Two of these fish live inside one coral, and neither of them can safely go looking for anything better. Coral gobies are poor swimmers in the open and everything on the reef eats a fish this size, so a move between colonies is a gamble that often does not pay.
The genus deals with that by making sex negotiable in both directions. If two males end up in the same coral, one becomes female. If two females do, one becomes male. Either change can happen, and it can happen again later, so any two adults that find themselves in the same colony can form a breeding pair without anyone having to travel.
The other adaptation is chemical. The skin secretes a bitter toxic mucus, which is where the name poison goby comes from: predators that take one spit it out, and the fish keeps a coating of the stuff on it at all times. It is also thick enough to be a nuisance in aquariums, where a stressed coral goby can foul the water.
They can even breathe air for short periods, which matters on a reef flat when a low tide leaves the coral head half dry.
The genus. Gobiodon Bleeker 1856 - odon (tooth). ETYFish
- stubby scaleless body, pale yellow through to dark brown
- blue vertical lines around the eye and across the gill cover
- blue stripe along the base of the dorsal fin
- wedged among the branches of a single Acropora colony
- up to 6.6 cm
