Fish may seem simple at first glance, but their behaviours are often far more surprising than we give them credit for.
From complex social interactions to unexpected problem-solving skills, these aquatic animals challenge the way we think about life under the water.
This content is for general informational purposes only. Behavioural observations may vary by environment, individual fish, and species. Always consult specialists or scientific sources for detailed guidance.
1. Cleaner Wrasse
Scientists were shocked when these small tropical fish passed the mirror test, a gold standard for self-awareness previously achieved only by great apes, dolphins, and elephants. When researchers placed a colored mark on their bodies, cleaner wrasse attempted to scrub it off after seeing themselves in a mirror.
This suggests a level of cognitive sophistication completely unexpected in fish. Beyond their self-recognition abilities, these helpful little fish run underwater ‘cleaning stations’ where larger fish line up for parasite removal service, essentially operating as ocean hygienists.
2. Cichlids
Forget the myth that fish abandon their young. Cichlids display parenting behaviors rivaling those of mammals. Many species are mouthbrooders, carrying their developing eggs and newly hatched fry in their mouths for protection.
When danger approaches, parent cichlids signal their young to return to the safety of their mouths. Some species even prepare special feeding areas for their babies by fanning away debris. Their family bonds can last weeks or months, with parents teaching young to forage and recognize predators, complex social learning previously thought impossible for fish.
3. Parrotfish
Every night, parrotfish perform one of the ocean’s strangest bedtime rituals. They secrete a transparent mucus bubble that completely envelops their body, a slimy sleeping bag that masks their scent from predators while they rest.
By day, these colorful reef fish are ecological engineers. Their powerful beaks crush coral as they feed on algae, producing fine sand in the process. A single parrotfish can create over 800 pounds of white sand annually, literally building tropical beaches through their daily meals.
4. Clownfish
The real-life story of clownfish makes Finding Nemo seem ordinary by comparison. These anemone-dwelling fish live in strict hierarchies led by a dominant female, with a breeding male and several non-breeding males below her.
When the female dies, something extraordinary happens: the breeding male transforms into a female within weeks, changing both behavior and reproductive organs. The largest non-breeding male then matures into the new breeding male. This biological flexibility ensures the colony’s survival through natural succession—a sophisticated adaptation rarely seen in vertebrates.
5. Betta Fish
Male bettas craft elaborate bubble nests at the water’s surface, intricate floating structures made from saliva-coated air bubbles. These delicate architectural marvels serve as nurseries for their offspring.
After courtship, males carefully collect fertilized eggs in their mouths and place each one individually into the bubble nest. For weeks afterward, they vigilantly maintain the nest, retrieving any falling eggs or fry and repairing damaged sections. Their dedication challenges the misconception that fish lack parental instincts, bettas are among the most attentive fathers in the aquatic world.
6. Groupers
Groupers display problem-solving skills that defy our understanding of fish intelligence. These large predators have been documented using sophisticated body signals to invite moray eels on cooperative hunts.
When prey hides in reef crevices beyond the grouper’s reach, they perform a specific headshaking gesture that recruits morays to flush out hidden fish. The partners then share the meal. Remarkably, groupers will even point with their nose to indicate hiding spots to their eel partners, a form of referential communication previously thought exclusive to primates and a few birds.
7. Damselfish
Forget everything you thought about fish intelligence. Damselfish are practicing agriculture! These territorial fish cultivate private algae gardens on coral reefs, actively weeding out undesirable algae species while protecting their preferred varieties.
They aggressively chase away other herbivorous fish that might steal their crops, even attacking much larger species. Some damselfish even fertilize their gardens by urinating on them to promote growth. This sophisticated resource management represents one of the few examples of farming behavior outside of humans and social insects.
8. Pufferfish
Male pufferfish create the ocean’s most spectacular artwork, intricate geometric patterns spanning up to 2 meters across on the seafloor. Using only their fins, they meticulously craft perfect circles with elaborate radiating ridges and valleys in the sand.
Working tirelessly for days, they decorate these structures with carefully selected shells and coral fragments. The purpose? Attracting females who choose mates based on artistic skill. These sand mandalas demonstrate aesthetic sensibility and geometric precision that challenges our understanding of fish cognition and the evolutionary origins of art itself.
