Last month I introduced you to a small genus in the Gobiidae family; a huge family that is found most anywhere bodies of saltwater are present. Due to the overall size and diversity of Gobiidae, I decided to continue exploring this family by discussing another small genus from the vast assortment of reef tank-suitable genera. The gobies of the genus Gobiodon, often called "clown gobies" or "gum drop gobies," are my fish of choice for October.

Meet the Family

Gobiidae is the largest family of marine fish with over 2,000 members and still growing. Gobiodon is a small genus within Gobiidae, comprised of only 15 recognized species (Harold & Winterbottom, 1995) (see below); though more than 30 nominal species have been described (Munday et al., 1999) including the recently classified Gobiodon brochus (Harold & Winterbottom, 1999).

A strange commensal relationship that doesn't exist in the wild, but regularly takes place in captivity. Gobiodon histrio seems to take a liking to Catalaphyllia jardinei in the home aquarium. Photo courtesy of Duane Dennis.

The reader may note the lack of G. brochus in the list above. Gobiodon brochus was not recognized during the most recent revision of Gobiodon (Harold & Winterbottom, 1995). A new revision is in preparation by the same authors, however, and it will include G. brochus as a valid species (Munday et al., 1999).

A typical looking Gobiodon citrinus. Note the location of the blue lines and black dot. Photo by Henry Schultz.

Individuals of Gobiodon species are small fish, rarely growing larger than 60mm. Though some species are predominantly scale-less, the majority of them are totally scale-less. Instead of scales, their smooth-sided skin has a thick, toxic mucus covering (Hasimoto et al., 1974). The jaws contain predominately small teeth, though two pairs of well-developed canine teeth are present. At least one species, Gobiodon brochus, has a modified jaw. The exact function of this modified, protruding, deflected lower lip is not known, although it has been suggested that it utilizes its extra "toothy pad" to rasp tissue from coral polyps (Winterbottom, pers. comm.). Gobiodon species are also equipped with modified ventral fins which have joined as one and developed small suction cups on the end. These aid the gobies in grasping onto corals in high current areas.

Gobiodon citrinus shows off its modified ventral fins. These are particularly useful in the high water currents associated with Acropora sp. Photo by Henry Schultz.

In the Wild

Gobiodon species are found throughout the Indo-Pacific, and some species extend to the Red Sea and to the western Pacific Ocean. They are abundant in these waters, and range from depths of 5 feet to as deep as 60 feet. Their depth distribution is directly dependant upon available corals within which they can find shelter. Generally speaking, though, the corals these fish inhabit are found in shallow waters.

Like many other gobies, species of Gobiodon partake in a special symbiotic relationship of their own. Fish of this genus are obligate coral dwellers, usually exhibiting a relationship known as "commensalism" with corals of the genus Acropora (Tyler, 1971), though some species relate with a few other corals, namely Echinopora spp., Hydnophora spp., and Stylophora spp. High upon the reefs, within the branches of these corals, the clown gobies will take refuge and wait for a passing morsel. Examination of the gut contents by Harold and Winterbottom (1999), found that these "passing morsels" were copepods, foraminifera, and unidentifiable flocculent material.

Another interesting and uncommon trait has been uncovered and described. Nakashima et al., (1996), have described a two-way sex change, known as bi-directional sex change, within two Gobiodon species, G. micropus and G. oculolineatus. This led to the discovery that other Gobiodon also have this ability, and it is now believed that all Gobiodon species can change sex. In doing so, Gobiodon deviates from the size-advantage model (Ghiselin 1969) that states if an individual could significantly increase its chance of reproduction success after a certain size was reached, it would change to that sex. Instead, bi-directional protogynous hermaphrodites are the ultimate in sex-changing species, as it guarantees a heterosexual pair at any given time. In most cases, the smaller fish of the heterosexual pair is the female. The only time this is not true is when a small male is placed in the same coral head as a large female. It was found that in pairs which started as two females, the larger of the two became male. In pairs that started as two males, the smaller of the two changed to female (Munday et al. 1998).

