Longhorn Cowfish

With two long "horns" projecting forward from above its eyes and two spines pointing backward from the lower rear corners of its body, the longhorn cowfish is one of the strangest-looking marine fish. Its body is encased in a rigid box made of bony plates; only its fins, eyes and small mouth move. Its color varies between yellow, olive green and orange, covered in small blue spots. The tail fin grows noticeably longer with age.

Toxin warning: like all boxfish, it releases toxin from its skin into the water when stressed, sick or dying. In a small or crowded aquarium this toxin can kill the other fish and the cowfish itself. All individuals are wild-collected; the tiny juveniles sold do not cope well with shipping and starvation.

It lives in coastal waters of the Indo-Pacific, over muddy and sandy bottoms, in bays, harbors and estuaries; it occasionally enters brackish water. Juveniles are found in small groups near river mouths, while adults are solitary. It blows into the sand to expose the invertebrates beneath and eats them.

• Volume: at least 800 liters for an adult; a large sandy area and swimming space.
• Water: salinity 1.023–1.026 specific gravity, pH 8.1–8.4, temperature 24–27°C.
• Toxin precautions: use a powerful protein skimmer and continuous activated carbon; if the fish falls ill or dies, do a large water change immediately.
• Decor: avoid narrow passages where it could snag its horns and sharp decor.
• Reef compatibility: not reef safe. It eats invertebrates in the sand, small shrimp and tube worms and may pick at some corals; the toxin risk is also dangerous for invertebrates.

Omnivorous. Offer frozen mysis, brine shrimp, chopped mussel, shrimp and squid, and foods containing seaweed and spirulina. It is a slow eater; fast tankmates may snatch its food. Juveniles should be fed small amounts 3 times a day.

Peaceful, slow and curious; it can learn to take food from its keeper's hand. It hovers like a helicopter as it swims and jets water into the sand with its mouth. Aggressive or fin-nipping fish stress it and can cause it to release toxin.

Good companions: peaceful medium-sized fish in a large, calm aquarium: cardinalfish, calm tangs, foxface, Heniochus, Genicanthus angelfish.

Avoid: triggerfish, aggressive wrasses and damsels, fin-nipping species; a second boxfish; reef aquariums and small aquariums.

Keep a single individual in the aquarium.

In the wild it releases pelagic eggs. It does not breed in home aquariums.

• Poisoning event: toxin release in the shipping bag or in a stressful environment is the biggest risk; do not pour the water from the bag into the aquarium.
• Starvation: tiny juveniles quickly waste away if not fed often.
• Marine ich: it is prone to the disease but sensitive to copper treatment.

The sexes cannot be reliably told apart externally.