Long considered the exclusive domain of primates and birds, tool use has now been observed in fish. A study reveals that this surprising ability is found exclusively in wrasses, a family of reef fish.
Sequence of actions during an anvil use. A yellowhead wrasse (Halichoeres garnoti) strikes a brittle star arm against rubble by swinging its head from left to right.
Underwater observations and contributions from amateur divers have identified five species of wrasses using rocks as anvils to crack open shellfish. These findings, published in
Coral Reefs, challenge our understanding of animal intelligence.
A precise and energy-intensive technique
Wrasses grasp their prey with their mouths and violently slam them against rocks. This lateral movement requires significant energy expenditure and is often repeated multiple times. Despite this, some individuals lose their prey to opportunistic competitors.
Stone selection appears deliberate, though the fish adapt their approach based on their environment. Unlike primates, wrasses show no marked laterality: they use both sides of their body equally. This flexibility may explain their success.
Targeted prey include crabs, sea urchins, and starfish. For smaller wrasses, this technique provides access to otherwise unreachable resources. However, predation risks during the operation remain unknown.
An underestimated intelligence
Wrasses stand out due to their specialized mouth morphology and varied diet. Their ability to use tools may stem from these adaptations. Yet, not all individuals adopt this behavior, suggesting a social learning component.
The study raises a key question: is this knowledge innate or acquired? Ongoing experiments aim to determine whether wrasses can learn through imitation. The results could shed light on the evolution of cognitive abilities in fish.
This discovery expands the range of tool-using animals, previously limited to a few "superior" species. It invites us to reconsider the intelligence of marine creatures, which remains largely unexplored.
Going further: how to define tool use in animals?
Tool use involves manipulating an external object to accomplish a specific task, such as feeding or defense. In wrasses, striking a shell against a rock clearly falls into this category.
This skill is not instinctive in all species. It often requires a combination of motor and cognitive abilities, including planning and environmental adaptation.
The criteria for classifying a behavior as "tool use" remain debated. Some scientists include simple actions, while others demand demonstrated complexity.
Article author: Cédric DEPOND