While fish do not sleep in the same way that land mammals sleep, most fish do rest. Research shows that fish may reduce their activity and metabolism while remaining alert to danger. Some fish float in place, some wedge themselves into a secure spot in the mud or coral, and some even locate a suitable nest.
It's pretty easy to tell when fish are sleeping: they lie motionless, often at the bottom or near the surface of the water. They are slow to respond to things going on around them, or may not respond at all (see some sleeping catfish here). If you watch their gills, you'll notice they're breathing very slowly.
This is supported by studies on several species of blind fishes that live in caves. These sightless fishes do not sleep.
Surface fish usually stay active during the day and sleep during the nighttime, too. Their eyesight makes it easier to see food during the daytime, and they sleep at night because they can't see well then.
Many species of bony fishes, sharks, and rays breathe by opening and closing their mouths to push water over their gills. This process enables them to float still for a long time, breathing while they sleep.
How Long Do Fish Sleep? Aquarium fish sleep for an average of eight to 12 hours. Because sleep time is driven by light, plan to keep the aquarium lights on for eight to 12 hours, allowing for 12 to 16 hours of darkness.
Fish species can also be diurnal, which means they generally sleep at night, or nocturnal, which means they are generally active at night. For example, nocturnal sharks rest during the day and then swim and look for food at night.
As well as getting water through osmosis, saltwater fish need to purposefully drink water in order to get enough into their systems. Where their freshwater counterparts direct all of the water that comes into their mouths out through their gills, saltwater fish direct some into their digestive tract.
Fish living in the deep sea manage to navigate in complete darkness. It's not strictly 'seeing' but fish have rows of pressure-sensitive organs running down each side of their body called the lateral line, which allows them to sense nearby animals from the pressure changes in the water.
Nerves, brain structure, brain chemistry and behaviour – all evidence indicates that, to varying degrees, fish can feel pain, fear and psychological stress.
Fish have kidneys which produce urine containing ammonium, phosphorus, urea, and nitrous waste. The expelled urine encourages plant growth on coral reefs; downstream benefits also include increased fertilization of algae and seagrass, which in turn provides food for the fish.
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.
But the bullfrog, Lithobates catesbeianus show the same reaction in both situations. This indicates that bullfrogs do not sleep. Lithobates catesbeianus is an animal that cannot sleep.
Each fish gets food especially for them – some eat plankton and fruit flies, others eat seeds and vegetables; some fish hunt for their food, others forage for it. Once they've eaten, fish spend their days guarding their homes, and at this time of year, breeding season, they spend lots of time competing for mates.
Can your pet fish recognize your face? A new study says, Yes, it probably can. Researchers studying archerfish found the fish can tell a familiar human face from dozens of new faces with surprising accuracy.
Yes, fish can hear you talk!
Sounds that are created above water typically do not carry enough force to penetrate the surface tension of the water, so talking on the boat or loud noise may not affect fish as much as your fellow anglers may want you to think. Your voice is unlikely to spook or scare fish away.
Overall, green light attracts the most fish. Green has a high lumen output of 130 per LED alongside a 520 nm wavelength. Shrimp and insects have both of these wavelengths in their color vision alongside green light receptors around 530 um.
Bullfrogs… No rest for the Bullfrog. The bullfrog was chosen as an animal that doesn't sleep because when tested for responsiveness by being shocked, it had the same reaction whether awake or resting.
Sharks can sleep, and often opt to keep their eyes open while they do, according to new research published in Biology Letters. Because some sharks must swim constantly to keep oxygen-rich water flowing over their gills, it has long been rumored that they don't snooze at all.
Fish typically have quite small brains relative to body size compared with other vertebrates, typically one-fifteenth the brain mass of a similarly sized bird or mammal.
Surprisingly, science has found that fish are capable of recognizing their owner's face, even if the owner is standing by the tank with other people. Fish can develop an association between something they like, being fed, with the person who feeds them.
Most fish are slightly denser than water, so sink immediately after death. However, like a drowned human, they become more buoyant over time as bacterial decomposition produces gases inside the body. Usually, enough gas builds up in body cavities to make the corpse float, like an inflated balloon.
It is possible to wake a sleeping fish. Enough light or noise will eventually get them to wake up.
Bright colors will help alert fish to your presence, and often spook them.