Red Sea Dwarf Sweeper

Found in dense schools, often sharing their space with other fish, and moray eels, in and around caves, under ledges, and overhangs, of coastal, and off-shore reefs.
They feed nocturnally on zooplankton.
Western Indian Ocean - Egypt

Sweepers school during the day, but at night they float high above the bottom to hunt for larger zooplankton.
Several species are triangular shaped.