Laterality is linked to personality in the black-lined rainbowfish, Melanotaenia nigrans

Emotions such as fear in vertebrates are often strongly lateralised, that is, a single cerebral hemisphere tends to be dominant when processing emotive stimuli. Boldness is a measure of an individual's propensity to take risks and it has obvious connections with fear responses. Given the emotive nature of this well-studied personality trait, there is good reason to suspect that it is also likely to be expressed in a single hemisphere. Here, we examined the link between laterality and boldness in wild and captive-reared rainbowfish, Melanotaenia nigrans. We found that fish from the wild were bolder than those from captivity, which might be a reflection of the differences in the level of predation pressure experienced by the two populations. Secondly, we found that non-lateralised fish were bolder than strongly lateralised fish. In addition, differences in boldness scores between left- and right-biased fish were revealed. We suggest that variation in cerebral lateralisation contributes to the persistence of individual differences in boldness scores in animal populations.