TankBud

Longhorn cowfish

Lactoria cornuta

Also known as Horned Boxfish, Cow Trunkfish, Longhorn Boxfish

SaltwaterFish

Longhorn cowfish (Lactoria cornuta)
Diego Delso · CC BY-SA 4.0

Care at a glance

Temperature
75–81°F
24–27°C
pH
8.1–8.4
Adult size
18.1 in
46 cm
Minimum tank
250 gal
946 L
Temperament
Peaceful
Social behavior
Solitary
Tankmates
With caution
Swim level
Bottom
Diet
Omnivore
Difficulty
Difficult
Breeding
Hard
Rarity
Common
Reef safe
Not reef safe
Family
Ostraciidae
Origin
Indo-Pacific reefs, from the Red Sea and East Africa to the Marquesas, north to southern Japan

Overview

The longhorn cowfish is a slow, peaceful boxfish for a large, established saltwater tank. It is strictly for experienced keepers.

Did you know

The longhorn cowfish's rigid shell forces an unusual swimming style called ostraciiform locomotion. Its body stays essentially motionless while rapid beats of the dorsal, anal and pectoral fins scull it through the water. It trades speed for a precise, hovering control few reef fish can match, and saves the tail fin for quick bursts.

Caring for the longhorn cowfish

A longhorn cowfish needs a large, mature tank of at least 250 gal (946 L). Give it soft sand for its sand-blowing foraging habit and open water it can cruise without bumping into decor. It is not reef safe, since it picks at coral polyps, tubeworms and small invertebrates. Its toxin risk also rules out any tank that cannot be fully evacuated in an emergency.

Keep the water at 75 to 81°F (24 to 27°C) and a pH of 8.1 to 8.4. The cowfish is a slow, deliberate eater with a small mouth. Offer small meals of chopped clam, shrimp, mysis and marine algae several times a day.

Faster tank mates easily outcompete it for food, so introduce it before more assertive fish. Feed it somewhere it can find food at its own pace. Keep only one per tank, since it will not tolerate another longhorn cowfish.

Treat the longhorn cowfish 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. Breeding it is hard.

Good to know

The longhorn cowfish is a boxfish in the family Ostraciidae. Its box-shaped carapace of fused bony plates leaves almost no room for the body to flex. The long, permanent horns above its eyes, plus a shorter pair near the tail, are fixed bony spines. They are not the erectile spines of a porcupinefish and do not inflate or retract, but they make the fish harder to swallow. Like other boxfish, it can release a skin toxin called ostracitoxin (pahutoxin) into the water when badly stressed or dying. The toxin can poison every other fish in a closed aquarium system.

In the wild

The longhorn cowfish is native to Indo-Pacific reefs, from the Red Sea and East Africa to the Marquesas Islands. Its range runs north to southern Japan. It lives 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.

Common questions

What size tank does a longhorn cowfish need?

A longhorn cowfish needs at least 250 gal (946 L). It spends most of its time in the bottom.

What temperature and pH does a longhorn cowfish need?

A longhorn cowfish is comfortable at 75–81°F (24–27°C) with a pH of 8.1–8.4.

What does a longhorn cowfish eat?

A longhorn cowfish eats small meals of chopped clam, shrimp, mysis and marine algae, offered several times a day. It is a slow, deliberate eater with a small mouth.

How big does a longhorn cowfish get?

An adult longhorn cowfish reaches about 18.1 in (46 cm).

Related species