Fish do play with each other, and they also play alone. While the science of fish play is still young compared to research on mammals or birds, a growing body of evidence shows that multiple fish species engage in repeated, voluntary behaviors that serve no immediate survival purpose, which is the basic definition of play. These behaviors range from chasing tankmates and riding water currents together to batting objects around an aquarium.
What Counts as Play in Fish
Play is tricky to define in any animal, but researchers generally look for a few hallmarks: the behavior is voluntary, repeated, doesn’t serve an obvious survival function like feeding or escaping predators, and happens when the animal is relaxed and well-fed. Fish meet these criteria more often than most people expect. The challenge is distinguishing genuine play from territorial aggression, foraging, or mating displays, which is why scientists were slow to study it in fish at all.
That skepticism has shifted. Documented play in fish now falls into three broad categories: social play (interacting with other fish), object play (manipulating things in the environment), and locomotor play (moving through water in exaggerated or repetitive ways for no clear reason). Some species show all three.
Social Play Between Fish
Social play is the hardest type to confirm in fish because it looks a lot like aggression or courtship. But certain behaviors stand out. Cichlids, for instance, have been observed chasing and nudging each other in patterns that don’t match territorial defense or breeding. The interactions are gentle, reciprocal, and often repeated between the same individuals, more like roughhousing than fighting.
Anemonefish and damselfish living in the same host anemone have been observed lunging together at novel stimuli, like a red laser dot circled around their anemone by researchers off the coast of French Polynesia. These fish weren’t feeding or defending territory. They were responding to something novel, and doing it alongside their neighbors. Whether this qualifies as cooperative social play or just parallel curiosity is still debated, but the behavior was voluntary, repeated, and served no survival function.
Aquarium hobbyists regularly report fish playing together in less formal settings. Betta fish owners describe their fish repeatedly swimming into filter currents and getting pushed across the tank, then circling back to do it again. In mixed-species tanks, white cloud minnows have been observed “teaching” pygmy corydoras to surf the bubbles from sponge filters, with both species eventually riding the current side by side.
Object Play: Batting, Pushing, and Chasing Things
Object play is where the evidence is strongest and most surprising. Elephant fish, a family known for having unusually large brains relative to body size, have been observed pushing twigs around their aquariums, balancing objects on their snouts, and manipulating plastic balls, all while well-fed and under no environmental pressure. This isn’t foraging behavior. The fish return to the objects repeatedly and interact with them in varied ways.
White-spotted African cichlids were the subject of a landmark 2015 study that documented three individuals playing with self-righting thermometers. The fish repeatedly knocked the thermometers down and pushed them around their tanks. The thermometers would pop back upright, and the cichlids would knock them over again, sometimes dozens of times. Rough silversides have been seen head-butting and charging a nylon line, and a sterlet (a type of sturgeon) was documented vigorously pushing and pulling objects in its tank with no food reward involved.
Laser pointer experiments have expanded the list further. When researchers shone a red laser dot near aquarium fish, several species chased it enthusiastically for five seconds or more, including clownfish, giant danios, rainbow sharks, royal grammas, and tiger barbs across five color varieties. About 23% of the 66 fish tested showed this high level of engagement. Like a cat chasing a laser, these fish were pursuing something they couldn’t catch or eat, purely for the interaction itself.
Riding Currents and Surfing Bubbles
Locomotor play, the fish equivalent of a dog zooming around a yard, shows up most visibly in aquariums with water flow. Betta fish are frequent performers. Owners describe them swimming deliberately into the waterfall from a filter, getting pushed down and forward several inches, then looping back to the top and doing it again. Some bettas swim into the jet output from a filter and ride the current nearly all the way around the tank before returning to start over.
This isn’t accidental. The fish actively seek out the current, position themselves in it, and repeat the circuit. It looks remarkably like a child going down a water slide. The behavior happens when the fish are otherwise calm and well-fed, and they choose to stop whenever they want. It fits every standard criterion for play.
Why Fish Brains Support Play
Fish have a reward system in their brains that works much like the one in mammals. Two regions in the fish forebrain process rewards and drive motivation using dopamine, the same chemical messenger that makes pleasurable activities feel good in humans. This dopamine pathway handles everything from learning where food is to evaluating social partners and making context-dependent decisions.
Research on cleaner wrasses showed that stimulating one type of dopamine receptor significantly improved the fish’s ability to learn reward-based tasks. When these fish encountered an unexpected reward, their brains kicked into goal-directed learning, speeding up how quickly they figured out new patterns. This same reward circuitry is what makes play feel rewarding. A fish riding a current or batting a thermometer is likely getting a small dopamine hit each time, reinforcing the behavior just as it would in a dog fetching a ball.
The existence of this reward pathway helps explain why play appears across such different fish species. It isn’t a quirk of one unusual lineage. The underlying brain hardware is shared across bony fish as a group.
Why Play Evolved in Fish
The evolutionary purpose of play remains one of the more debated questions in animal behavior, and fish are no exception. Several theories overlap. The simplest is that play burns excess metabolic energy in animals that are safe, well-fed, and have nothing urgent to do. A more sophisticated view is that play helps young or captive animals develop flexible motor skills and problem-solving abilities they might need later, essentially rehearsing for unpredictable situations without the stakes of real danger.
Some researchers break play into levels of complexity. At the most basic level, play provides behavioral variety that natural selection can work on over generations. At a middle level, it helps individual animals develop physical and psychological abilities during their lifetimes. At its most advanced, play builds flexible, creative skill sets that help animals cope with unexpected challenges and changing environments. Fish likely operate mostly at the first two levels, though species like elephant fish, with their large brains and complex object manipulation, may push into the third.
Encouraging Play in Pet Fish
If you keep fish at home, you can encourage playful behavior by providing novelty and variety. Professional aquarists at facilities like the Seattle Aquarium use several strategies that work in home tanks too.
- Rearrange the environment. Moving rocks, plants, or decorations mimics the ever-changing conditions of natural habitats and gives fish new spaces to explore.
- Adjust water flow. Changing the position or strength of a filter output gives fish new currents to interact with, which is especially stimulating for species like bettas and white cloud minnows that enjoy riding currents.
- Add safe objects. Floating ping-pong balls, aquarium-safe toys, or even a self-righting object can give curious species something to investigate and push around.
- Vary feeding methods. Frozen food in ice cubes, lettuce clipped to the glass, or food scattered across the tank instead of dropped in one spot encourages natural foraging behaviors that overlap with play.
- Try a laser pointer. A brief session with a red laser dot (kept short to avoid stress) can engage species like clownfish, tiger barbs, and danios. Not all individuals respond, but about one in four fish shows strong interest.
The key principle is novelty. Fish in unchanging environments with predictable feeding routines have little reason to explore or interact. Fish in environments that shift regularly are more active, more curious, and more likely to display the kinds of voluntary, repeated behaviors that qualify as play.