Some clever fish use tools to crack open prey

For decades, tool use was seen as the hallmark of human evolution. Later, researchers began to notice this skill in chimpanzees, crows, and even sea otters. But one group remained conspicuously absent from this conversation – fish.

They were thought to be too simple, too instinct-driven, and too limited in cognitive ability. That belief no longer holds.

A new study has revealed something remarkable: several wrasse species have been observed using hard surfaces to break open prey.

These behaviors don’t just challenge assumptions – they expand the very definition of what it means to be intelligent.

Dr. Juliette Tariel-Adam, the study’s lead author from Macquarie University, has spent years watching these small but clever reef fish. Her team tracked and recorded behaviors that were previously dismissed or unnoticed.

“Tool use is typically associated with humans, but this behavior is proof that fish are far cleverer than they get credit for,” said Dr. Tariel-Adam.

Fish use tools to smash prey

Wrasses are colorful reef fish found in warm oceans across the world. In this study, several species were observed picking up crabs, mollusks, and brittle stars in their mouths and striking them against rocks or coral heads.

This behavior is known as “anvil use,” a form of tool use that allows the fish to access prey they otherwise couldn’t consume.

The wrasses showed clear intentionality. They didn’t just drop their prey. They positioned it, swung their bodies with force, and adjusted their angles between strikes. They seemed to know what they were doing. This wasn’t random behavior – it was targeted, practiced, and often successful.

The study documented 16 new observations across five species within the New World Halichoeres group. Three of those species had never been seen using tools before. Two others were suspected to use tools, but now video evidence confirms this.

Tool use across oceans

These discoveries were made possible by a community science initiative called Fish Tool Use.

Through social media outreach, emails, and public engagement, the research team gathered videos and reports from divers and marine enthusiasts.

The observations came from Brazil, Colombia, the Turks and Caicos Islands, and beyond.

All five species observed belong to a closely related group in the Labridae family, the second most species-rich group of marine fish.

The team believes this behavior may have evolved in a common ancestor and persisted across related species.

Alternatively, anvil use may have emerged multiple times independently – a question that future research may help to answer.

“With these newly discovered tool-using species, it becomes clear that many species of wrasses use tools that we previously didn’t know about,” said Dr. Tariel-Adam.

Flexibility of fish tool use

One surprise in the study was the absence of laterality. In primates and crows, tool use often involves a dominant hand or claw.

Wrasses, however, appeared to use both sides of their bodies equally. In video analyses, they struck with either side depending on their position in the water.

This flexibility might offer an advantage. While lateralized tool use can be efficient, it also limits an animal’s options when environment or position changes.

Wrasses, on the other hand, can exploit anvils in any orientation, giving them a broader range of usable surfaces.

In addition, wrasses used many different types of anvils. Rocks, coral heads, rubble, even a live conch shell – all served the same purpose. They did not show strict preferences. They adapted to what was around them.

This suggests not only cognitive flexibility but a level of environmental awareness as well.

Food and competition on the reef

Using tools to break open hard prey is not without its costs. The action requires energy, especially when it involves several powerful strikes.

Videos show the fish sometimes lose their grip or need to readjust by spitting out and re-securing their prey. Despite this, the behavior is consistently successful.

Sometimes, other fish circle the scene. In 12 of 19 observations, nearby fish either attempted to steal food or got chased away. In one case, a juvenile wrasse stole a brittle star from an adult just after it had broken off a piece. Tool use brings not only food, but attention – and not always the good kind.

Still, the benefits seem to outweigh the risks. Access to shelled prey means more food options and better nutrition.

For smaller wrasses, who might not have the jaw strength to crack shells without help, this strategy opens a new dietary path. It allows them to eat prey that would otherwise be unavailable to them.

Evolutionary puzzle of tool use

The study’s results open a new chapter in animal cognition. Fish now join a growing list of tool-using animals that includes primates, parrots, octopuses, wasps, and crabs. But why have only some species developed this behavior?

Tool use is likely influenced by ecological pressures – scarce food, competition, or environmental structure. In the case of wrasses, their diverse habitats, sharp learning skills, and wide range of prey may all play a role. Yet, the exact reasons remain unclear.

Professor Culum Brown, senior author of the study and head of Macquarie University’s Fish Lab, believes this behavior sheds light on the broader story of intelligence in the animal world.

“They demonstrate flexible and dexterous tool use, expanding our understanding of tool use evolution in the animal kingdom,” noted Professor Brown.

What happens next

The researchers want to see more. Most documented tool use events are still opportunistic. Controlled studies – where prey is offered in experimental settings – could bring new insights.

The team hopes to receive more submissions from the public, helping them fill the gaps in geography and species data.

Those interested can contribute through Fish Tool Use, where divers and marine observers are encouraged to share footage or descriptions of wrasse behavior. With more data, scientists can explore whether anvil use is common across the family or limited to just a few clever species.

For now, wrasses have made one thing clear: we’ve underestimated fish. Not only are they smart, but they’re capable of innovation, planning, and creative problem-solving.

Tool use may no longer be the preserve of a few gifted animals. It may be far more widespread – if we only care to look.

The study is published in the journal Coral Reefs.

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