In the Home Aquarium

Gobiodon sp. have a tough time adjusting to captive care, since it is all too often that these fish arrive at our local fish stores emaciated. This is most likely due to the stressful transit period, which results in the fish not eating. Being a smaller fish, and having what appears to be a fairly quick metabolism, not many of these fish make it to the hobbyist tank without having been starved to some degree or another. To compound this problem, they regularly require live foods and special attention until accustomed to aquarium life. Frozen/thawed foods can be offered first, but if they are not accepted, be prepared to offer live food. Upon arrival of a new goby, special care should be taken to ensure large quantities of food are offered to the new arrivals without fouling the aquarium water. Live brine shrimp is the most available type of live food. Try to "gut-load" these live Artemia with phytoplankton if the possibility exists. Once the goby has accepted live food, they may slowly be weaned off the live food until they eventually are accepting frozen/thawed or prepared foods. Any of the commercially available foods suitable for a carnivore should be sufficient. Be sure to provide a varied diet, and that the food is small enough to fit into their tiny mouths.

Unfortunately, most Gobiodon individuals arrive to the retailer looking similar to this one. Note the sunken stomach. If possible, try to avoid fish that are starved like this. Otherwise, be prepared to nurse them back to health. Photo courtesy of Sahin Chowdhury.

Tank mates for Gobiodon must be carefully chosen. Though these fish do have a toxic mucus on their skin for protection, it doesn't mean you can mix and match haphazardly. Fish that are aggressive feeders should be avoided as tankmates, at least until after the Gobiodon has been fattened up and is readily accustomed to the aquarium. A refugium can be helpful during the transition period, hopefully offering an abundance of their favorite natural foods, copepods. An established tank stocked heavily with Acropora spp. will assist in mixing these fish with more aggressive swimmers. The Gobiodon species will take refuge within the branches of these corals. The more threatening the tank mates, the deeper into the branches the Gobiodon will retreat. In a peaceful aquarium Gobiodon spp. will normally remain on the tips of the corals within full view of the hobbyist.

Compatibility chart for members of the genus Gobiodon:

Fish	Will Co-Exist	May Co-Exist	Will Not Co-Exist	Notes
Angels, Dwarf		X		Most dwarfs should ignore Gobiodon individuals.
Angels, Large		X		Aggressive swimmers and feeders.
Anthias	X			Excellent choice.
Assessors	X			Excellent choice.
Basses		X		Most adult Basses may harass Gobiodon species.
Batfish		X		Aggressive swimmers and feeders.
Blennies	X			Excellent choice.
Boxfishes		X		Overall size will keep the Gobiodon hiding.
Butterflies		X		Aggressive swimmers and feeders.
Cardinals	X			Excellent choice.
Catfish		X		May harass Gobiodon species.
Comet	X			Excellent choice.
Cowfish			X	Overall size will keep the Gobiodon in hiding.
Damsels		X		Most Damsels are too aggressive for Gobiodon species.
Dottybacks		X		May attack and kill Gobiodon species.
Dragonets	X			Excellent choice.
Drums	X			Excellent choice.
Eels		X		May harass Gobiodon species.
Filefish	X			Excellent choice.
Frogfish			X	May try to consume Gobiodon species.
Goatfish			X	Large adults may harass Gobiodon species.
Gobies	X			Excellent choice.
Grammas	X			Excellent choice.
Groupers			X	May attempt to consume Gobiodon species.
Hamlets	X			Excellent choice.
Hawkfish			X	Adults may harass Gobiodon species.
Jawfish	X			Excellent choice.
Lionfish			X	May attempt to consume Gobiodon species.
Parrotfish		X		Aggressive swimmers and feeders.
Pineapple Fish	X			Excellent choice.
Pipefish	X			Excellent choice.
Puffers			X	May attempt to consume Gobiodon species.
Rabbitfish		X		Aggressive swimmers and feeders.
Sand Perches		X		Adults can be aggressive.
Scorpionfish			X	May attempt to consume Gobiodon species.
Seahorses	X			Excellent choice.
Snappers			X	May attempt to consume Gobiodon species.
Soapfishes			X	May attempt to consume Gobiodon species.
Soldierfish			X	May attempt to consume Gobiodon species.
Spinecheeks		X		Adult size can be intimidating.
Squirrelfish			X	May attempt to consume Gobiodon species.
Surgeonfish		X		Aggressive swimmers and feeders.
Sweetlips		X		Adult size can be intimidating.
Tilefish	X			Excellent choice.
Toadfish			X	May attempt to consume Gobiodon species.
Triggerfish			X	May attempt to consume Gobiodon species.
Waspfish			X	May attempt to consume Gobiodon species.
Wrasses		X		Aggressive swimmers and feeders.

