There are several species of fish that are observed really sleeping. So the answer for “DO FISH SLEEP” is YES without any doubts.
The researchers still struggle to define what sleep really is, and why so many species need to sleep. A commonly used definition for sleep is that; animals are accepted as sleeping, if they regularly rest in a certain position and simultaneously reacts less to sensory stimuli, such as light, sound, electricity and pressure.
In the light of this definition, the researchers found examples of sleepers in virtually all animal groups – even in bees and wasps.
Biologists knowledge of the sleep habits of the fish are, however, quite limited – for example, they are not sure if any fish species need to sleep.
How Do Fish Sleep? Which Fish Species are Observed Sleeping?
The zebrafish is showing clear signs of sleep
The Zebra Fish, show clear signs of sleeping and is frequently used in sleep research. Both larvae and adult Zebra Fish goes into sleep states; where they show less reaction to sensory inputs. When larvae are sleeping, keep the head down while the adult fish sleep revealed opposite behavior.
When it’s bedtime, the most dormant species just go towards the bottom without any other special preparations.
Blind fish do not sleep
Fish that live in dark caves or born blind (eg the Mexican Typhliasina pearsei ), shows no sign of sleep behavior.
Scientists believe that these species do not need sleep. They are not stimulated visually, and therefore their brains doesn’t react on those kind of stimulus.
Shoal Fish have similarly less need for sleep, Because they just concentrate on following the closest fish in the shoal and therefore use their sense of vision significantly smaller than fish that do not live in shoals.
Parrot fish do sleep in a slime balloon
Parrot fish has an exceptional talent. Parrot fish lies down to sleep in the coral reef, secrete a mucous bag through the mouth. After half an hour the slime bag encloses the whole body, and parrot fish settles in its secure balloon. This Mucus balloon probably hides its smell to predators and thus provides Parrot Fish with a safe heaven.