This footage was filmed and produced 1 February 2024.

[Credit: Kina Hayashi]

New findings from the Okinawa Institute of Science and Technology (OIST) challenge the common perception of fish as simple creatures, suggesting that they possess a level of cognition that is often underestimated. Researchers at OIST conducted a study on clown anemonefish, famously depicted in the movie "Finding Nemo," and discovered that these fish can recognize different species of anemonefish based on the number of white bars on their bodies.

Led by Dr. Kina Hayashi from the Marine Eco-Evo-Devo Unit at OIST, the research team observed a colony of clown anemonefish in their sea anemone home, studying their reactions to intruders. The study, published in the Journal of Experimental Biology, found that the clown anemonefish display the highest frequency and duration of aggressive behaviors towards intruders with three vertical bars, similar to their own appearance. In contrast, fish with one or two bars received less aggression, and those without any vertical bars were treated with the least hostility. This suggests that the clown anemonefish are capable of counting the number of bars to recognize the species of intruders.

To investigate further, the researchers conducted experiments involving immature clown anemonefish raised in the lab. They placed different species of anemonefish, with varying numbers of white bars, in small cases within a tank containing a clown anemonefish colony. The study also involved presenting the colony with plastic discs painted with anemonefish coloration. The results consistently demonstrated that the fish exhibited the most aggressive behaviors towards intruders or models with three vertical bars, implying that the count of vertical white bars is a pivotal factor in determining their level of aggression.

The study also revealed a strict hierarchy within clown anemonefish colonies. Typically, a colony consists of one alpha female, one beta male, and several gamma juveniles, with social status determined by size differences. The largest juvenile assumes the role of the alpha and defends the colony against intruders, ensuring a stable social order.

Dr. Hayashi emphasizes the importance of understanding marine ecosystems, pointing out that the study underscores the need to preserve fragile coral reefs, where clown anemonefish reside. With their surprising abilities to count bars and establish social hierarchies, these fish serve as a reminder that many extraordinary animal behaviors remain undiscovered in threatened ecosystems.

This research sheds new light on the cognitive capabilities of fish, challenging longstanding assumptions and highlighting the vast potential for further discoveries in the fascinating world of marine life.