Longhorn cowfish

Care at a glance

Overview

Peaceful and slow, easily outcompeted for food by faster tankmates, so it does best introduced to the tank before more assertive fish and fed somewhere it can find food at its own pace. It is not reef safe: it picks at coral polyps, tubeworms, and small invertebrates, and its toxin risk rules out a tank that can't be fully evacuated in an emergency anyway. Offer small meals several times a day of chopped clam, shrimp, mysis, and marine algae, since it is a slow, deliberate eater with a small mouth. Keep only one per tank, since it won't tolerate another longhorn cowfish, and treat this as an expert-only fish for a large, established system: sudden stress, illness, or a rough net can trigger the toxin release that has wiped out entire tanks.

In the wild

Native to Indo-Pacific reefs from the Red Sea and East Africa to the Marquesas Islands, north to southern Japan, in lagoons, reef flats, estuaries, and sheltered bays down to about 45 m. Juveniles shelter around branching Acropora coral, while adults range more widely over sand, rubble, and weedy areas near reefs. It needs a large, mature tank of at least 946 litres (250 US gal), with soft sand for its sand-blowing foraging habit and open water it can cruise without bumping into decor.

Good to know

Its rigid, box-shaped carapace of fused bony plates leaves almost no room for the body to flex, so instead of swimming like a typical fish it sculls through the water using only its dorsal, anal, and pectoral fins, saving the tail fin for quick bursts of speed. The pair of long, permanent horns above its eyes, plus a shorter pair near the tail, are fixed bony spines rather than the erectile spines of a porcupinefish, there to make the fish harder to swallow rather than to inflate or retract. Like other boxfish, it can release a skin toxin called ostracitoxin (pahutoxin) into the water when badly stressed or dying, capable of poisoning every other fish in a closed aquarium system.

Common questions

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