Dragonets | |
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Ocellated dragonet, Synchiropus ocellatus | |
Scientific classification | |
Kingdom: | Animalia |
Phylum: | Chordata |
Class: | Actinopterygii |
Order: | Callionymiformes |
Family: | Callionymidae Bonaparte, 1831 |
Type species | |
Callionymus lyra | |
Genera | |
See text |
Dragonets are small, percomorph, marine fish of the diverse family Callionymidae (from the Greek kallis, "beautiful" and onyma, "name") found mainly in the tropical waters of the western Indo-Pacific. They are benthic organisms, spending most of their time near the sandy bottoms, at a depth of roughly two hundred meters. There exist 139 species of the fish, in nineteen genera.
Due to similarities in morphology and behavior, dragonets are sometimes confused with members of the goby family. However, male dragonets can be differentiated from the goby by their very long dorsal fins, and females by their protruding lower jaws. The Draconettidae may be considered a sister family, whose members are very much alike, though rarely seen.
The following genera are classified within the Callionymidae: [1]
These "little dragons" are generally very colorful and possess cryptic patterns. Their bodies are elongated and scaleless. A large preopercular spine is characteristic of this fish, [1] and has been reported to be venomous in some species. All fins are large, showy and elongated; the first high dorsal fin usually has four spines; in males, the first of these spines may be further adorned with filamentous extensions. Dragonets have flattened, triangular heads with large mouths and eyes; their tail fins are fan-shaped and tapered.
The largest species, the longtail dragonet (Callionymus gardineri) reaches a length of 30 centimetres (12 in). At the other end of the spectrum, the Saint Helena dragonet (Callionymus sanctaehelenae) reaches a length of just 2 centimetres (0.79 in). Many species exhibit marked sexual dimorphism: males and females are coloured and patterned differently from each other, and (in addition to the spine filament) males have a much higher dorsal fin. This difference is extreme in the high-finned dragonet (Synchiropus rameus).
Dragonet spawning occurs during late afternoons, right before the sun sets. [2] The fish's spawning behavior is divided into four distinctive stages: courtship display, pairing, ascending, and the release of eggs and milt. [2] Both male and female dragonets have been observed displaying and courting each other, although the practice is much more frequent in the males. Females only do so when they are ready to spawn and are in need of a mate. [3] Both sexes display by spreading their pectoral and caudal fins, and moving around or by the side of the other sex. Males will sometimes also spread their dorsal fins, repeatedly open and close their mouths, and position themselves on top of the females and rub their abdomens with their bodies. If a female accepts a male for spawning, they form a pair. Occasionally, another male might intrude upon the pair as they are mating and attempt to sneak fertilizations with the female. Such an act would result in aggression by the original male. [4]
Prior to spawning, a male and female dragonet pair will ascend approximately 0.7-1.2 meters up a water column from the sand at the bottom of the ocean. [5] The male assumes a parallel position to the female, touching the female's side with the part of its body near its ventral fin. [5] The pair rises slowly up the water column, moving in a semicircular manner by swimming with their pectoral fins. [5] The ascent occurs in two phases. During the first phase, the dragonet pair moves upward about fifteen centimeters and rests for around five seconds. [5] Then it proceeds with its second rise. During this second phase of the ascent, the male and female flex their bodies and move their genital papillae toward each other. [5] The male releases its ejaculate and the female releases its eggs. The release of eggs occurs singly and continuously for approximately five seconds. [5] The eggs are pelagic, floating freely in the water column. [5] The female releases a high number of eggs during each spawning, and the dragonets do not guard their offspring. [5] The eggs are buoyant, so they intermingle with plankton and get swept away by the ocean current. [5] After the spawning, the dragonet pair parts from each other and swims back down to the ocean floor. Male dragonets are polygynous, and will begin to search for other females to repeat the mating process with. [5] They generally spawn with several different females within one reproductive day. Dragonets are very sexually dimorphic, with the males being much larger and having longer fins than the females. [6] This sexual dimorphism may have evolved in males in response to female mate choice, male-male competition, or both. [6]
Male dragonets form dominance hierarchies and act extremely aggressively towards each other. They are often observed chasing and biting, which occurs primarily when two males are close to a female during courtship and pairing. [3] Fights can be very intense; when one male recognizes another male near its breeding site, it will rush toward it and bite at its rival's mouth. The two may bite at each other and twist their bodies around one another for longer than a minute. [7] As a result of this behavior, male dragonets suffer higher mortality rates than females do after attaining maturation. [8] The highest mortality rates in adult males occur during breeding. Males have evolved larger bodies, as well as longer spines and rays, in order to achieve dominance in reproduction. They have also developed bright colors so as to more effectively compete for female attention. These secondary sex characteristics further reduce the survival potential of male dragonets, as they increase the risk of predation, require greater energy costs, and escalate the risk of suffering injuries. [5]
