Fish use a 'motion dazzle' strategy to outsmart predators

The humbug damselfish, known for its striking black-and-white stripes, has mastered a unique form of camouflage that goes beyond blending into its environment.

While stillness helps many creatures evade predators, the highly mobile damselfish adds another layer of protection through a technique called “motion dazzle,” which confuses predators when the fish are in motion.

This clever strategy, along with their adaptability to different backgrounds, allows the fish to outsmart their predators and thrive in coral reef habitats.

Defense strategy of the humbug damselfish

New research has uncovered a fascinating dual defense mechanism used by animals with high-contrast body patterns.

When stationary, these patterns provide effective camouflage. However, once in motion, they create a perplexing motion dazzle effect that confuses predators, helping prey avoid being eaten.

Damselfish change with their environment

The study was conducted by Dr. Louise Tosetto, Professor Nathan Hart, and Dr. Laura Ryan from Macquarie University’s School of Natural Sciences. The research is the first to show how humbug damselfish have mastered this intriguing defense strategy.

“Our findings show that humbug damselfish adapt their behavior based on their environment,” explained Dr. Tosetto.

“In their natural habitat, when they encounter backgrounds resembling their own striped patterns, such as branching corals, they tend to decrease their movement and move closer. This likely helps them blend in, becoming invisible to predators.”

“However, when feeding outside the coral colony – where camouflage is less effective – they increase their movement and rely more on the confusing effects of their stripes, known as motion dazzle.”

Focus of the research

To explore this extraordinary anti-predator behavior, the research team conducted an extensive study.

The experts filmed humbug damselfish swimming against various striped backgrounds in tanks and used computer models to simulate how predators, such as coral trout, would perceive the fish’s movements.

Additionally, the team incorporated anatomical data from the retinas of the damselfish to better understand how these fish might perceive different environmental patterns.

Using motion dazzle to deter predators

The team discovered that humbugs adjust their movement when against backgrounds where predators find it difficult to detect them.

The fish moved closer to these backgrounds and intensified their movement, creating confusing motion signals that likely helped them evade predators.

Conversely, when the background had clearer, broader stripes, the humbug damselfish benefited in two ways.

First, their body edges became less distinct, making detection harder. In addition, the combination of their stripes with the background created confusing motion signals – making it difficult for predators to accurately judge their speed or direction.

“This suggests that humbugs can perceive different backgrounds and might change their behavior to improve their protection from predators,” said Dr. Tosetto.

Complex anti-predator strategies

The study provides new insights into the intricate anti-predator strategies employed by these small fish.

“This is an essential baseline study that offers valuable insights into the motion dazzle phenomenon,” said study senior author Dr. Ryan.

She emphasized that further research should explore how environmental factors, such as water’s light-filtering properties and interactions with other damselfish, might influence motion dazzle.

“The humbug damselfish provides a perfect model for exploring these important questions,” noted Dr. Ryan.

Group camouflage in humbug damselfish

The humbug damselfish doesn’t just rely on its own stripes for protection; it also benefits from living in tightly-knit social groups.

These fish often swim in schools within the shelter of branching corals, where their collective movement can amplify the motion dazzle effect.

By moving together, their alternating black and white patterns create even more confusion for predators trying to single out one fish from the group.

This behavior is crucial during feeding, as it allows the damselfish to move in synchrony and reduce the chance of being targeted by predators.

The collective movement can disrupt a predator’s ability to track an individual, making the whole group safer.

Research suggests that this social camouflage adds an extra layer to their survival strategy, highlighting the complexity of how these small fish evade threats.

The study is published in the journal PeerJ.

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