GoldFish– When goldfish sleep they hover in one spot to keep themselves steady. This is usually near the bottom of the tank. With their head slightly tilted downward and their eyes looking zoned out.
Guppies– Guppies sleep by lying motionless at the bottom of the tank. They can also float at the surface or rest near objects in the tank. When they float and stop swimming they sometimes appear dead but are just resting.
Bettas– Bettas are diurnal and sleep during the night like humans. Though they take the occasional day nap as we do. This they do by lying at the bottom of their tank. Though others prefer to float. For this type of fish, it’s best to get a floating log for them to sleep in.
Zebra Fish– Zebrafish sleep by lying near the bottom of the tank and dipping their tails. Or by sleep just a short distance under the surface of the water. Zebrafish have been the subject of many sleep studies and it was discovered they can suffer from insomnia. A substance called hypocretin found in mammals, helps them fall asleep. The same is available in zebrafish and when taken out it is unable to sleep or rest.
Sharks– Sharks sleep while constantly swimming. This is usually to allow proper airflow over their gills for oxygen absorption. During this time a part of their brain rests while the other remains active. Whereas some sharks don’t sleep at all..