There are many kinds of fish, and different fish have different sleeping habits. Some fish sleep during the day and move at night, such as flounder, tiger shark, and so on, while others sleep at night, such as puffer fish, loach, and so on. There are also some non-fixed sleeping times, such as tuna and swordfish, which will sleep while swimming.
1. Hiding in the aquatic plants: For many small and medium-sized fish, they will hide in the aquatic plants when sleeping, which can play a role of cover to avoid being swallowed by other large fish. Most of the fish will be in the middle of the rocks, but also in the rest of the time to avoid natural enemies. For example, carp, crucian carp, bream and so on.
2. Hiding in the sand: Although natural rock masses such as aquatic plants and stones are very nice, for some larger fish, this hiding method does not work at all, so they find a new way to go into the sand at the bottom of the water when they sleep. Some marine fish, such as the flower sea pig fish, the thin pseudolabrus and the brocade fish, sleep in this way.
3. Encapsulated in bubbles: Some fish live near coral reefs in tropical oceans. When they sleep, they secrete a special substance on their body surface, similar to gelatine. This substance hardens when exposed to water, thus forming a bubble, which wraps the fish, but leaves a mouth for the fish to breathe while sleeping.
