Museum, 1997.

Berra, T. M. Freshwater Fish Distribution. San Diego: Academic Press, 2001.

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Dawson, C. E. Indo-Pacific Pipefishes (Red Sea to the Americas). Ocean Springs, MS: Gulf Coast Research Laboratory, 1985.

Fritzsche, Ronald A. "Gasterosteiformes: Development and Relationships." In Ontogeny and Systematics of Fishes, edited by H. G. Moser, W. J. Richards, D. M. Cohen, M. P. Fahay, A. W. Kendall, Jr., and S. L. Richardson. Special Publication no. 1. Lawrence, KS: American Society of Ichthyologists and Herpetologists, 1984.

Gomon, M. F., J. C. M. Glover, and R. H. Kuiter, eds. The Fishes of Australia's South Coast. Adelaide: State Print, 1994.

Kuiter, Rudie H. Guide to Sea Fishes of Australia. London: New Holland, 1996.

——. Seahorses, Pipefishes and Their Relatives: A Comprehensive Guide to Syngnathiformes. Chorleywood, U.K.: TMC Publishing, 2000.

Leis, J. M., and D. S. Renis. "Centriscidae, Fistulariidae." In The Larvae of Indo-Pacific Coastal Fishes: An Identification Guide to Marine Fish Larvae, edited by Jeffrey M. Leis and Brooke M. Carson-Ewart. Leiden: Brill, 2000.

Lieske, Ewald, and Robert Myers. Coral Reef Fishes: Caribbean, Indian Ocean and Pacific Ocean: Including the Red Sea. Princeton, NJ: Princeton University Press, 1996.

Lourie, S. A., A. C. J. Vincent, and H. J. Hall. Seahorses: An Identification Guide to the World's Species and Their Conservation. London: Project Seahorse, 1999.

Masuda, H., K. Amaoka, C. Araga, T. Uyeno, and T. Yoshino. Nihon-san Gyorui Daizukan (The Fishes of the Japanese Archipelago). 2 vols. Tokyo: Tokai University Press, 1984.

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Orr, J. W., and T. W. Pietsch. "Pipefishes and Their Allies." In Encyclopedia of Fishes, edited by John R. Paxton and William N. Eschmeyer. San Diego: Academic Press, 1994.

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Smith, C. Lavett. National Audubon Society Field Guide to Tropical Marine Fishes of the Caribbean, Gulf of Mexico, Florida, the Bahamas, and Bermuda. New York: Knopf, 1997.

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Walker, H. J. "Aulostomidae." In The Larvae of Indo-Pacific Coastal Fishes: An Identification Guide to Marine Fish Larvae, edited by Jeffrey M. Leis, and Brooke M. Carson-Ewart. Leiden: Brill, 2000.

Periodicals

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Britz, Ralf, and Maurice Kottelat. "Two New Species of Gasterosteiform Fishes of the Genus Indostomus (Teleostei: Indostomidae)." Ichthyological Exploration of Freshwaters 10, no. 1 (1999): 327–336.

Dawson, C. E. "The Pipefishes (Subfamilies Doryrhamphinae and Syngnathinae)." Memoirs of the Sears Foundation for Marine Research 1, no. 8 (1982): 4–172.

Fritzsche, Ronald A. "A Review of the Cornetfishes, Genus Fistularia, (Fistulariidae), with a Discussion on Intrageneric Relationships and Zoogeography." Bulletin of Marine Science 26, no. 2 (1976): 196–204.

——. "A Revisionary Study of the Eastern Pacific Syngnathidae (Pisces: Syngnathiformes), Including Both Recent and Fossil Forms." Proceedings of the California Academy of Sciences 42, no. 6 (1980): 181–227.

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Johnson, G. D., and C. Patterson. "Percomorph Phylogeny: A Survey of Acanthomorphs and a New Proposal." Bulletin of Marine Science 52, no. 1 (1993): 554–626.

Kuiter, Rudie. "The Remarkable Sea Moth." Scuba Diver 3 (1985): 16–18.

Lourie, S. A., J. C. Pritchard, S. P. Casey, S.-K. Truong, and A. C. J. Vincent. "The Taxonomy of Vietnam's Exploited Seahorses (Family Syngnathidae)." Biological Journal of the Linnean Society 66 (1999): 231–256.

Masonjones, H. D., and S. M. Lewis. "Courtship Behaviour in the Dwarf Seahorse, Hippocampus zosterae." Copeia 1996, no. 3 (1996): 634–640.

Orr, James W., and Ronald A. Fritzsche. "Revision of the Ghost Pipefishes, Family Solenostomidae (Teleostei: Syngnathoidei)." Copeia 1993, no. 1 (1993): 168–182.

Palsson, W. A., and T. W. Pietsch. "Revision of the Acanthopterygian Fish Family Pegasidae (Order Gasterosteiformes)." Indo-Pacific Fishes 18 (1989): 1–38.

Pietsch, T. W. "Evolutionary Relationships of the Sea Moths (Teleostei: Pegasidae) with a Classification of Gasterosteiform Families." Copeia 1978, no. 3 (1978): 517–529.

Sorbini, L. "The Cretaceous Fishes of Nardò. 1. Order Gasterosteiformes (Pisces)." Bollettino del Museo Civico di Storia Naturale Verona 8 (1981): 1–27.

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Vincent, A. C. J. "The Improbable Seahorse." National Geographic 186 (Oct. 1994): 126–140.

——. "Trade in Pegasids Fishes (Sea Moths), Primarily for Traditional Chinese Medicine." Oryx 31, no. 3 (1997): 199–208.

Vincent, A. C. J., and L. M. Sadler. "Faithful Pair Bonds in Wild Seahorses, Hippocampus whitei." Animal Behaviour 50(1995): 1557–1569.

Other

"Project Seahorse." (17 Feb. 2003). <www.seahorse.mcgill.ca/intro.htm>

Marcelo Carvalho, PhD