Longhorn cowfish knocks

The Longhorn Cowfish is one of the strangest looking reef fish in the Indo-Pacific. Its unique swimming technique makes the fish look like it is hovering.

All in the Name

Its scientific name is Lactoria cornuta. Lactoria means “milkcow” and cornutus means “horned.” The long horns on the head give this fish its common and scientific names. Another pair of shorter horns points backward near the tail. Combined with its box-like body, the fish looks almost unreal.

Longhorn Cowfish are found across the tropical Indo-Pacific. They live on coral reefs, sandy slopes, lagoons, and sheltered bays. Juveniles are often seen in shallow protected areas. Adults are usually solitary and move slowly over the reef while searching for food along the ocean floor. It can grow to a maximum length of 50 centimeters.

Fused bony plates cover its body like armor. This armor protects the fish from predators. The horns also make it difficult for larger fish to swallow them. A broken horn will grow back over time.

The color can vary from bright yellow to olive or tan. Many individuals have white or blue spots across the body. Juveniles are often brighter than adults. Some large adults become darker and the long head horns may appear shorter with age.

A Fish that Hovers

Despite the rigid body, the fish is surprisingly graceful underwater. It moves by fluttering its small fins while the body stays almost motionless. Scientists call this style of swimming ostraciiform. So, the Longhorn Cowfish appears to hover. Notice in our video how the fish moves its dorsal, anal, and pectoral fins to remain motionless in midwater.

It often hovers slowly over sand while blowing jets of water through its mouth when searching for food. The fish searches for worms, tiny crustaceans, and other hidden prey.

Sounds of the Longhorn Cowfish

The Longhorn Cowfish makes distinctive sounds underwater. It contracts special muscles connected to its swim bladder to make noises. When disturbed or handled, the fish can make knocking, clicking, grunting, or humming noises. Scientists discovered that the fish produces at least two different sound types. One is a short click with stronger volume. The other is a softer humming sound that can continue for long periods.

The knocking sound is surprisingly loud underwater. In our video, listen for the knocking sounds when the photographer approaches. The sound can resemble someone tapping lightly on wood or knocking inside a hollow container. Research suggests the fish can hear these low-frequency sounds produced by other cowfish.

Like many boxfish, the Longhorn Cowfish also has a dangerous defense mechanism. When severely stressed, it can release a toxic substance called ostracitoxin from its skin. This toxin can kill nearby fish in confined water such as aquariums.

Although awkward looking at first glance, the Longhorn Cowfish is a favorite subject for underwater photographers and divers. Its unusual shape, shy personality, and slow hovering movement make it unforgettable. Hearing the sharp knocking sounds underwater only adds to the experience.

For your chance to see and hear a Longhorn cowfish in Gorontalo, please contact us for your dive trip booking.