Loki Whipgoby

To breed, this goby damages the animal it lives on. It bites the living polyps off a short length of its sea whip, leaves a bare strip of skeleton, and sticks the egg clutch to it. The male then sits over the eggs and fans them until they hatch. Gobies of this genus do it on wire corals, sea whips and gorgonians alike, and the cleared patch stays visible on the host afterward.

Everything else about the fish follows from living on a branch no thicker than a pencil lead. The pelvic fins are joined underneath into a disc that grips the coral, so the goby can hold station in current without swimming. It shuffles around the branch rather than off it, keeping the whip between itself and whatever is approaching, which is why the photograph you get is usually of the far side of a sea whip.

At a maximum of about 4.5 centimeters, and commonly nearer 3, it is close to invisible. The body is translucent, crossed by narrow red bars that broaden into a dusky golden tone below, with brown saddles along the back and a brown blotch at the base of the tail. A pale line runs the length of the spine. Against a whip of the same color, none of that reads until you are half a meter away.

It turns up between about 6 and 45 meters, wherever sea whips and gorgonians grow on slopes and walls with some water movement. In this sea it has been photographed at Sharm El Naga and recorded from 🇸🇩 Sudan, the Sinai coast and the 🌊 Gulf of Aden, and the same species runs east across the Indo-Pacific to Hawaii.

The practical advice is to stop searching the water and start searching the coral. Pick a whip, follow it from the base up, and look for a dark blotch that moves.