SquirrelfishesHolocentrinae

A squirrelfish spends the entire day in plain sight and gets away with it.

Almost every small reef fish solves daylight by disappearing into something. These sit at the mouth of a cave or under an overhang, facing out, in a loose row, with nothing between them and the open water. What they have instead of cover is armor. The scales carry toothed rear edges rough enough to catch on skin, the gill cover is finished with spines at the back corner, the first dorsal is a row of stiff points that locks upright, and there are more spines in the anal and pelvic fins. A predator that swallows one is committing to a mouthful of hooks, and in one genus the cheek spine is venomous as well, which the species pages take up. The result is a fish that does not need to run and mostly does not bother.

The eye is the other half of the design and it is a night instrument. It takes up a third of the head, it is packed for gathering light rather than for detail, and behind the retina is a reflective layer of the kind that makes a cat's eyes shine, so light that missed a cell on the way in gets a second chance on the way out. That is why a torch under a ledge comes back at you as a row of points before you can make out a single fish. Why the fish should be red in a place where there is no red light is on the species pages.

Underwater the useful skill is telling the two halves of the group apart, and it is not the color. Soldierfishes have a blunt rounded snout, an enormous eye, plain red flanks and usually a dark bar down the rear edge of the gill opening, and they hover in open water under the overhang in loose company. Squirrelfishes proper have a pointed snout, white or silver stripes running the length of a red body, and a long spine at the cheek, and they hold lower and closer to the rock. Which one you are looking at also tells you what it will eat after dark, and the species pages have that.

Twelve are listed here, and by day they are the most reliable fish on the reef: the same crack, the same animals, week after week. The interesting hours are the ones divers are not in the water for, when the whole row leaves the ledge and spreads out over reef and sand.