Color patterns influence aggression among reef fish

A new study led by the Okinawa Institute of Science and Technology (OIST) has found that visual signals, such as color patterns, are an important communications medium for anemonefish residing around coral reefs. By investigating how the patterns on anemonefish – conspicuous white bars against orange, red, or black backgrounds – influence their aggressive behavior toward cohabitating fish, the experts discovered that these color patterns drive fish community structure within the surrounding coral reef ecosystem.

Scientists have long known that, in highly transparent water around coral reefs, visual signals such as color patterns are employed as critical communication tools. For instance, many fish use these patterns to monitor their interactions with fish of their own or different species during processes such as mimicry, identification, camouflage, or courtship. In fact, coral reef fish have the most diverse pigment cell types among all vertebrates, producing a wide range of color patterns.

One such species, the anemonefish, inhabits sea anemones right after exiting the larval stage, and is colored with white bars on an orange, red, or black background. The researchers conducted field surveys at five different sites on the Ryukyus Archipelago (between September 2020 and October 2021) to explore how color patterns are associated with the frequency of aggressive behaviors. 

While other fish residing in these anemone hosts had stripes or spots, none of them had vertical bar patterns. “Although anemonefish aggressively defend their host anemone, a host anemone can still be a temporary home for other fish seeking refuge,” said study lead author Kina Hayashi, a marine biologist at OIST. “We hypothesized that the anemonefish were playing gatekeeper. It was possible they were excluding fish based on color patterns.”

To test this hypothesis, the scientists conducted a behavioral experiment to document aggressive behavior of anemonefish by dangling plastic fish toys – painted either with vertical white bars or with horizontal white stripes – close to an anemonefish colony. As expected, the anemonefish responded aggressively when presented with fish toys sporting vertical bars. 

“It is likely that the fish community around host anemones is affected by the differences in the frequency of aggressive behavior of anemonefish towards intruders with certain color patterns,” Dr. Hayashi explained.

“Elucidating the relationship between color pattern recognition ability and aggression displayed by anemonefish will provide useful insights on the mechanisms of coexistence employed by coral reef fish, and the roles that their patterns play. In regions with coral reefs, conserving species and their habitats is crucial, which is possible if we understand the interactions between these inhabitant species,” she concluded.

The study is published in the journal Proceedings of the Royal Society B Biological Sciences.

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By Andrei Ionescu, Earth.com Staff Writer