A silver fish with an eye that takes up half its head, in a school that hangs in mid-water like a suspended cloud and turns as one animal. Up to 70 cm (28 in) in theory, around 25 in practice.
The eye is the whole design. This is a night feeder in a family of daytime hunters: after dark the schools break up and spread into open water to pick copepods and larvae out of the dark, one at a time, which needs light-gathering rather than speed. By day the fish reassemble and do nothing, which is when divers see them.
That is also why the schools are so tight. A fish that is not feeding has nothing to gain from spreading out and everything to gain from being one shape among thousands. Watch a jack make a pass and the school opens around it and closes behind, without a single fish leaving.
It is one of the most important small food fishes in the tropics, caught by the ton at night with lights - which works precisely because the eye that finds plankton in the dark also finds a lamp.
The species. Selar crumenophthalmus (Bloch 1793) - crumena (leather money bag or purse) + ophthalmos (eye). ETYFish
- slender silver fish with an eye far too large for its head
- dark spot on the edge of the gill cover
- scutes forming a keel along the rear half of the lateral line
- in tight schools that turn as one and hang almost motionless by day
- length up to 70 cm, most fish around 25 cm
