Callionymoidei

(vertebrate zoology) A suborder of fishes in the order Perciformes, including two families of colorful marine bottom fishes known as dragonets.

(Dragonets and relatives)

Class: Actinopterygii

Order: Perciformes

Suborder: Callionymoidei

Number of families: 2

Evolution and systematics

Members of this suborder include the Callionymidae (the dragonets) and the Draconettidae (deepwater dragonets). As with many other perciform fishes, members of this suborder likely radiated in the Eocene period. The systematic placement of this suborder begs further consideration as it has been placed under the nonperciform order Gobiesociformes (Gosline, 1970; Leis and Carson-Ewart, 2000), or linked to the family Gobiesocidae in a closely related suborder, the Gobiesocoidei, within the Perciformes (Helfman et al., 1997).

The Callionymidae consists of at least 17 genera and 156 species, although exact numbers vary because of two different and competing classifications proposed by T. Nakabo (1982 and 1983) and R. Fricke (1983). The Callionymidae genera include:

• Anaora (one species)
• Bathycallionymus (two subspecies)
• Callionymus (82 subspecies)
• Calliurichthys (one species)
• Dactylopus (one species)
• Diplogrammus (six subspecies)
• Draculo (five subspecies)
• Eleutherochir (one subspecies)
• Foetorepus (eight subspecies)
• Neocynchiropus (two subspecies)
• Paracallionymus (one subspecies)
• Paradiplogrammus (two subspecies)
• Progogrammus (one species)
• Pseudocalliurichthys (three subspecies)
• Repomucenus (10 subspecies)
• Spinicapitichthys (one species)
• Synchiropus (29 subspecies)

The Draconettidae consists of only two genera, Centrodraco (10 subspecies, but one with 2 subspecies) and Draconetta (one species).

Physical characteristics

The Callionymidae are relatively small, sometimes diminutive, usually elongate fishes, having both a depressed trunk and broad or depressed head. Most of these fishes are sexually dimorphic. Males tend to have larger body sizes and dorsal fins, greater fin ornamentation, and more distinctive color patterns. Dragonets usually have 2 dorsal fins, the first containing 1–4 spines, the second has only 6–11 rays; the last ray is divided at the base, as in the anal fin. Dorsal fins of males may also be large or high, and also have elongated rays. Dragonets also have relatively large pelvic and pectoral fins, with the former positioned forward of the latter. The anal fin has 4–10 rays. The shape of the caudal fin varies, but may be elongate or spade-like and include elongated rays. The preoperculum has well-developed spines and bars along the margin, but no opercular or subopercular spines are present. Dragonets are further distinguished by the presence of small gill openings, generally pore-like, positioned at the top of the head or along the upper flanks, with gill membranes that are united at the isthmus that separates the gills. Their bodies lack scales, but their lateral lines are quite well developed. Many species have color patterns well suited as camouflage, but others are brilliantly, if not spectacularly, colored. Some species, such as members of the genus Foetorepus, produce an acidic, bitter-tasting slime that covers their bodies and may serve as a toxic deterrent to predators.

Dragonet larvae develop quite rapidly, and most species are able to settle with a full compliment of fins at a small size. The larvae are denoted mainly by having a relatively large head, a short snout that lengthens with growth, a small, protrusible mouth placed terminally on the head, the presence of teeth only after settlement, a large eye that migrates dorsally with growth, and a gas bladder located anterior to the gut, which disappears in adults. The gills are free from the isthmus at first but become attached after the larvae undergo flexion. The bodies of dragonet larvae are heavily pigmented, with most of the pigment concentrated on the ventral, rather than dorsal, surface of the body.

The Draconettidae have small, elongated, and rounded bodies, pointed snouts, relatively large pectoral fins, and elongated pelvic fins. The gill openings are relatively broad. There are two nostrils on each side of the head. Scales are absent, but the body is distinguished by the presence of a grooved or vestigial lateral line that is well developed on the head. These fishes are also distinguished by having large eyes. There are two dorsal fins, with three spines on the first and 12–15 rays on the second. There are 12–13 soft rays on the anal fin. The operculum and suboperculum have single strong spines but these are absent on the preopercle. Their larvae are very poorly known. The body is elongate and compressed, the head is also compressed and is of moderate size, the snout is pointed, and the mouth is small and reaches as far as the anterior margins of the large, round eyes. The gas bladder is absent, and the fin elements are present in larvae at least 0.31 in (0.8 cm) long.

