Synopsis

  • The Exclamation point dragonet (Synchiropus corallinus) was raised from wild collected eggs at 78-80F on copepods.
  • The larval duration was 30 days.
  • First record of Exclamation point dragonet culture.

Background

Dragonets (Callionymidae) are small to medium (2 – 30 cm), slender, scaleless, slow-moving, benthic fishes, comprising 18 genera/186 species. They are found in oceans worldwide but most species inhabit tropical and subtropical seas of the Indo-Pacific feeding on small benthic invertebrates on sand, coral, rubble or mud. The Synchiropus genus holds 44 species, including most of the colorful dragonets we keep in our aquariums (S. splendens, S. picturatus, S. stellatus, S. moyeri and S. ocellatus). 

Male Exclamation point dragonet (Synchiropus corallinus) in 50 feet of water off Oahu.

The Exclamation point dragonet is a little-known, cryptic Synchiropus species reported from Japan, New Caledonia, and Hawaii and, most recently, from Tonga from depths of 30-400 feet. Considered rare, this 1.6″/4 cm well-camouflaged fish might actually be more common than previously thought. When looking for Exclamation point dragonets off Oahu, I search unprotected sandy, coral rubble zones near coral reefs between 40 and 60 feet.   Finding them takes patience since they perfectly blend in with sand.  I like the molted color pattern of  the male and  its large, sail-like dorsal fin.

Culture and Larval Development 

S. corallinus juveniles were raised in 2018 and 2020 from a few eggs collected off Oahu’s south side.  On both occasions, the larvae were raised together with other larval fish species in a static 13 black round tank system on copepods (primarily Parvocalanus sp.). Isochrysis sp. was used to create turbidity and to enhance nutritional quality of the live foods in the larval rearing tank.

Exclamation point dragonets (Synchiropus corallinus) larvae raised in the laboratory (images are not to scale).

S. corallinus have tiny larvae, esp. in the early stages. Preflexion larvae measure just 2.9 mm TL (total-length) at 8 dph (days-post-hatch). 16-day-old larvae have passed through flexion but are still only 3.8 mm TL. S. corallinus larvae settled near day 30 at 6.3 mm TL. They develop a white dorsal surface as they metamorphose into juveniles. From 6-8 dph, when S. corallinus larvae were first detected in the mix of larval fishes, about one out of three individuals survived to become a juvenile.

Conclusion

S. corallinus is the third dragonet species raised for the Hawaii Larval Fish Project, after S. rubrovinctus and Callionymus decoratus. S. corallinus larvae are similar in size and morphology to S. rubrovinctus but are less red and more orange and settle 7-10 days later. The larvae appear relatively easy to raise on copepods, similar to S. rubrovinctus.

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) have all been aquacultured for the aquarium trade. Of these, S. splendidus is most consistently available.

References
  • Nakabo, T. 1991. Redescription of a rare callionymid fish, Paradiplogrammus corallinus, from Hawaii and Japan. Japanese Journal of Ichthyology, 38 (3): 249–253; Tokyo.
  • Randall, J.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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