For a small fish, a coral reef is a dangerous place, full of hungry predators. Many fish protect themselves by staying still, and using some form of camouflage to blend in with the background. But, sitting still all the time isn’t practical, and so some fish also use special movement strategies and the right kinds of camouflage to hide while moving.
The humbug damselfish is an example. It’s usually about three inches long, and it lives in coral reefs in the Pacific and Indian Oceans. It moves frequently to browse for food. In 2024, a team of biologists from Australia published a study of its hiding strategy.
The humbug damselfish’s body might not seem very well camouflaged. It is covered by several striking black and white vertical stripes. But when the animal is still, these stripes actually keep it well hidden among the vertical branches of the corals among which it lives. When it moves, the biologists found that the stripes create a visual phenomenon called ‘motion dazzle’ which confuses predators attempting to judge its speed and direction of movement.
The researchers used a computer model to simulate how predators like a coral trout might see this movement. In the lab, they studied how damselfish moved against background patterns of stripes with different orientations and widths. These simulated different natural backgrounds. The researchers found that damselfish could see the backgrounds and adjust their movements to maximize the motion dazzle effect for that background as seen by the predator. They showed that the fish use complex strategies to actively hide from predators. The biologists hope to learn much about vision and animal camouflage by studying this little fish.
We would like to give a special thanks to the reviewer of today's episode: Rafael Duarte, from the University of Aveiro, in Aveiro, Portugal.
Further Reading
- Humbug damselfish use ‘motion dazzle’ to evade predators, ScienceDaily.com
- Fish use a ‘motion dazzle’ strategy to outsmart predators, Earth.com
- Humbug damselfish: Masters of ‘motion dazzle’ defense, ScienceBlog.com
- Zebras of the fish world use their stripes to dazzle predators, Cosmosmagazine.com
- Why damselfish use ‘motion dazzle’ to evade predators, Macquarie University
L. Tosetto, N. S. Hart, and L. A. Ryan, 2024 Dazzling damselfish: Investigating motion dazzle as a defense strategy in humbug damselfish (Dascyllus aruanus) PeerJ 12:e18152 http://doi.org/10.7717/peerj.18152.