Yellow boxfish

The yellow boxfish is a marine fish in the family Ostraciidae, found across the Indo-Pacific on reefs and in lagoons. Juveniles are famously cube-shaped and bright yellow with black spots, becoming more elongated and dull yellowish-brown as they mature. The body is encased in a rigid bony carapace of fused plates. When stressed, it can release a toxin called ostracitoxin into the water, which is dangerous to other fish in a closed system. It is a slow, deliberate swimmer needing a peaceful marine aquarium with calm tankmates that will not outcompete it for food. It grazes on algae, small invertebrates, and sessile organisms, requiring a varied diet including vegetable matter. Because of its toxin release, sensitivity to water quality, and specialized care, it is recommended only for experienced marine aquarists.