Transitioning  75-day-old Fringelip dragonet (Draculo pogognathus)

Synopsis

  • Juvenile Frindgelip dragonets (Draculo pogognathus) were raised from wild eggs. 
  • The larval duration was 80 days.
  • First culture record of a Draculo species.

Dragonets are a diverse group of small, bottom-dwelling marine fish. They primarily inhabit tropical and subtropical coastal and reef environments worldwide. With around 180 species within the family Callionymidae, dragonets are known for their striking colors and unique appearances. Their diet consists primarily of small invertebrates such as crustaceans and mollusks. Dragonets’ intriguing mating rituals and captivating behaviors make them a subject of interest for marine enthusiasts and researchers, particularly in the Indo-Pacific region where they are most diverse and abundant. Notable genera within this family include Callionymus, comprising approximately 50 species and known for their elongated bodies and large, showy fins, and Synchiropus, consisting of roughly 30 species, cherished by aquarists for their vibrant patterns. The Dracula genus currently contains six species, all of which are known to burrow in sandy environments.

Draculo pogognathus, commonly named Fringelip dragonet or Hawaiian wonder dragonet, is currently only known to inhabit the Hawaiian Islands. It lives in clean sand off beaches in 1-4 m, burying just under the surface of the sand with the eyes exposed. Its secretive nature makes it difficult to observe, much less photograph, in its natural habitat. This species is also unique because it does not have a membrane connecting the inner pelvic ray to the pectoral-fin base and because it has a fringe of papillae on the lower lip.  The fringed lower lip serves to keep sand out during respiration. Females appear to attain a slightly larger size than males (Randall, 1999). At a maximum adult size of 3.2 cm, D. pogognathus is among the smallest known dragonets in Hawaiian waters.

Culture and Development

D. pogognathus juveniles were raised from eggs collected with a neuston tow made off Oahu’s south side in February 2020. The larvae were raised together with other larval fishes in a static 80L tank system on copepods. Isochrysis sp. was used to keep the copepods in the larval rearing tank healthy and nutritious. The larvae were transferred to a new tank when rearing conditions deteriorated and to assess mortality. Juveniles were grown out on artemia in an 80L tank with sand bottom attached to a recirculation system.

29-day-old Fringelip dragonet (Draculo pogognathus) undergoing flexion
29-day-old Fringelip dragonet (Draculo pogognathus) undergoing flexion

D. pogognathus larvae were first identified in the mix of larval species on 30 days post-hatch (dph), during flexion. Flexion D. pogognathus measure about 4 mm total length (TL) and have a yellow-colored cylindrical body and rounded head. A row of melanophores runs along the dorsal, middle, and ventral sides. The notochord tip is noticeably long, which is typical of dragonet larvae. An inconspicuous gas bladder lies just above a loosely coiled gut.

By 60 dph, D. pogognathus are about 10 mm TL. The head and body are more dorsoventrally flattened but still yellow and covered in melanophores. The rays on the fins are visible. Postflexion D. pogognathus larvae hover at an angle in the water column while feeding.

By 75 dph, the fish had grown to about 15 mm TL and finally showed the first obvious signs of settling (see header image). They were still seen in the water column, but they were also occasionally seen sitting on the bottom. The fins appeared fully developed. The eyes were large and had moved to a slightly more dorsal position. The dorsal and lateral body had taken on a metallic olive-green color while the ventral side is red. Over the next 7 days, the fish transitioned to juveniles.

Juvenile 82-day-old Fringelip dragonet (Draculo pogognathus)
Juvenile 82-day-old Fringelip dragonet (Draculo pogognathus)

Juvenile D. pogognathus have large eyes that face upward at an angle and a distinct fringed lower lip. The body is strongly dorsoventrally flattened and covered in scattered brown blotches. The belly is white. The dorsal fin is yellow. The juvenile fish look similar to the adults described by Randall (1999).

Conclusion

D. pogognathus larvae settle at a large size and have a long larval stage, making them challenging to raise compared to other dragonets. This, and the secretive nature of the juveniles, made the behavior of this fish particularly interesting to investigate. In an attempt to induce earlier settlement, smaller D. pogognathus larvae (from a previous mixed-species run) were moved to a larval tank with similar rearing conditions but with a sand bottom. However, the larvae did not show any signs of transitioning and did not survive. D. pogognathus is the fourth dragonet species raised for the Hawaii Larval Fish Project, after S. rubrovinctus, Callionymus decoratus, and S. corallinus.

Further Dragonet Aquaculture Research

Callionymus bairdi  (Lancer dragonet), Callionymus enneactis  (Mosaic dragonet), Synchiropus ocellatus  (Scooter blenny), Synchiropus picturatus (Spotted mandarin), Synchiropus splendidus (Green mandarin), Synchiropus stellatus  (Red Scooter Blenny) and Synchiropus sycorax (Ruby Red dragonet), Synchiropus circularis (Circled dragonet), Paradiplogrammus enneactis (Mangrove dragonet), Callionymus richardsonii (Richard’s dragonet), Callionymus valenciennei (Valenciennes’ dragonet) and Callionymus beniteguri (white-spotted dragonet) have all been aquacultured for research or the aquarium trade. 

References
  • Randall, John E., “Review of the dragonets (Pisces: Callionymidae) of the Hawaiian Islands, with descriptions of two new species.” (1999). Pac. Sci. 53(2):185-207. 
  • Randall, John E., 2007. Reef and Shore Fishes of the Hawaiian Islands. Sea Grant College Program, University of Hawai’i, Honolulu. i-xivb + 1-546.

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