Yellow Boxfish

• When stressed it releases ostracitoxin through its skin, a poison capable of killing every fish in a closed aquarium, itself included.
• Its box shape, seemingly clumsy, generates vortices that stabilise the fish passively, and that hydrodynamic principle inspired the design of a Mercedes-Benz concept car in 2005.
• Adults lose the bright yellow of the juveniles and turn brown or bluish.
• Its body is encased in a box-shaped carapace of fused bony plates. Only the mouth, eyes, fins and tail poke out through the gaps.
• That armour comes at a cost: it cannot bend its body to swim, so it propels itself with its fins alone and moves along slowly, almost floating.
• If stressed it secretes through its skin a toxin called ostracitoxin. In a closed aquarium it can kill every fish in the tank, itself included, which is why it is a problematic species in the aquarium hobby.
• It is a protogynous hermaphrodite and forms harems of two to four females per male.
• Juveniles are an intense yellow with black spots, and the colour dulls with age until it turns bluish brown.
• Its genome was sequenced in 2023 precisely to understand the genetic basis of its two defences: the carapace and the toxin.

Skeleton type

Vertebrate - internal bony skeleton (fish)

Habitat & environment

Coral reefs and rubble bottoms of the Indo-Pacific, from 1 to 45 m

Sources consulted: FishBase (Froese & Pauly, eds.); Lista Roja de la UICN; Wei et al. (2023), Frontiers in Marine Science