Study reveals lateralisation in fish

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Researchers from the University of Edinburgh have demonstrated that lateralisation can occur in the brains of fish.

The research showed that fish which have to cope with the threat of predators would process information on a particular side of the brain, in a similar way that humans might be right- or left-handed.

The fish involved in the research are among a growing number of animal species in recent years that have been found to have lateralisation of the brain.

Brain lateralisationThe research was carried out on a small livebearer called the Bishop fish, Brachyraphis episcope, which were sourced from areas of high and low predation in Panama.

The fish were bred in captivity, and in the laboratory both the wild-caught parents and their offspring had behavioural tests carried out on them.

The results of these tests were very interesting. They demonstrated that the wild-caught fish from areas of high predation would watch objects with a specific eye, and so would use a specific hemisphere of the brain.

Their captive-bred offspring also showed a preference for a specific eye in the tests. These results demonstrate strong lateralisation in the brains of both fish.

Culum Brown, who is now at Macquarie University in Sydney, explains that "for animals that have to cope with many predators, it is an advantage if they can use one hemisphere to keep an eye on predators while they use the other hemisphere to do other things."

Remarkably though, the wild-caught fish from areas of low predation, and their captive-bred offspring, appeared to show little notable preference for either eye.

This suggests that the brains of these fish are not very lateralised, and it is suggested that they may have simply not refined their lateralisation as they have little use for it.

The fact that the captive-bred offspring gave similar results to their wild-caught parents in both cases "shows that a tendency for brain splitting can be inherited," suggests Victoria Braithwaite of the University of Edinburgh.

Left- or right-handed?However, there was one point of confusion. In the tests on fish from the areas of high predation, the wild-caught fish would use their left eye, whereas their captive-bred offspring would use their right eye " which means that, although they would both use a single side of the brain, they were using different sides!

Braithwaite suggests that perhaps the "lab-reared fish could process information about novel objects in the left brain because they feel more comfortable" than their wild-caught parents, who would be more wary due to predatory experience, meaning that the side of the brain used "is a learned thing."

The tests carried out involved the fish swimming towards a slatted barrier " through which they would see a novel object (a yellow cross), another Bishop fish, or nothing.

Should the fish swim past the barrier on the left, it would mean that they had kept their right eye on what they had seen, and if they swam past on the right then it meant they had kept their left eye on it.

During the testing, the greatest reactions in the fish were observed when the novel object was used. The fish had no previous experience of this object, and as a result were more wary.