🐡 Trunkfish in Punta Cana: The Reef's Armored Boxfish

Some reef fish dart, some hover, and then there is the trunkfish, which putters along like a small armored box with fins attached. Its body is sealed inside a rigid shell of fused bony plates, so only the fins, eyes, mouth and tail can move. It looks clumsy, but it is a precise little machine: it can turn on the spot, hold position in surge, and back out of a crevice the way it came in.

Four members of this family (the boxfishes, Ostraciidae) live on Caribbean reefs: two trunkfishes and two cowfishes. On a typical dive in Punta Cana you have a good chance of meeting at least one of them, and once you know the field marks they are some of the easiest fish on the reef to name. They also carry a chemical secret that every diver and aquarium keeper should know about.

Quick Facts

• Species: smooth trunkfish, Lactophrys triqueter; spotted trunkfish, Lactophrys bicaudalis; honeycomb cowfish, Acanthostracion polygonium; scrawled cowfish, Acanthostracion quadricornis
• Names: the two trunkfishes are sometimes filed under Rhinesomus, and the cowfishes used to be placed in Lactophrys; the World Register of Marine Species currently accepts the names above
• Size: usually about 20–25 cm (8–10 in); FishBase gives maximums of roughly 47–55 cm depending on the species
• Diet: small bottom invertebrates such as worms, crustaceans, mollusks and tunicates, plus sponges and seagrass; the spotted trunkfish also takes urchins and sea cucumbers
• Depth: from about 1–3 m down to 50 m for the trunkfishes and 80 m for the cowfishes, most often on shallow reefs
• Range: tropical western Atlantic, including the whole Caribbean, Florida, the Gulf of Mexico and south to Brazil
• Status: all four are listed as Least Concern by the IUCN

How to Recognize Trunkfish and Cowfish

All four share the boxy, triangular body, a small puckered mouth and big, mobile eyes. The quickest split is the forehead: cowfishes have two short horns above the eyes, trunkfishes do not.

• Smooth trunkfish: dark body covered in small white spots, with a pale honeycomb pattern in the middle of the sides. No spines anywhere on the shell, which is where the name comes from. This is the one you will see most often.
• Spotted trunkfish: the reverse color scheme, a pale or whitish body with black spots, and white around the mouth. It has a pair of sharp spines on the lower rear of the shell, just in front of the anal fin. It tends to stay closer to ledges and holes.
• Honeycomb cowfish: horns, plus a bold pattern of pale hexagons outlined in darker lines, with a ring inside each cell. Its color can shift from pale to dark, so the base shade is not a reliable clue; the hexagons are.
• Scrawled cowfish: horns, but instead of hexagons it has irregular blue or bluish lines and spots scribbled across an olive or tan body. It prefers seagrass and sand edges more than the reef itself.

Juvenile smooth trunkfish are tiny, dark and covered in large yellowish spots, and divers often mistake them for a different animal entirely. If you see a pea-sized dark ball with spots wobbling over the bottom, that is probably what it is.

Behavior: Armor, Water Jets and a Toxin

With a rigid body, a trunkfish cannot flex its spine to swim. Instead it sculls with its dorsal and anal fins and steers with its pectorals, keeping the tail folded for short bursts of speed. That is why they look so deliberate, and why they can hover in one spot to feed.

Their best-known feeding trick is the water jet. A smooth trunkfish tilts head-down over the sand and blows a stream of water from its mouth, blasting away the top layer to uncover buried worms and crustaceans, which it then picks out. Watch for small clouds of sand puffing up beside a trunkfish: it is not digging, it is blowing.

The armor is only half of their defense. When stressed, boxfishes release a toxin called ostracitoxin (also known as pahutoxin) in the mucus on their skin. It is harmful to other fish and dissolves into the water, which is why stressed trunkfish have wiped out entire home aquariums. On an open reef the ocean dilutes it, and it poses no risk to a diver who simply watches. The lesson is the same one we teach for every animal: do not chase, corner or handle them.

Like other boxfishes, they spawn in open water, and their eggs and larvae drift with the plankton before settling on the reef.

Where to See Trunkfish in Punta Cana

The smooth trunkfish is a regular on our shallow reefs. On beginner sites like El Niño and the Finger Coral Plantation, both around 6 m (20 ft), we often find one working the sand patches between coral heads. At Park Reef, at 12 m (40 ft), they share the reef with turtles and squid. Spotted trunkfish are less common and more secretive, so check under ledges and around holes. The two cowfishes are occasional sightings, the honeycomb more often over reef and rubble, the scrawled near seagrass and sandy edges.

You will find the trunkfish on our species guide, next to its spiny cousin the porcupine fish. Both are slow swimmers and they rely on defense rather than speed.

Tips for Divers and Snorkelers

• Stay low and still a short distance away. A trunkfish that does not feel followed will go back to feeding, which is when you see the water jets.
• Never touch, herd or try to make one turn around for a photo. Stress is exactly what triggers the toxin.
• Keep your fins well off the bottom. These fish feed in the sand, and a cloud of silt ends the encounter for everyone.
• For photos, a head-on shot shows off the lips and eyes; a side shot shows the pattern you need for identification.
• Snorkelers can see smooth trunkfish over shallow sand and seagrass on calm days, since they often feed in just a few meters of water.

Frequently Asked Questions

Are trunkfish poisonous to touch?

The toxin is in the skin mucus and is released when the fish is stressed. It mainly harms other fish in enclosed water. You should not handle them anyway, for their sake as much as yours.

What is the difference between a trunkfish and a cowfish?

Both belong to the boxfish family. Cowfishes have two horn-like spines above the eyes; trunkfishes have none. Pattern then tells you the species.

How big do trunkfish get?

Most of the ones we see are about 20–25 cm (8–10 in). FishBase records maximums of around 47–48 cm for the trunkfishes and up to 55 cm for the scrawled cowfish.

Can you eat trunkfish?

They are eaten in parts of the Caribbean, where they are often called chapín. We would much rather see them on the reef, and they are far more interesting alive.

Want to watch a trunkfish blow its way through the sand? Join us for a two-tank reef dive in Punta Cana and our guides will help you spot all four boxfishes.