Off the coast of Brazil, a scuba diver captured something remarkable on video: a wrasse fish gripped a mollusk in its mouth, darted toward a rock, and began pounding the shell until it cracked open. This fish was using tools to access food.
In a new study, researchers led by Juliette Tariel-Adam of Macquarie University document the first video-confirmed cases of tool use in five species of New World Halichoeres wrasses. These rainbow-colored reef dwellers, found across the Caribbean and Western Atlantic, use natural “anvils”—rocks, coral heads, even discarded shells—to break open hard-shelled prey. It’s a startling glimpse into a type of intelligence we’re only beginning to understand.
A fish with a plan
Wrasses are vibrant, agile reef-dwellers found in tropical and subtropical waters. In this study, scientists observed multiple individuals picking up hard-shelled prey and smashing them repeatedly against hard surfaces. The fish targeted specific rocks—called “anvils”—to help access their meals.
The new findings expand a growing list of underwater tool-users. Through a global citizen science initiative called Fish Tool Use, divers submitted footage from Brazil, the Caribbean, and beyond. The researchers confirmed 16 new observations of tool use across five Halichoeres species: H. brasiliensis, H. poeyi, H. radiatus, H. garnoti, and H. bivittatus (I’m glad I stuck to the Latin name on this one). Some preyed on sea urchins, others on mollusks or hermit crabs, each time cracking them open using the reef itself as a weapon.
Anvil use in fish typically involves three steps: grab, swim, and smash. These fish used a surprising range of anvil types—dead coral, rubble, rock platforms—and often switched between them mid-meal. And it wasn’t just clumsy thrashing. Video analysis showed that wrasses sometimes changed angles and striking points, revealing a high degree of spatial awareness.
This isn’t the first time wrasses have surprised scientists. A 2024 study in Coral Reefs recorded similar behavior in Indian Ocean species, such as the checkerboard wrasse (Halichoeres hortulanus) and Jansen’s wrasse (Thalassoma jansenii). This new study significantly expands both the number of species known to use tools and the geographical range where this behavior occurs.
Ancient Roots or Modern Innovation?
Wrasses are one of the most diverse families of marine fish, with over 550 species in the family Labridae. Yet only 26 species have been documented using anvils. The newly recorded wrasses belong to a sub-clade of New World Halichoeres that likely diverged around 20 million years ago. The research team plotted these species on a detailed fish family tree and found a pattern suggesting that tool use might be ancestral—not a new innovation.
If true, that raises a tantalizing question: why don’t more fish use tools?
Some scientists argue that environmental factors play a role. In land animals, tool use often arises in habitats where food is hard to access without tools—think chimpanzees cracking nuts or otters using rocks to open shellfish. The same might be true underwater. Many of the wrasse sightings came from areas with fewer easy-to-eat prey.
Tool use might also require physical and neural adaptations. In birds and primates, the behavior is often linked to large brains, good vision, and dexterous limbs. In the wrasse’s case, a sharp beak-like mouth and a knack for repetition gets the job done.
Rethinking Tool Use — Again
The discovery may come as a surprise to those who still associate tool use with primates or birds. But in fact, the animal kingdom has been chipping away at that stereotype for years.
In 1960, Dr. Jane Goodall shocked the scientific world by documenting chimpanzees at Gombe stripping leaves from twigs to “fish” termites from their mounds. Her mentor, Dr. Louis Leakey, famously responded: “Now we must redefine tool, redefine Man, or accept chimpanzees as humans.”
That dramatic moment sparked a re-evaluation of animal intelligence. Since then, crows, sea otters, elephants, dolphins, and even octopuses have been found using tools. Capuchins use rocks to crack nuts. Orangutans have been seen using sticks as whistles, gloves, and even sex toys. Dolphins use sponges to protect their snouts while foraging on the seafloor. Bonobos and gorillas employ sticks to gauge water depth.
And now, wrasses.
Though the behaviors differ—from termite-fishing to nut-cracking—they share common threads: planning, manipulation of objects, and often, the innovation to solve a specific problem. The wrasses’ use of anvils fits neatly into that framework.
What This Means for Evolution
The implications of this research ripple far beyond coral reefs.
Tool use was once viewed as a pinnacle of cognitive evolution, something that set humans apart from the rest of the animal kingdom. But if wrasses—small-brained fish with no hands—can learn to use tools, it suggests that complex behaviors may arise under the right ecological pressures, regardless of lineage or brain size.
The study’s authors hope the findings will prompt more careful observation of marine life. Incidental sightings like those documented by divers could be key to uncovering more examples of tool use hidden in plain sight.
The findings were published in the journal Coral Reefs.
