Are fish 'rightie' or 'leftie'?

Japanese researchers have identified the development of behavioural laterality or left- or right-handedness and attack side preference in a scale-eating cichlid called Perissodus microlepis from Africa's Lake Tanganyika.

The study found that as the fish grow, they develop a preference for either being a "righty" or a "lefty" based on which side of their mouth is more effective at acquiring food. Both "lefties" and "righties" exist in the species.

The direction of attack during scale eating is tightly linked to each individual's mouth asymmetry in adulthood.

"This is truly an important study because it allowed us to observe mouth direction development with age and the relationship between behavioural laterality and mouth asymmetry in these fish," said lead author Yuichi Takeuchi of Toyama University.

Measurements of the lower jawbone of the scale-eating fish revealed a gradual increase in mouth asymmetry -- i.e., skewed to the left or right -- as the fish age.

For instance, very young fish have slightly skewed, or asymmetrical, mouths and feed on both sides of their prey, while older fish with more skewed mouths have a preferred attack side that matches their mouth asymmetry.

Furthermore, older fish with more skewed mouths ate more scales, which suggests choosing to be either a "righty" or a "leftie" rather than being ambidextrous, provides an evolutionary advantage.

"We observed a gradual increase in mouth asymmetry toward the preferred side of attack as the fish aged," Takeuchi addd in the study published in the journal in PLOS ONE.

By analysing the stomach contents of scale-eating fish ranging from early juveniles to adults (covering various stages of development), the research team determined the proportion of scales from the left and right sides of prey fish in over 200 cichlids.

Behavioural laterality, or left-or right-handedness, have been found in humans as well as in many animals, including, chimpanzees, toads, rats, mice, and invertebrates such as crustaceans and insects.