Sea chubKyphosidae

Sea chubs live where the water hits. Along the reef crest, in the surge line where swell breaks and the water is going in two directions at once, there is often a group of plain gray fish holding position as though none of that were happening, and it is almost always these. Most reef fish keep out of that zone. The chub works it because the weed grows fastest there, and the animal is built for it: a deep muscular oval, a small mouth for cropping, and a stiff tail that holds a line in moving water.

The old name for the family is rudderfish, and it comes from the habit of following ships. A chub will attach itself to anything that floats and go with it, and the young of the family live far offshore inside drifting rafts of weed, feeding in the raft and hiding in it. That is how a fish of rocky coasts and reef crests ends up with a range that crosses oceans.

Telling one from another is a job for an expert, and for a long time it defeated the experts too. The three species in this sea are all the same silver-gray oval with faint bronze lines along the flank, separated on fin ray counts, tooth shape and small differences in the head, and the genus carried a long list of names that turned out to be a much smaller number of real fish, sorted out only when counts and genetics were put together. If you photograph one, photograph the fins.

Nothing about a chub is decorative, which is worth a minute of attention on a reef where everything else is competing for it. This is a generalist herbivore that can hold station in the surf, cross an ocean under a floating log and turn coarse seaweed into fish, and it is doing all of that in plain sight while divers swim past it toward the coral.