Feeding by the dragonet occurs throughout the day, including the intervals between courtships and spawning. The fish feeds entirely on benthic sources, primarily copepods, amphipods, and other small invertebrates living on blades of sea grass. [9] Species of dragonets from different locations show variations in specific food preference, attributable to the different availabilities and abundances of food organisms in those places. All of them feed by extending their highly protractible jaws toward their food and drawing it into the mouths, frequently followed by the expulsion of sand. No evidence suggests that dragonets are territorial. Individuals do not defend specific areas of substrate, as well as any resources that might be present on them, from intrusion by conspecifics or other fish species. [7]
Among Calliurichthys japonicus and Repomucenus huguenini, the two most abundant dragonet species, amphipods are the most plentiful prey during the spring and winter months. The fish also supplement their diets with polychaetes, bivalves, and gastropods in these periods. During the summer, the dragonets feed primarily on ophiuroids and amphipods. In this season, ophiuroids are the most dominant in number. Finally, in the fall, the two species predominantly consume polychaetes, amphipods, and gastropods, with polychaetes contributing the highest amount. [10]
Four types of swimming are observed in the dragonet. The first is burst swimming, the most common of the four, and utilized during foraging. The dragonet uses its pelvic fins to propel its body off of a substrate, and then its pectoral fins to guide itself forward. The second is continuous swimming, often utilized by males when approaching a potential mate or retreating during an aggressive encounter with another male. The dragonet uses its pectoral fins to propel its body forward, and its pelvic fins to lift and guide itself. The third type of swimming is rapid swimming, which is observed when the dragonet is attacking or fleeing. The fish primarily uses its caudal fins to achieve a quick speed. Finally, the fourth type is vertical swimming, utilized by the dragonet during spawning when it ascends. The pectoral fins are used to propel the fish's body up the water column. [7]
In defense against its predators, the dragonet rapidly buries itself under the sand at the bottom of the ocean so that only its eyes remain visible. Many species of the fish also are capable of producing and secreting foul-tasting and -smelling substances that may ward off any potential predators. [11]
Triggerfish are about 40 species of often brightly colored fish of the family Balistidae. Often marked by lines and spots, they inhabit tropical and subtropical oceans throughout the world, with the greatest species richness in the Indo-Pacific. Most are found in relatively shallow, coastal habitats, especially at coral reefs, but a few, such as the oceanic triggerfish, are pelagic. While several species from this family are popular in the marine aquarium trade, they are often notoriously ill-tempered.
Gobiidae is a family of bony fish in the order Gobiiformes, one of the largest fish families comprising more than 2,000 species in more than 200 genera, sometimes referred to as the "true gobies". Most of them are relatively small, typically less than 10 cm (3.9 in) in length. The Gobiidae includes some of the smallest vertebrates in the world, such as Trimmatom nanus and Pandaka pygmaea, Trimmatom nanus are under 1 cm long when fully grown, then Pandaka pygmaea standard length are 9mm (0.35 in),maximum known standard length are 11 mm (0.43 in). Some large gobies can reach over 30 cm (0.98 ft) in length, but that is exceptional. Generally, they are benthic, or bottom-dwellers. Although few are important as food for humans, they are of great significance as prey species for commercially important fish such as cod, haddock, sea bass, and flatfish. Several gobiids are also of interest as aquarium fish, such as the dartfish of the genus Ptereleotris. Phylogenetic relationships of gobiids have been studied using molecular data.
The bluegill, sometimes referred to as "bream", "brim", "sunny", "copper nose" or "perch" as is common in Texas, is a species of freshwater fish of the family Centrarchidae (sunfish) from the order Perciformes, native to North America and commonly found in streams, rivers, lakes, ponds and wetlands east of the Rockies.
The Zeidae are a family of large, showy, deep-bodied zeiform marine fish—the "true dories". Found in the Atlantic, Indian, and Pacific Oceans, the family contains just six species in two genera. All species are important and highly regarded food fish supporting commercial fisheries, and some—such as the John Dory —are enjoyed in large public aquaria. These fish are caught primarily by deep-sea trawling.
Synchiropus splendidus, the mandarinfish or mandarin dragonet, is a small, brightly colored member of the dragonet family, which is popular in the saltwater aquarium trade. The mandarinfish is native to the Pacific, ranging approximately from the Ryukyu Islands south to Australia. It can usually be found in some of the warmer waters.
