Okinawa: Visual signals, such as colour patterns are an important communication medium for anemonefish, researchers from the Okinawa Institute of Science and Technology have recently elucidated.
The researchers found how the patterns on anemonefish — which are conspicuous white bars against an orange, red, or black background — influence their aggressive behaviour and possibly determine the colour patterns of cohabitating fish. The behavioural responses and social interactions ultimately govern community structure within the surrounding coral reef ecosystem.
Colour patterns on fish are visually appealing, but their function goes much beyond providing aesthetic appeal to their beholders. These patterns are governed by multiple factors such as predators, prey, competition, and the choice of mate.
In highly transparent water around coral reefs, visual signals such as colour patterns are used as important communication tools. Many fish leverage these patterns to monitor their interactions with fish of their own species or different species, including mimicry, identification, camouflage, and courtship. In fact, fish inhabiting coral reefs produce a broad range of colour patterns—bars, stripes, and spots—and have the most diverse pigment cell types among all vertebrates.
One such species—the anemonefish, inhabits sea anemones right after exiting the larval stage and is characterized by white bars on an orange, red, or black background. However, the exact evolutionary function of these bars in anemonefish has not been understood clearly.
Now, marine biologists including Dr Kina Hayashi and Dr Vincent Laudet from the Marine Eco-Eco-Devo Unit at Okinawa Institute of Science and Technology (OIST), and Dr Katsunori Tachihara and Dr James Davis Reimer from The University of Ryukyus have explored how colour patterns are associated with frequency of aggressive behaviour displayed by anemonefish in coral reefs. The findings from this study, which was led by Dr Hayashi, were published in Proceedings of the Royal Society B on October 5, 2022. “Our findings are the first to highlight that banding patterns of fish in the vicinity of an occupied anemone influence the behaviour of other resident fish,” says Dr Hayashi.
For the study, the team conducted field surveys at 5 different sites on the Ryukyus Archipelago, between September 2020 and October 2021. They targeted the Amphiprion ocellaris species of anemonefish, which inhabits the Stichodactyla gigantea species of anemone, in each study area. Furthermore, they studied the fauna residing in 49 S. gigantea individuals and 49 scleractinian corals closest to these anemones. “Although anemonefish aggressively defend their host anemone, a host anemone can still be a temporary home for other fish seeking refuge,” says Dr Hayashi.
The team had previously observed that other fish residing in these anemone hosts had stripes or spots, but none had vertical bar patterns. “We hypothesized that the anemonefish were playing gatekeeper. It was possible they were excluding fish based on colour patterns,” adds Dr Hayashi.
To confirm this hypothesis, the team conducted a behavioural experiment to document the aggressive behaviour of anemonefish by dangling plastic fish toys close to an anemonefish colony. They painted these toys either with vertical white bars or with horizontal white stripes to present them to the anemonefish. Instances of “chasing” or “biting” them were recorded as aggressive behaviour.
The findings indicated that no fish with vertical bars sought shelter in host anemones. However, a variety of species bearing this colour pattern were found in the surrounding corals. Specifically, only 39% of the anemones were used as shelter by fish other than anemonefish, while 100% of the corals were used as shelter by fish of other species. True to character, the anemonefish responded aggressively when presented with the fish toys containing vertical bars. In fact, the duration of this aggressive behaviour was also much longer towards the vertical bar model than towards the horizontal stripe model.
Dr Kina Hayashi is a Postdoctoral Researcher in the Marine Eco-Evo-Devo Unit the at Okinawa Institute of Science and Technology (OIST). Her research has focused on the population dynamics, community structure, and coexistence mechanisms of the anemonefish in the Ryukyu Islands. She is also interested in species recognition of the anemonefish and is presently engaged in a project investigating the relationship between the territorial behaviour of anemonefish and the colour pattern of coral fish. She has published nine articles in peer-reviewed journals since 2018.
The study was partly supported by a Grant-in-Aid for Scientific Research from the Japan Society for the Promotion of Science (Grant No.: 20J11845) and a research scholarship from the OIST Kicks program.
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