When you hear the term “intelligent animal,” which species comes to mind? Most likely, you’re picturing an animal that bears a strong resemblance to us: a primate like an orangutan or chimpanzee. Perhaps it’s a dolphin or octopus, or maybe even a bird such as a crow or parrot. A fish likely wouldn’t even be in the running; we as humans tend to view them as vastly lesser creatures in their strange marine environment, driven by instinct rather than intelligence. The idea of fish having a sense of self, not to mention a culture or the capacity for learning, may seem far-fetched. But emerging research from trailblazing marine scientists is shedding light on patterns of behavior and surprising cognitive abilities in fish that challenge our perception of intelligence and ecosystem complexity. In order to fully grasp the importance of the delicate balance of our coral reefs, it is essential for us to understand the brains and behaviors of some of their most influential members: fish.
One of the more interesting and highly studied examples of a fish species with surprising cognitive abilities is the bluestreak cleaner wrasse, Labroides dimidiatus. Just like the aforementioned primates, dolphins, and octopuses, cleaner wrasse are able to pass the mirror self-recognition test (Kohda, 2022). This test, which determines whether the animal is capable of recognizing their own reflection, implying that they have cognitive self-awareness, is performed by testing if an animal can use a mirror to try and locate and remove a spot from its body. Cleaner wrasse have consistently passed this test under a variety of circumstances, but more importantly, a new study suggests that they may even be able to use the mirror as a tool to inform their offensive strategies against differently sized competing fish. Only after being exposed to the mirror did the cleaner wrasse use their own size to gauge whether to attack other fish, hesitating more when faced with a larger opponent. This implies that they could be capable of metacognition, the ability to reflect on their thought process to plan and make decisions (Kobayashi, 2024). These findings become especially relevant when we examine their incredibly complex mutualistic relationships with other fish in their reef systems. Far from having “the one-second memory of a goldfish,” it seems that wrasse possess surprising powers of recognition, memory, and decision-making.
Bluestreak cleaner wrasse maintain and operate cleaning stations in groups, at which they provide a necessary service to larger reef-dwellers by consuming their dead skin and parasites. Under observation, these wrasse have demonstrated that they are not only able to remember a vast number of previous visitors to their stations, but also are capable of remembering when these fish visited them, clearly preferring to serve new clients over repeat visitors (Freixial, 2018). They exhibit Machiavellian behavioral tendencies, travelling to other cleaning stations and biting their rival station’s clients, in an attempt to decrease business, and have complex understandings of the relationships between other fish. If attacked by a dissatisfied client, the cleaner wrasse will first attempt to placate them by rubbing their fins and performing a kind of dance, and then swim towards a known predator of their attacker in hopes of receiving protection (Bradley, 2024). These fascinating social techniques are developed through “horizontal” learning; the fish observe the behavior of other members of their ecosystem, adapting to perceived relationships and the cues of peers within their species. But “vertical” learning, the transfer of knowledge down through generations, also plays a massive role in the behavior of many fish species, especially in the highly social and complex ecosystem of a coral reef (Soares, 2017).
If we shift our focus over in the phylogenetic tree of the wrasse family Labridae, we find the L. dimidatus’s cousin, Thalassoma bifasciatum, or bluehead wrasse, notable for its impressive capacity for social and generational learning. These fish have specific migratory paths and breeding grounds, which remain constant throughout new generations, as is to be expected. But in addition, researchers found under observation that even tiny or peculiar and unnecessary movements were copied between generations, including body pitches and rolls, implying that imitation is driving the behavior rather than pure instinct. Amazingly, one bluehead wrasse study found that across 22 locations and over 12 years of observation, not a single one of the breeding locations was lost, and no new ones ever emerged.
Generational learning is not a trait that is unique to the bluehead wrasse; the copper sweeper, French grunt, and brown sturgeonfish are among the most common fish studied for this ability (Brown, 2025). Generational and social learning is crucial for a huge number of fish species, but environmental changes which outpace the natural process of evolution make long-lived, generationally informed fish particularly vulnerable. Overfishing, pollution, rising temperatures, and reef erosion all result in dwindling numbers of older fish, which are less resilient to extreme environmental stressors. Loss of generational knowledge accelerates the damage a rapidly changing environment does to breeding patterns, migration paths, and a myriad of other crucial animal processes.
Currently, there is limited research on this type of cognition and learning in fish; it is likely that more complexities exist in coral reef ecosystems than we could even imagine. However, these ecosystems are rapidly changing and dwindling. The pursuit of understanding animal cognition and behavior tasks us with releasing our preconceived notions of intelligence, and dispensing with our tendencies to measure nonhuman life forms by human parameters. Only when we reach that point will we be able to appreciate and understand what it is we are fighting to save.
References
Bradley, J. (2024). Deep Water. HarperCollins.
Brown, C., & Webster, M. (2025). Fishy culture in a changing world. Philosophical Transactions of the Royal Society B Biological Sciences, 380(1925). https://doi.org/10.1098/rstb.2024.0130
Clague, G. E., Newport, C., & Grutter, A. S. (2011). Intraspecific cleaning behaviour of adult cleaner wrasse, Labroides dimidiatus (Perciformes: Labridae). Marine Biodiversity Records, 4. https://doi.org/10.1017/s175526721100056x
Freixial, C., Vasco-Rodrigues, N., Baylina, N., & Modesto, T. (2018). Cleaning behaviour of adult bluestreak cleaner wrasse, Labroides dimidiatus (Perciformes: Labridae), in Oceanário de Lisboa. Frontiers in Marine Science, 5. https://doi.org/10.3389/conf.fmars.2018.06.00043
Kobayashi, T., Kohda, M., Awata, S., Bshary, R., & Sogawa, S. (2024). Cleaner fish with mirror self-recognition capacity precisely realize their body size based on their mental image. Scientific Reports, 14(1). https://doi.org/10.1038/s41598-024-70138-7
Kohda, M., Sogawa, S., Jordan, A. L., Kubo, N., Awata, S., Satoh, S., Kobayashi, T., Fujita, A., & Bshary, R. (2022). Further evidence for the capacity of mirror self-recognition in cleaner fish and the significance of ecologically relevant marks. PLOS Biology, 20(2), e3001529. https://doi.org/10.1371/journal.pbio.3001529
Soares, M. C. (2017). The neurobiology of mutualistic behavior: The cleanerfish swims into the spotlight. Frontiers in Behavioral Neuroscience, 11. https://doi.org/10.3389/fnbeh.2017.00191