Note: While many of the fish listed are good tank mates for members of the genus Gobiodon, you should research each fish individually before adding it to your aquarium. Some of the fish mentioned are better left in the ocean, or for advanced aquarists.

Although fish of the genus Gobiodon are obligate coral dwellers, usually utilizing the genus Acropora, it is not absolutely necessary that Acropora be present in their tank. In the home aquarium Gobiodon sp. will often co-exist with other stony corals, or even soft corals, lacking more preferable options. In all instances, if their preferred coral is available, it will be utilized. In aquariums without sufficient coral growth, it is likely that the Gobiodon sp. will either hide within rockwork, or seek out any other hiding places it can find. Given this type of environment, it will not be comfortable, and most likely will not adapt well to captivity. Due to their obligate coral dwelling nature, they can easily be kept in small or nano reef aquariums.

Captive Reproduction

Although captive spawning is a regular occurrence in Gobiodon species, raising the small fry seems to be less than easy. Obtaining a pair is simply a matter of obtaining two of the same species, since they will change sex to become a mated pair. Once mated, the female will attach circular bands of eggs around the branches of their preferred coral. The male immediately fertilizes and guards the eggs. The egg mass, that can contain up to 1000 eggs, hatches on the evening of the fourth or fifth day. Rotifers should be the first food offered to fry, with a possible transition to newly hatched Artemia nauplii around day 25. Around day 33, the fry go through a metamorphosis, settle, and begin to perch on the sides of the aquarium's glass. Their first coloration has been noted to occur on day 40 (Breeder's Registry).

Some awesome photos of Gobiodon histrio spawning above and a Gobiodon acicularis below. Note how they have cleared away live tissue from the base of the coral and then wrapped the eggs around the branches. Photos courtesy of Chuck Fiterman. Graphics by Skip Attix.

Meet the Species

Two species of Gobiodon are regularly regarded as being the most popular. The first is Gobiodon okinawae, or the yellow clown goby. Luckily for aquarists, this bright yellow fish is one of the most outgoing of Gobiodon. It will frequently perch on the glass of the aquarium, and regularly sits on the tips of the corals, rather than deep inside the colony. Gobiodon okinawae can be found on the largest variety of acroporid corals (Myers, 1991).

The bright yellow coloration associated with Gobiodon okinawae is quick to grab the attention of most hobbyists. Photos courtesy of Chuck Fiterman.

The other favorite Gobiodon among hobbyists is the Green Clown Goby, or Gobiodon histrio. One look at the clown-like paintwork on the face and body is usually enough for the aquarist to fall in love. Two color varieties, possibly separate species, exist for G. histrio. The first variety of G. histrio has a black spot on the upper margin of the operculum. The pectoral fins are generally pale green to light brown. The second coloration pattern has not yet been definitively published, largely due to inadequate analysis, but is commonly referred to as G. histrio "erythropilus." The coloration of this variation is nearly identical to G. histrio, except the black spot on the operculum is missing and the pectoral fins are generally yellowish with a fine black margin (Suzuki et al., 1995). In the wild both species colonize Acropora nasuta most frequently, but can also be found on A. valida, A. millepora, and sometimes A. tenuis. It is rare to find more than a single pair of G. histrio per coral colony (Patton, 1994)

Gobiodon histrio is camouflaged rather well inside this Nepthea sp. Photo courtesy of Ryan Baker.

