Tool Use in Fish Documented

For decades, the general consensus on fish intelligence was dismissive. Most people assumed fish possessed little memory and operated purely on instinct. However, recent photographic and video evidence has shattered these assumptions. Tuskfish have been documented systematically smashing clams against rocks to open them. This behavior suggests a level of cognitive ability and foresight previously thought to be the exclusive domain of primates, birds, and mammals.

The Tuskfish and the Clam

The star of this scientific breakthrough is the tuskfish, specifically members of the genus Choerodon. The most famous footage features the orange-dotted tuskfish (Choerodon anchorago) and the blackspot tuskfish (Choerodon schoenleinii).

Researchers, including Giacomo Bernardi from the University of California, Santa Cruz, and Culum Brown from Macquarie University in Australia, have observed this behavior in locations ranging from Palau to the Great Barrier Reef. The behavior is not accidental. It is a deliberate, multi-stage process that requires planning.

The fish does not simply stumble upon an open meal. It identifies a clam or cockle buried in the sand. After digging it up, the tuskfish faces a problem: the shell is too hard to crush with its jaws alone. To solve this, the fish carries the bivalve in its mouth and swims to a specific location known as an “anvil.”

The “Anvil” Technique

The term “anvil” is used by biologists to describe a hard surface used as a tool to break open objects. The tuskfish selects a specific rock or piece of coral for this purpose. The process involves several distinct steps that demonstrate logical sequencing:

Excavation: The fish locates the buried prey and blows water or digs to release it.
Transport: The fish carries the prey in its mouth to the chosen anvil site. This site may be several meters away from where the food was found.
Orientation: The fish releases the clam and positions itself precisely.
Impact: Using rapid, lateral snaps of its head and body, the fish picks up the clam and smashes it against the rock.
Consumption: Once the shell fractures, the fish accesses the soft meat inside.

This is not a random act of aggression. The fish will repeatedly strike the clam against the same spot on the rock until it breaks. If the clam slips, the fish retrieves it and tries again.

Redefining "Tool Use" in Science

The documentation of tuskfish behavior has forced a debate regarding the definition of tool use. Historically, strict definitions required an animal to hold an object (the tool) and manipulate it to alter another object. For example, a chimpanzee holding a rock to crack a nut, or a crow bending a wire to hook a worm.

In the case of the tuskfish, the fish cannot hold a hammer because it lacks hands. Instead, it holds the object it wants to break and applies force against a stationary tool (the rock).

Critics initially argued this did not count as true tool use. However, leading experts in fish cognition argue that the cognitive demand is identical. The fish is using an external object (the rock) to achieve a goal that its own body cannot achieve alone. This falls under the functional definition of tool use. The fish understands the physical properties of the rock and understands that force is required to access the food.

Cognitive Implications

The ability to use tools implies several high-level cognitive traits:

Goal-directed behavior: The animal understands the desired outcome before starting the task.
Flexibility: If the rock is not hard enough or the angle is wrong, the fish adjusts its strategy.
Memory: Tuskfish return to the same anvil rocks repeatedly. They remember where the useful tools are located within their territory.

Beyond the Tuskfish: A Pattern of Intelligence

While the tuskfish provides the most visual and dramatic example of tool use, it is not the only fish displaying high intelligence. The documentation of the tuskfish has encouraged scientists to look closer at other species.

The Archerfish The archerfish is known for hunting land-based insects by spitting a jet of water to knock them into the water. This requires complex physics calculations. The fish must account for the refraction of light at the water’s surface, the speed of the target, and the force of gravity on the water jet. They learn to adjust their aim based on distance and angle.

Cleaner Wrasse The cleaner wrasse has passed the “mirror test,” a classic experiment used to determine self-awareness. When researchers placed a colored mark on the fish’s throat (visible only in a mirror), the fish attempted to scrape the mark off against a rock after seeing its reflection. This suggests they understand the reflection is themselves, a trait previously attributed only to humans, great apes, dolphins, and magpies.

What This Means for Animal Welfare

The confirmation that fish can use tools and possess long-term memory challenges how humans interact with aquatic life. If fish have the capacity for planning and problem-solving, their capacity for suffering or boredom may be higher than previously estimated.

Organizations advocating for animal welfare are using this data to argue for better conditions in aquaculture and the aquarium trade. The scientific community is moving away from the idea of fish as simple reflex-machines and acknowledging them as complex vertebrates with distinct personalities and cognitive skills. The tuskfish, with its persistent smashing of clams, has become the icon of this shifting perspective.

Frequently Asked Questions

What specific fish species use rocks to open clams? The behavior is most commonly documented in the Choerodon genus, particularly the orange-dotted tuskfish (Choerodon anchorago) and the blackspot tuskfish (Choerodon schoenleinii).

Is this considered true tool use? Yes, most modern biologists consider this tool use. While the fish does not hold the tool in a hand, it utilizes an external object (the anvil rock) to alter another object (the clam) to achieve a specific goal.

Where does this behavior take place? This behavior has been filmed and documented in the tropical waters of the Indo-Pacific region, including the Great Barrier Reef in Australia and the waters surrounding Palau.

Do tuskfish learn this behavior or is it instinct? It appears to be a mix of both, but there is a strong learned component. Younger fish are less efficient at the process and improve over time. The fact that they return to specific rocks suggests they learn and remember the best locations for “anvils.”

How strong are the tuskfish? They are surprisingly powerful. The lateral snap of the head generates significant force. This movement allows them to crack thick shells that would be impossible to break with jaw pressure alone.