Fish Can Be Right-Handed Or Left-Handed, Study Shows

From the day you first pick up a pencil to write or a baseball bat to swing, you are labeled either a "righty" or a "lefty." But are certain distinctions made in fish, too? 

In the latest study from Nagoya University, Japan, researchers investigate the development of behavioral laterality, or left -- or right-handedness, in cichlid fishes. They chose to focus on a scale-eating cichlid from Africa's Lake Tanganyika, Perissodus microlepis, according to a news release. 

Previous studies have found behavioral laterality exists in many animals, including humans, chimpanzees, toads, rats, mice, and invertebrates such as crustaceans and insects. In terms of the scale-eating cichilds, researchers 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. (Scroll to read more...)

"This is truly an important study because it allowed us to observe mouth direction development with age and the relationship between behavioral laterality and mouth asymmetry in these fish," lead author Yuichi Takeuchi explained in the release. "We can now also address the question of which came first, scale-eating or mouth asymmetry."

By examining the stomach contents of nearly 200 scale-eating cichild fish ranging from early juveniles to adults -- covering various stages of development -- researchers were able to identify the age at which the fish transition from eating scales from both sides of their prey to preferentially attacking one side. 

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 added. "This is exciting because it is the first documented evidence through field work on the development of behavioral laterality."

Their study was recently published in the journal PLOS ONE. 

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