Green Clown Goby (Gobiodon histrio)
Also known as the Broad-barred goby and Earspot Coral Goby. Reaches a massive size of 1 ½ inches. Lifespan in the wild 1-3 years in captivity have survived for 5 years.
Was first described by French zoologist Achille Valenciennes in 1837.
Characterized by mainly green body color with red to violet stripes or forming broken lines or row of spots on side; 4-5 reddish bars on head; absence of scales; complete pelvic fin frenum and basal membrane; depth of body at level of pelvic fin.
Native to the Indian Ocean from the Red sea to the western Pacific Ocean to southern Japan, Samoa and the Great Barrier Reef. G. histrio is a dwells solitary or in pairs among branches of Acropora corals , being found at depths of from 6 to 50 ft. Gobies are among the most habitat-specialized fishes on coral reefs, living among the branches of scleratinian corals (stony corals) and having specific associations with one or more species of coral, mostly from the genus Acropora. The Green Clown Goby was observed in corals belonging to a number of different Acropora species, but only A. nasuta was actively favored, i.e., used more frequently than expected based simply on its availability. On the Great Barrier Reef , where there are two color morphs of A. nasuta, Green Clown Gobies usually inhabit colonies of the "blue-tip" morph and only rarely the "brown-tip" morph, although these color forms seem truly to be members of the same species. Gobiodon histrio rarely leave the shelter of their host coral colony. However, oxygen levels in this environment can drop very low and at very low tide the entire coral can be exposed to the air. The high tolerance of Green Clown Gobies for hypoxia and their limited ability to obtain oxygen even when exposed to the air may be essential adaptations for their lifestyle.
On the IUCN Red List Gobiodon histrio is listed as Least Concern. This fish produces a toxin that deters predators. The only population pressures come from the aquarium trade. When disturbed, it releases compounds that inhibit the locomotion of other fish. At high enough concentrations, the toxin causes the predator to lose equilibrium and tip over. It takes part in a mutualistic relationship with a species of coral, Acropora nasuta. When the coral is damaged by toxic Chlorodesmis algae (Turtleweed), it produces a compound that attracts the fish. The fish eat the algae and this enhances their toxicity. The Green Clown Goby is diurnal and extremely active and peaceful. It will sift through the substrate in search of food and if there is not an established substrate it will need to be feed 3 times a day. Foods include live brine shrimp, frozen, freeze dried, and fresh cut carnivorous preparations, flake food, live black worms, and krill.
Captive breeding has been successful but there are no visible signs of sexual differences. G. histrio can change sex in either direction. When a pair of gobies of the same sex colonize a new coral patch, one of them changes to the opposite sex. If 2 males pair up the smaller will become a female, if 2 females pair up the larger becomes a male. G. Histrio is listed as reef safe but caution should be taken with Acropora, especially Acropora nasuta, the pair will sometimes tear the flesh to make a nest. So in a heavy Acropora tank they should only be kept singularly. Conversely if you do have a heavy Acropora tank you want one in it because they are a helper goby and will keep your corals clean of harmful algae and nuisance Acro “red bugs”.
There is no consistent listing on min. sized tank for G. Histrio have seen 5g to 30g.
It is unlisted when G. Histrio entered into the hobby. Nor are there any hybrids listed.