Written by Kathleen Rader, CAS, The Daphian, January 1991
If you are looking for a small fish to put in your invertebrate, seahorse, or other salt water tank, take a close look at these little fish. Their natural curiosity, hopping motions, and ability to get in and out of very small crevasses will add spice to your tank watching, not to mention the addition of wild color patterns by some of these species.
Dragonets belong to the Callionymus family, which contains approximately eight genera and over one hundred species, all of which are marine. The four species most commonly seen in the United States belong to the genus Synchiropus, although some have been misnamed “goby” or “blenny”. Callionymus lyra, from the temperate waters off Europe, is one of the pioneering fish in marine aquarium keeping. The spawning behavior has been known since the 1800’s.
Dragonets live on the bottom of tropical and temperate coastal waters in sandy areas and along the borders of rocky areas. They are found both in shallow water and at considerable depths. Because of their habit of partially burying themselves in the substrate, they can be collected by sieving or seining the sand at low tide. In Hawaii, they have been observed in polluted harbors, scooting in and out from amount the tires and debris, and in clean back-water lagoons with small rock, live coral and a silt bottom. In the Philippines, they live in pairs or small groups in reefs and closely associated sandy areas between the reef crests.
Fish in this family are characterized by their small size (maximum size is 12” (20cm), but most are less than 4” (10cm), strong preopercular processes or spines which are covered with hooks and spines, and small rounded gill openings located toward the top of the broad, depressed head. The spines can be erected and used for defense. Protruding eyes are positioned high on the head. Adult fish are bottom dwellers. They can often be seen partially buried in the substrate. This is facilitated by the high position of the gill hole and eyes. Their small, pointed mouth contains teeth. They have large lips and a protractile upper jaw which can be thrust forward considerably to help them catch small crustaceans, etc.
Dragonets have two dorsal fins; the anterior one has weak, flexible spines. They use their oversized pectoral fins to “sit” on the bottom and to hover around. “Swimming” consists of a series of short hops during which they flutter their pectorals to attain movement. Their ventral fins are located well forward. The lateral line is visible in most species, but is obscure or lacking in a few. Dragonets like to maintain contact with the substrate and appear uncomfortable in open water.
Scales are absent, and dragonets are covered with a good deal of slime. Some authors suggest that this slime is toxic, bad smelling or bad tasting and is used as a defense mechanism, since it is strongly secreted when these little fish feel threatened. Other fish seem to leave dragonets alone. The thick layer of slime makes these little fish more resistant to parasitic diseases. If they do get sick, as for any scale-less fish, DO NOT treat with heavy metal-based medicines such as copper sulfate.
Gentle in nature, dragonets seem to get along with everyone except when two or more males of the same species are sharing a small tank with inadequate hiding places. During disputes with members of the same species, they intimidate each other by spreading their gill covers, thereby displaying their preopercular spine. Groups of one male and one or more females generally get along well, providing there is plenty of rock, coral, plants and so on for them to hide in. More than one male of the same species can be kept in large, well decorated tanks where there is sufficient room for each male to establish his own territory.
Males tend to be more robust, to have longer caudal and dorsal fins and to be more brilliant in color than females. In male S. splendid us (Mandarin Fish) and S. picturatus (Spotted Dragonet), the first spine in the anterior dorsal fin is very long. In some specimens, it reaches to the caudal peduncle when laid across the back. All of the rays of the first dorsal fin are elongated in males of S. stellatus and S. ocellatus (Scooter “Blenny”), and the skin between the rays has eyespots. When courting or threatened, males erect their dorsal fins.
Dragonet males seek out a female in the evening. The male initiates spawning by displaying his conspicuous dorsal fins. He then begins to move parallel to the female, gradually moving closer to her. The two then slowly swim upward in the water column with their bodies close together. The free-floating, spherical eggs are released and fertilized simultaneously. Spawning can become commonplace in a well planted or reef-type tank, with a pair spawning almost every night for several months straight. After releasing the pelagic eggs, the adults go their separate ways until the next night.
Eggs are easily recognized by the intricate pattern of intersecting lines which cross them, making them look almost like a geodetic dome. For success in raising fry, the free floating eggs should be collected. In 18 hours, S. splendid us eggs are approximately 0.004” (1mm) long with a prominent yolk sac. They remain in the plank tonic stage for at least two weeks, after which they take up residence in the bottom community. Some of the larvae are extremely small, too small for rotifers. Success has been achieved by feeding marine infusoria, especially copepod nauplii.
Dragonet eating habits have been compared to those of birds. They contemplate their food before eating. They are picky, slow, methodical eaters and therefore do not compete well for food. They feed on small crustaceans (mysids, amphipods, isopods and benthic copepods), worms and protozoan’s. Small fish need to eat more often than larger fish, so dragonets spend their day examining the substrate and surrounding live rock for food. In a well established invertebrate aquarium, they usually find enough micro-crustaceans to eat and do not need to be fed. Any food should be small enough for them to swallow and should sink to the bottom. They will come to the surface to eat if hungry. The Scotter “Blenny” that I kept with my seahorses did well on a diet of adult brine shrimp and small livebearers. Others have had luck feeding baby and adult brine shrimp, live Mysis shrimp, tubifex, Daphnia, freeze-dried food, or chopped clams, mussels or other meaty items.
CLASSIFICATION OF DRAGONETS
ORDER: Percifomes or Gobiesocofomes, depending on author
FAMILY: Callionymidae - 8 genera, over 100 species
C. Agassiz - Spot fin Dragonet
- Have been netted in water 300’ to 1500’ (91 to 457 m) deep off the coast of Florida.
C. bairdi - Lancer Dragonet
- From tropical western Atlantic (Virgin Islands); spine counts (D iv,9; A 8; P 19-20, C 15);
- Grow to 4” (10 cm), but usually only reach 2” (5 cm) in aquariums.
C. boeki - Coral Dragonet
C. lyra - European Dragonet
From the North Sea to the Mediterranean Sea in temperate waters, there are one of the pioneering fish in the salt-water aquarium hobby, having been successfully spawned prior to WWII. They do not do well above 20C (68F).
GENUS SYNCHIROPUS: 26 species, only 4 regularly kept in aquariums
S. ocellatus - Scotter “Blenny”
- From shallow water of the Indo-Australian archipelago.
S. picturatus - Psychedelic, Spotted or Oscellated Dragonet
- From water of the Philippines and New Guineas, maximum length 3” (7.6 cm).
S. splendid us - Mandarin fish or “goby”
- From tropical reefs of the Indo-Australian archipelago and Hawaii. Previously classified as Callionynus splendid us. Spine count: D iv, 9; A 8; P 29. Grows to about 3.5” (9 cm). maximum size 5” (12.7 cm). Have a wavy color pattern of green, blue, orange, purple and yellow. Eyes may be bright red encircled by blue. Males have more orange on their faces.
- Similar in appearance to the Scotter “Blenny,” S. ocellatus.
- Axelrod, H.R. and Burgess, W.E. (1987) Saltwater Aquarium Fishes, TFH Pub., 384 pp.
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- Burgess, W.E. (1972) Two Magnificent Colored Dragonets from the Philippine Islands, Tropical
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- Ostrow, M.E. (1979) The littlest Dragon Synchiropus splendid us, Tropical Fish Hobbyists (April), p 44-49.
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- Thresher, R.E. (1984) Reproduction in Reef Fish, TFH Publications, p. 334 & 335.
Reprinted from the Colorado Aquarist the official publication of the Colorado Aquarium Society, Autumn, 1990.