Distribution

The Callionymidae are found in tropical and warm temperate waters of the Atlantic, Indian, and Pacific Oceans. Species are found at either continental or insular localities, however most species occur in the Indo-Western Pacific. The Draconettidae share approximately the same broad distribution, but are limited to seamounts or deeper edges of continental shelves, and thus live at cooler water temperatures.

Habitat

Most members of the Callionymidae are found on coral pavement, rubble, sand, mud, or on other soft bottoms. Some species occur exclusively in corals, tide pools, or among rocks; however, others may be found among algae-covered rocks on flats or shorelines, or mangrove roots in brackish water. The two species of the genus Bathycallionymus occur on deep flats. Members of the family occur within a depth range of less than 39 in (1 m) at low tide to over 1,312 ft (400 m). Little is known about the habitats of the Draconettidae. They may likely be found in rubble and sand or amongst rocks along deep-slope edges or on top of seamounts.

Behavior

The behavior of dragonets has been studied for only a few species and, for these, most effort has been directed toward reproductive behavior. Males utilize their longer first dorsal fins for displaying in both male-male aggressive encounters, and male-to-female social and courtship interactions. Male body color may also be utilized, especially during courtship.

Virtually nothing is known about the behavior of members of the Draconettidae. Their large eyes likely aid them in movement, feeding, social interactions, and reproductive behavior in deep demersal habitats. The dorsal fins of males may be utilized for signaling, but their effectiveness under dimly lit conditions remains to be demonstrated.

Feeding ecology and diet

Callionymids and draconettids feed on small benthic invertebrates. Larger species, such as members of the callionymid genera Callionymus, Foetorepus, Repomucenus, and Synchiropus), feed upon correspondingly larger prey. Predators of dragonets and draconets are not well known, but it is likely that they are preyed upon by larger benthic-feeding or opportunistic predatory fishes.

Reproductive biology

Dragonets appear to be gonochoristic, with no evidence of sex change reported. Males maintain relative large home ranges compared to females and these may be defended territorially during periods of reproduction. Mating systems may consist of pairs or single-male dominated mating groups of two or more females. Some smaller, cryptically colored males may also be in these mating groups and will attempt to court and spawn with females, but will often fail because of aggressive interactions with the dominant male. Courtship and spawning typically commences prior to sunset for most species or possibly just after dawn in some species. A male will approach a female and display his erect fins to her, and, as if carrying her, will ascend with her a short distance into the water column, where pelagic eggs are released and fertilized. These eggs are spherical in the genera Calliurichthys and Repomucenus, and in Callionymus from the Atlantic Ocean. The mangrove dragonet (Paradiplogrammus enneactis), and perhaps others in this genus, produces a buoyant egg mass that later breaks up prior to hatching. Spawning may be seasonal, depending upon latitude and water temperature, and may demonstrate one or more peaks during an annual cycle. Serial spawning, with the daily production of eggs during the season, has been suggested for some species. Smaller females of some species with bimodal spawning seasons may defer reproduction until the second season (late summer or autumn).

Next to nothing is known about the reproductive biology of the Draconettidae. Both the spawning mode and eggs are unknown. Owing to their close relationship with the Callionymidae, they are sexual dimorphic, with males being larger than females. They are not likely to be hermaphroditic. Spawning is probably paired and pelagic, with a rapid, short ascent into the water column where eggs and sperm are released.

Conservation status

One species of callionymid, the St. Helena dragonet (Callionymus sanctaehelenae), which is endemic to the island of St. Helena in the South Atlantic, is currently listed by the IUCN as Critically Endangered. Some callionymids important to the aquarium trade, such as the mandarinfish (Synchiropus splendidus) and Repomucenus spp. that are important as food fishes, may also be at risk from overfishing, habitat destruction, and recruitment failure as a consequence of pollution or the creation of anoxic conditions that lead to hypoxia among larvae. No members of the Draconettidae are listed by the IUCN, but these fishes may be at risk from the effects of the deep trawling of their habitats.

Significance to humans

A number of dragonet species are important in the aquarium trade, such as the mandarinfish, and some species, such as Repomucenus spp., are taken directly or as bycatch in commercial or subsistence food fisheries, or for the production of fish meal. The Draconettidae may be taken incidentally by deep-trawling fishing vessels, but appear not to have any commercial significance to humans.

