Coordinated Attacks Through Changing Body Color: The Striped Marlin

The striped marlin Kajikia audax is a large predatory fish and one of the top predators of the open ocean. It possesses remarkable swimming speed and a long, sharp bill. During hunting events these fish often appear in groups. Yet such high-speed predation creates a potential problem: when several predators armed with dangerous bills rush toward the same prey, how do they avoid injuring one another?

Previous observations have shown that striped marlin hunting in groups typically attack a school of fish in turns. At any given moment, only one individual charges into the prey school. This raises an important question: how do these predators coordinate the order of attacks so that they do not collide with one another during high-speed strikes? A recent study has now provided an answer.

A research team led by Alicia Burns from Humboldt University of Berlin used drones to film the hunting behavior of striped marlin. When the researchers later examined the footage, they noticed a striking pattern. Just before launching an attack, a marlin's body suddenly became brighter, and once the attack ended its coloration returned to normal. This observation suggested that the rapid change in body color might function as a signal to other marlin, effectively announcing that an attack is about to occur.

A striped marlin changing its body coloration as it prepares to charge into a school of sardines（Courtesy of Alicia Burns）

To investigate this possibility, the researchers analyzed twelve video clips. Each clip contained two separate attacks on a sardine school by two different marlin. The team compared the stripe contrast of attacking individuals with that of randomly selected non-attacking marlin in the same footage. Their analysis confirmed that the color change was strongly associated with attack behavior.

However, this correlation alone did not prove that the color change was intentional. It could potentially have been a physiological side effect of the attack itself—for example, changes caused by adrenaline release during rapid acceleration. To test this alternative explanation, the researchers compared attacks directed at dense sardine schools with attacks directed at single, isolated sardines. If the color shift were merely a physiological by-product of acceleration, the same color change should occur in both situations.

The observations showed otherwise. When striped marlin attacked a solitary fish, their body coloration hardly changed at all. This indicates that the color change is a deliberate behavior rather than a passive physiological effect. The researchers suggest that attacks on fish schools usually last longer and therefore carry a greater risk that another marlin might interrupt the strike. By brightening their stripes before attacking, a marlin may effectively signal to nearby conspecifics: now it is my turn.

The color change may also serve a second function. The intensified stripe contrast might visually confuse the prey school. Strong contrasting patterns can create a dazzling effect that interferes with an observer's ability to track movement. If sardines struggle to follow the trajectories of nearby individuals, the coordinated escape responses of the school may break down, making them more vulnerable to predation.

Although striped marlin were previously known to possess the ability to change body color, this study is the first to directly link that ability with both hunting behavior and social coordination. The findings reveal that striped marlin may possess a more complex communication system than previously recognized.

The researchers hope that future work will explore whether these rapid color changes are used in other behavioral contexts. The team has also obtained footage of other predatory fish—such as different billfish species and mahi-mahi—while they hunt. Preliminary observations suggest that these species may exhibit even more complex and varied color changes during predation, but those results will need to await future studies.

Author: Bai Leng

Reference:

Burns, A., Licht, M., Heathcote, R. J. P., Krause, J., Hansen, M. J. (2024). Rapid color change in a group-hunting pelagic predator attacking schooling prey. Current Biology.

（Paid content. Unauthorized reproduction or use is prohibited.）