DIVING NEWS
Cleaner wrasse: the first ‘self-aware’ fish
Picture: Elias Levy.
Fish may sometimes give the impression of admiring themselves in underwater camera dome-ports, though they are as likely to attack them as if thinking their reflection is a rival.
But according to new research into cleaner wrasse, this fish exhibits all the signs of recognising that it is seeing itself in its reflection.
This self-awareness, observed in bluestreak cleaner wrasse (Labroides dimidiatus) by researchers from Osaka City University, makes it the first fish to be considered in the same light as certain mammals such as dolphins and some birds. These animals have passed a classic test for determining self-awareness that others such as dogs, cats and octopuses fail.
1 September 2018
The ability to perceive and recognise a reflected mirror image as self is considered a hallmark of cognition, and the researchers say that cleaner wrasse pass through all the phases of the mirror self-recognition or MSR test, which dates back almost 50 years.
The fish first reacts by attacking the reflection, then repeats idiosyncratic behaviour towards it such as “dancing”, before returning frequently to view its reflection.
Once the subject is familiar with the mirror, the test involves placing an unfamiliar mark on its body, so that it recognises in the mirror that something has changed and attempts to touch or remove it.
When a coloured tag was placed on a wrasse’s head, it would try to remove it in the presence of a mirror but would not do so if the mirror was absent, or when a transparent tag was used.
The cleaner wrasse was chosen as a subject because it is known for its ability to spot parasites on other fish and use its mouth to pick them off.
The experiments were carried out on 10 fish in separate tanks with their own mirrors. The tags, in the form of a gel, were applied to eight of the fish and all but one responded by trying to scrape it off.
Although the cleaner wrasse passed the MSR test, the scientists have also called into question the validity of the long-established test itself, in that it remained possible that rather than exhibiting instinctive self-awareness, the wrasse came to learn over time that the mirror represented its body.
The study is published in bioRxiv.