Species accounts

Resources

Bohlke, J. E., and C. C. G. Chaplin. Fishes of the Bahamas and Adjacent Tropical Waters, 2nd edition. Austin: University of Texas Press, 1993.

Eschmeyer, W. N., ed. Catalog of Fishes, 3 vols. San Francisco: California Academy of Sciences, 1998.

Fricke, R. Revision of the Genus Synchiropus (Teleostei: Callionymidae). Braunschweig, Germany: J. Cramer, 1981. ——. Revision of the Indo-Pacific Genera and Species of the Dragonet Family Callionymidae (Teleostei). Braunschweig, Germany: J. Cramer, 1983.

Gloerfelt-Tarp, T., and P. J. Kailola. Trawled Fishes of Southern Indonesia and Northwestern Australia. Jakarta: Directorate General of Fisheries (Indonesia), German Agency for Technical Cooperation, Australian Development Assistance Bureau, 1984.

Helfman, G. S., B. B. Collette, and D. E. Facey. The Diversity of Fishes. Oxford: Blackwell Science, 1997.

Leis, J. M., and B. M. Carson-Ewart, eds. The Larvae of Indo-Pacific Coastal Fishes. Boston: Brill, 2000.

Masuda, H., K. Amaoka, C. Araga, T. Uyeno, and T. Yoshino, eds. The Fishes of the Japanese Archipelago. Tokyo: Tokai University Press, 1984.

Myers, R. F. Micronesian Reef Fishes. 3rd edition. Barrigada, Guam: Coral Graphics, 1999.

Nelson, J. S. Fishes of the World. 3rd edition. New York: John Wiley & Sons, 1994.

Randall, J. E., G. R. Allen, and R. C. Steene. Fishes of the Great Barrier Reef and Coral Sea, Revised and Expanded Edition. Honolulu: University of Hawaii Press, 1996.

Thresher, R. E. Reproduction in Reef Fishes. Neptune City, NJ: T.F.H. Publications, 1984.

Fricke, R., "Revision of the Family Draconettidae (Teleostei), with Descriptions of Two New Species and a New Subspecies." Journal of Natural History 26 (1992): 165–195.

Gosline, W. A. "A Reinterpretation of the Teleostean Fish Order Gobiosociformes." Proceedings of the California Academy of Sciences, 4, no. 37 (1970): 363–382.

Ikejima, K., and M. Shimizu. "Annual Reproductive Cycle and Sexual Dimorphism in the Dragonet, Repomucenus valenciennei, in Tokyo Bay, Japan." Ichthyological Research 45(1998): 157–164. ——. "Disappearance of a Spring Cohort in a Population of the Dragonet, Repomucenus valenciennei, with Spring and Autumn Spawning Peaks in Tokyo Bay, Japan." Ichthyological Research 46 (1999): 331–339. ——. "Sex Ratio in the Dragonet Repomucenus valenciennei." Ichthyological Research 46 (1999): 426–428.

Nakabo, T. "Comparative Osteology and Phylogenetic Relationships of the Dragonets (Pisces: Callionymidae) with Some Thoughts of Their Evolutionary History." Publications of the Seto Marine Biological Laboratory 28 (1983): 1–73. ——. "A New Species of the Genus Foetorepus (Callionymidae) from Southern Japan with a Revised Key to the Japanese Species of the Genus." Japanese Journal of Ichthyology 33 (1987): 335–341. ——. "Revision of the Genera of the Dragonets (Pisces: Callionymidae)." Publications of the Seto Marine Biological Laboratory 27 (1982): 77–131.

Randall, J. E. "Review of the Dragonets (Pisces: Callionymidae) of the Hawaiian Islands, with Descriptions of Two New Species." Pacific Science 53 (1999): 185–207.

Sadovy, Y., G. Mitcheson, and M. B. Rasotto. "Early Development of the Mandarinfish, Synchiropus splendidus (Callionymidae), with Notes on its Fishery and Potential for Culture." Aquarium Sciences and Conservation 3 (2001): 253–263.

IUCN/SSC Coral Reef Fishes Specialist Group. International Marinelife Alliance-University of Guam Marine Laboratory, UOG Station, Mangilao, Guam 96913 USA. Phone: (671) 735-2187. Fax: (671) 734-6767. E-mail: donaldsn@uog9.uog.edu Web site:

[Article by: Terry J. Donaldson, PhD]