Research revisiting mirror experiments with cleaner wrasse addresses earlier criticisms and strengthens evidence that these reef fish may recognise their own reflection.
Cleaner wrasse continue to challenge assumptions about fish intelligence. (Illustration: Peter Symes / AI; Wrasse image: François Libert François Libert, CC BY-NC-SA 2.0)
Cleaner wrasse, small reef fish known for removing parasites from other fish, continue to challenge assumptions about fish intelligence. A new study, published in Scientific Reports, revisits earlier mirror experiments and provides new insights into how these fish interpret their reflections.
X-Ray Mag has previously reported on research suggesting that cleaner wrasse (Labroides dimidiatus) may possess unexpectedly advanced cognitive abilities, including the possibility of recognising themselves in mirrors. The latest study helps clarify how the fish respond to mirror images and what their behaviour may mean.
Earlier discoveries
Cleaner wrasse first attracted global attention in behavioural science in 2019, when experiments suggested the species might pass a modified version of the mirror self-recognition test, a classic behavioural experiment used to investigate self-awareness in animals.
In those experiments, fish were marked on parts of their bodies that could only be seen via a mirror. After observing the marks in their reflection, some fish attempted to scrape the marks off against nearby surfaces.
The findings prompted considerable discussion among scientists. Some researchers interpreted the behaviour as evidence of self-recognition, while others suggested the fish might simply be reacting to what they perceived as another individual in the mirror.
Addressing the criticisms
The new study examines these questions more closely by analysing how cleaner wrasse interpret mirror images, and how they respond to marks seen in their reflection.
The researchers found that the fish appeared to treat the reflection as their own body, rather than as another fish. Their responses were directed specifically at marks visible on the reflected body, behaviour consistent with recognising that the reflection corresponded to themselves.
By examining these behavioural responses in greater detail, the study addresses one of the key criticisms of earlier experiments—that the fish might merely be responding socially to another fish in the mirror.
Why cleaner wrasse are special
Cleaner wrasse are particularly interesting to scientists because of their complex social behaviour on coral reefs. At so-called cleaning stations, the fish interact with dozens of different species, removing parasites and dead tissue from larger “client” fish.
These interactions require recognising individual clients, maintaining cooperation and sometimes even negotiating conflicts when cleaners are tempted to cheat by taking bites of mucus instead of parasites. Because of this sophisticated social environment, researchers have long suspected that cleaner wrasse may possess unusually advanced cognitive abilities for fish.
Earlier reporting in X-Ray Mag
X-Ray Mag has previously covered several studies exploring the cognitive abilities of cleaner wrasse, including reports on an indication of fish cognitive powers, experiments suggesting eye contact in fish reveals self-awareness, research showing that a fish recognises itself in photographs, and broader discussions of the remarkable intelligence of fish. Together, these studies are gradually reshaping how scientists view the cognitive abilities of fish.
