Blue-Spotted Dragonet

A dragonet has no scales anywhere on it. What covers the fish instead is bare skin under a heavy coat of mucus, and in this family that mucus is bitter and carries compounds that make the animal unpleasant to swallow. A predator that takes one usually spits it out again.

The second family trait is a weapon you have to look for. On the rear edge of the gill cover sits a stout spine, barbed along its length, and every dragonet in the world has one. The number and direction of its hooks differ from species to species, which is why every identification key for the group opens with it.

This one sits in Diplogrammus, a small genus separated from the ordinary dragonets by a loose fold of skin that runs along the lower side of the body from behind the head almost to the tail. On the head, look for blue lines radiating down and out from below the eye. Males are golden above with silver mottling, dark speckles and a row of dark blue spots along the flank, and carry a black area at the back of the tall first dorsal fin. Females are plain buff.

It lives on shallow sand, in weed and in tide pools, from just under the surface to about 20 m, and it barely swims. It walks, propped on thick pelvic fins, shuffling over the bottom and picking small crustaceans and worms out of the sediment.

That bottom is the entire world of this fish except for a few seconds at a time. A pair courts toward dusk, the male raising his first dorsal fin at the female like a flag, and then the two rise together off the sand, release eggs and milt at the top of the climb, and drop straight back down. The short vertical trip is the only time the fish leaves the sea floor.