On the whole, the answer is yes, fish do sleep. However, their sleeping habits differ significantly from those of humans and other land animals.
When fish sleep, most enter a restful state where they remain still, have lower metabolic rates, reduced breathing, and less brain activity.
It’s pretty easy to tell when fish are sleeping: they lie motionless, often at the bottom or near the surface of the water. If you watch their gills, you’ll notice they’re breathing very slowly.
Fish Sleeping Patterns and Behaviors
Fish continue to swim and move around even when they are sleeping. Many fish go into a state of rest, become less active, reduce their metabolism, and slow down their body functions.
Fish like us are diurnal, meaning they move around in the daytime and rest at night. 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.
In contrast, nocturnal fish stay active throughout the day but hide out in the dark at night to avoid predators.
Do Fish Swim While Sleeping?
Unihemispheric sleep allows a fish to put one half of their brain to sleep at a time, while the other half stays active, allowing the fish to keep swimming, albeit more slowly than when they are awake.
Some fish like Tetras and Guppies will find a place to hide and sleep at night as an instinct to avoid becoming prey. It’s a good idea to provide plants and aquarium decorations for these small species of fish to hide.
In conclusion, while fish do not sleep in the same way humans do, they do go through periods of rest and relaxation. Certain behavioral changes and physical signs can indicate when fish are in a resting state.