Although a large percentage of the clown gobies available in the trade will be one of the two previously mentioned species, a couple more show up less frequently. Gobiodon citrinus, or the Citron goby, is the largest of clown gobies, measuring up to 60 mm. Four light blue bands are located on the head as well as single blue lines along the base of the dorsal and anal fins. A single black spot is located on the operculum. Overall, the fish have a yellow to brownish yellow coloration. They are most likely to be found residing within the branches of A. nobilis (Kailola, 1991, Munro, 1967, Randall et al., 1990).

 

Clown gobies will associate with most any soft or hard corals when in the home reef aquarium. Here we see Gobiodon citrinus relaxing in a Lobophytum sp. Photo by Henry Schultz.

Another photo of the largest of clown gobies, Gobiodon citrinus, this time relaxing in a bed of frilly mushrooms. Photo courtesy of Carlos Chacon.

The Black clown goby, or Gobiodon ceramensis, is an intriguing Gobiodon due to its intense black coloration. The entire fish is midnight black. Unlike its congeners, G. ceramensis is most likely found on corals from the family Pocilloporidae, most notably Stylophora pistillata (Tyler, 1971). Don't confuse G. ceramensis with its nearly identical cousin, Gobiodon acicularis. Only one physical difference exists between the two; G. acicularis has an extra long first dorsal spine. However, G. acicularis can also be found on different corals than G. ceramensis. G. acicularis can only be found on Echinopora horrida, E. mammiformis and Hydnophora rigida (Munday et al. 1999).

As is clearly evident in these two photos of Gobiodon acicularis, its intense black coloration can stand out rather well against some brightly colored SPS. Photos by Chuck Fiterman.

Gobiodon rivulatus has occasionally shown up in the trade in recent times. This fish lacks a common name, though it is usually sold under the common name of "Citron Goby." Gobiodon rivulatus is similar in appearance to G. citrinus, but is missing the blue lines on the base of the dorsal and anal fins. The blue lines it does have are narrow and wavy, and extend down the body of the fish rather than just appearing on the head as with G. citrinus. The overall color of these fish are highly variable, from a dark brown to light brown (Winterbottom & Emery, 1996). This species is most frequently found associated with Acropora gemmifera and A. secale, but will inhabit a large variety of acroporid species (Munday et al., 1997).

This photo of Gobiodon rivulatus was taken shortly after collection for research. Without special precautions, the clown gobies collected for research will lose their coloration quickly. Photo courtesy of Rick Winterbottom and the Royal Ontario Museum.

Up until 1999, Gobiodon brochus was known as Gobiodon micropus. It was then that Harold and Winterbottom (1999) discovered the protruding lip containing tiny teeth, which set it apart from G. micropus. Also, G. brochus has 10 - 12 dorsal fin rays and 9 - 10 branched anal fin rays, whereas G. micropus has 12 - 13 dorsal fin rays and 11 anal fin rays.

Though not entirely obvious, with close observation, you should be able to note the "tooth pad" on Gobiodon brochus in this photo. This fish has been nicknamed "velcro lips" by Rick Winterbottom and Anthony Harold, and chances are good "velcro lips" could end up being the "common name" of this fish in our hobby. Photo courtesy of Rick Winterbottom and the Royal Ontario Museum.

In Conclusion

Gobiodon gobies make adorable additions to the reef aquarium. If the hobbyist has an aquarium with suitable coral growth, and is willing to take on the challenge of fattening one up upon purchase, these gobies can fare extremely well in captivity. Never before would you have believed you could find so much personality in a fish that barely moves!

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