By day, these brilliantly colored fish gather in small groups just above the edges of steep reef slopes where strong currents provide a steady supply of the tiny, drifting animal plankton on which they feed. By night, or when larger predators threaten, they seek shelter among the nooks and crannies of the reef.
Only males sport the bright, square spots on their sides that give this fish its common name. Squarespots are most common at depths of around 100 feet (30 m) or more. There in the dim light, their spots seem to glow, warning rival males and catching the eye of females.
In places, unscrupulous collectors use cyanide, bleach and other chemicals to catch reef fishes for the pet trade. These poisons can kill fishes, corals and other reef life. Fishermen in the South Pacific and Southeast Asia often dynamite reefs to kill fishes for food. The blast stuns the fishes, which then float to the surface where they can be easily scooped up. But the explosions destroy the reefs and kill many more animals than just those taken for food.
In addition to the bright spots on their sides, males perform acrobatic swimming displays to mark their territories and attract mates.
All squarespots start life as females. As they grow, some change into males.