Four centimeters (1.6 in) of stout black fish with a bright orange-red head covered in short fleshy papillae. It lives wedged among the branches of a Stylophora or Pocillopora colony and effectively never leaves it, so the way to find one is to stop looking at the reef and start looking into a single coral head.
The coral gets something back. When a colony is touched by the toxic green alga Chlorodesmis, it releases a chemical signal, and these gobies respond by chewing the alga back - the fish that live in a coral head measurably reduce the damage the alga does. It is one of the cleanest demonstrations that a coral can call for help and be answered.
Protection runs both ways. The fish is a poor swimmer with no chance in open water, so it lives permanently inside a stinging colony that few predators will reach into, and it coats itself in a bitter skin mucus that discourages the ones that would. Its sex is negotiable: a pair forms from whichever two fish arrive, and one becomes male.
- tiny stout fish, black body with a bright orange-red head
- head covered in short fleshy papillae, giving a velvety look
- wedged between the branches of a small stony coral
- length up to 4 cm
