How long do fish have to 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.
How do fish sleep with their eyes open?
The short answer here is yes, and the short explanation for why is that fish don’t have eyelids. They physically cannot close their eyes, whether they’re sleeping or not. In the context of their environment, this makes sense.
How do fish sleep on their side?
Sleeping fish remain stationary but upright; they do not turn sideways or upside down. A fish that is leaning, is upside down, or lying on the bottom isn’t sleeping but is likely sick.