Gills Just Want to Have Fun is a video from Backyard Brains that investigates the question "can fish play games just like us?" The video shows fish chasing a laser pointer around their tank, similar to the way a cat plays with a laser pointer.
I wonder, though, if the fish are "playing" or if they just think the laser pointer is a piece of food floating around. Either way, this looks like a fun experiment to try at home if you have fish.
Summary of the study:
A pending question in animal biology is whether fish are capable of complex behaviors, such as play. We investigated this by shining laser pointers of various colors into home fish tank aquariums. We tested 66 different species and found that over 80% of fish showed an inquisitive response to the moving light stimuli, with the greatest interest in red laser spots. We review the literature on fish play and discuss whether the fish responses we observed can be considered play.