Fish just want to have fun - scientists studying a group of male Tropheus have documented play in cichlids.
"Play is repeated behaviour that is incompletely functional in the context or at the age in which it is performed and is initiated voluntarily when the animal or person is in a relaxed or low-stress setting," said Gordon Burghardt of the University of Tennessee.
He and his colleagues Vladimir Dinets and James Murphy of the Smithsonian National Zoological Park in Washington, DC, are the first to document play with objects in a cichlid fish species. There are hundreds of species of cichlid, but the behaviour of the species they studied appears unique.
The three male Tropheus duboisi were studied and filmed individually over the course of two years. Researchers observed the fish repeatedly striking a bottom-weighted thermometer. The presence or absence of food, or other fish within the aquarium or visible in an adjacent aquarium, had no effect on their behaviour. The thermometer-attacking behaviour satisfies Burghardt’s criteria for play.
The quick righting response of the bottom-weighted thermometer seemed the primary stimulus factor that maintained the behaviour, according to Burghardt. "We have observed octopus doing this with balls by pulling them underwater and watching them pop back up again," he says. "This reactive feature is common in toys used for children and companion animals."
Burghardt says his research illustrates how play is embedded in species’ biology, including in the brain. Play, like much of animals’ psychology including emotions, motivations, perceptions and intellect, is part of their evolutionary history and not just random, meaningless behaviour.
"Play is an integral part of life and may make a life worth living," said Burghardt.
The research is published in the journal Ethology.