The Japanese bullhead shark is a species of bullhead shark in the family Heterodontidae found in the northwestern Pacific Ocean off the coasts of Japan, Korea, and China. This benthic shark occurs at depths of 6–37 m (20–121 ft) over rocky bottoms or kelp beds. Measuring up to 1.2 m (3.9 ft) long, it can be identified by its short, blunt head, two high dorsal fins with anterior spines, and pattern of irregularly shaped, vertical brown bands and stripes. The Japanese bullhead shark is a docile, slow-swimming species that feeds mainly on shelled invertebrates and small bony fishes. Reproduction is oviparous, with females laying spiral-flanged eggs in communal "nests". This species is of little interest to fisheries.
Hoplosternum littorale is a species of catfish belonging to the Callichthyinae subfamily of the family Callichthyidae. It is known as tamuatá in Brazil, atipa in French Guiana, hassa in Guyana, kwi kwi in Suriname, cascadu or cascadura in Trinidad and Tobago, and busco or currito in Venezuela.
Callionymus is a genus of dragonets found mostly in the Indian and Pacific oceans with a few species occurring in the Atlantic Ocean.
The Japanese sea bass is a species of catadromous marine ray-finned fish from the Asian sea bass family Lateolabracidae which is found in the Western Pacific. In Japan this species is known as suzuki.
Callionymus belcheri, Belcher's dragonet or the flathead dragonet, is a species of dragonet native to the Pacific Ocean waters off of Australia and Papua New Guinea where it occurs at depths of from 18 to 36 metres.
Callionymus fasciatus, the banded dragonet, is a species of dragonet native to the Mediterranean Sea from the Gulf of Genoa to the western Aegean Sea. Also known from the southern and eastern Black Sea. It prefers sandy substrates where its diet consists of benthic invertebrates.
The common dragonet is a species of dragonet which is widely distributed in the eastern North Atlantic where it is common near Europe from Norway and Iceland southwards. It is a demersal species that occurs over sand bottoms. It lives to a maximum age of around seven years. It is caught in bycatch by fisheries and is used in the aquarium trade.
Callionymus maculatus, the spotted dragonet, is a species of dragonet native to the eastern Atlantic Ocean and the Mediterranean Sea where it occurs at depths of from 45 to 650 metres. This species is important to local peoples engaged in subsistence fishing.
Callionymus pusillus, the Sailfin dragonet, is a species of dragonet common in the Eastern Atlantic, where it occurs on the Portuguese coast to as far north as Lisbon and south to Morocco, and also in the northern Mediterranean including the Adriatic, Aegean and Black seas as well as the coastsLebanon and Israel. It occurs on the southern Mediterranean shore as far east as Tunisia Males of this species grows to a length of 14 centimetres (5.5 in) TL while females reach a length of 10 centimetres (3.9 in) TL. In the areas of the Mediterranean where it occurs it is one of the commonest dragonet species, as it is the only species that has been recorded within many protected areas. It is a benthic species which occurs in shallow waters and prefers sandy bottoms down to 100 metres (330 ft). The males are territorial, aggressively defend their territories from other males and like other dragonets this species undergoes complex breeding behaviour which has 4 phases. This starts with courtship, the male and female then form a pair before ascending to the surface where they release eggs and milt. The spawning season runs from May to August in the Mediterranean and the eggs and larvae are pelagic. This species feeds mainly on small benthic invertebrates such as worms and small crustaceans.
Lipophrys pholis, commonly known as shanny, also known as the smooth blenny or common blenny, is a species of combtooth blenny. It matures at two years of age. Distributed in the Eastern Atlantic from the southern Norway to Morocco and Madeira, including the Mediterranean and the Balearics. Lipophrys pholis feed primarily on crustaceans, but also feed on other invertebrates and plants.
Sebastes inermis, the Japanese red seaperch or dark-banded rockfish, is a species of marine ray-finned fish belonging to the subfamily Sebastinae, the rockfishes, part of the family Scorpaenidae. It is found in the northwestern Pacific Ocean.
Black kokanee, or kunimasu in Japanese, is a species of landlocked Pacific trout in Japan that was thought to be extinct for 70 years before being rediscovered in 2010. The species was originally endemic to Lake Tazawa, Akita Prefecture, but was translocated to Lake Saiko in an attempt to save the species. These efforts were only discovered to have been successful in 2010 when nine specimens were captured by a team of researchers including a celebrity biologist, 'Sakana-kun'.
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Synchiropus phaeton or the Phaeton dragonet is a species of bony fish of the family Callionymidae, the dragonets. It can be found in the Mediterranean and in the eastern Atlantic.
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