GlassfishesAmbassidae

Glassfishes are small, deep-bodied fishes whose flesh is transparent enough to show the spine and the silvery sac of the gut straight through the side. A shoal of them in a cave mouth reads as a shimmer rather than as fish, which is exactly the point: transparency is camouflage in open water where there is nothing to hide behind.

They gather in dense, slow-moving schools in shade - under jetties, inside wrecks, in the roof of a cave - and spill out at dusk to feed on zooplankton. Most species prefer the edge where the sea meets fresh water, so estuaries, mangroves and lagoons hold more of them than open reef does.

The family is far better known to aquarists than to divers, and not happily: the so-called painted glassfish sold in shops is a glassfish injected with dye, a practice that kills most of the fish it is done to. The wild animal has no colour to paint.