I know that birds, humans and various other animals sleep, but do fish sleep? What other animals do not sleep?

All living creature must have some form of rest for the restorative value and the purpose of gaining energy.

However, sleep means different things to different forms of animal life. Most animals have some daily pattern of rest and activity. This applies to fish as well. Some fish keep very still, experiencing a quiet period (quiescence) that you might call sleep. Scuba divers often handle reef fish in the middle of the night without startling them and can even lift some species out of the water before they awaken. Tropical freshwater fish in home aquaria appear to be resting immediately after turning the lights on in a room that has been darkened for several hours. Unfortunately, fish have no eyelids so it is difficult to tell whether they are asleep or not.

Being asleep can mean different things to different fish. Some fish undergo a yearly sleep cycle. They hibernate and their metabolic rate slows down. Some fish practice estivation, a state of torpor or dormancy in which they spend time during hot, dry periods to protect themselves from dehydration and some fish are motionless in the water during the night.

They sleep, but not completely. They go through stages1, 2 and 3, but not through four. It's like sleep walking, but in this case swimming. Since fish don't go through stage 4 they are not able to go through the process of R.E.M(Rapid eye movement)because they have no eye lids, so scientists think fish don't have dreams. Hope that helps!