Glassfish

Photo: Jean-Paul Cassez · CC BY-NC

A collective term used for several species of small, transparent schooling fish — most commonly cardinalfish or sweepers — whose schools form shimmering, shifting clouds in reef crevices and beneath overhangs. Their near-transparency is achieved through reduced pigmentation and a reflective layer along the lateral line. Glassfish schools are primary food for predators like batfish, lionfish, and groupers. For photographers, the interaction between a glassfish school and a predator swimming through it is one of the classic reef behaviour shots.