The answer to this question is actually “yes”. Although fish do not close their eyes and lie down just like human does, what they will do is that, the fish will just stay idle and rest quietly at the bottom of the tank or maintain the position right beneath the water surface. That’s why it is very important to have a day and night cycle in your aquarium and ensure that the water movement is not vigorously or else the fish won’t be able to keep still and maintain the same position in the water while they sleep. Equip your fish tank lighting with a timer so that it will automatically turned off during nighttime to allow them to take a rest.
Ensuring that your fish is getting enough sleep is very important because without sufficient resting time, you will notice that the fish will start to lose coloration and they will not develop good appetite for food during feeding. Some fish may even become stunted as well if the condition persists. In fact, past research reported in PLoS Biology Journals even suggested that fish can ever suffer sleepless nights that will eventually disrupt their health.