We know that the nature of a fish’s tank will have an influence on its brain and behaviour. When young trout are reared in a boring, featureless tank they develop a smaller cerebellum (part of the brain that regulates movement) than trout that are given rocks and plants to explore. Cod reared in similarly enriched tanks become better at learning how to catch prey, and also recover quicker from stress after a simulated predator attack.
But whether fish actually feel bored in a way we can relate to is harder to work out. Fish-keepers sometimes see their pets ‘glass surfing’ – swimming repeatedly up and down the glass of the tank. This could be the aquatic equivalent of the pacing of a captive tiger that’s bored from a lack of stimulation. But the fish could also be stressed from an overcrowded or unfamiliar tank.