The reason why fish sleep with their eyes open is that they do not have eyelids, so they cannot close their eyes at any time and can only sleep with them open. Normally, fish will stay still in the water when they sleep, or swing slightly, and when the fluctuation wakes them up, they will swim away quickly.
1. Hiding in the dark: Most freshwater fish usually hide in the dark to rest in order to ensure that they will not encounter danger when sleeping. Carp and crucian carp, for example, tend to burrow into the weeds, while mullets and snappers hide behind rocks. This can avoid the attack of natural enemies and make themselves more secure.
2, into the sand: For some benthic fish, hiding in the dark to rest, far from hiding in the sand safer. For example, the flower sea pig fish, the thin pseudolabrus and the brocade fish, these fish usually live at the bottom of the ocean, when at night, they will drill into the sand at the bottom of the water, hide to sleep and avoid being attacked.
3. Bubble wrap: Some fish wrap themselves in a jelly-like substance before going to bed. The bubbles harden when exposed to water and have a water hole to ensure they can breathe during sleep. This kind of fish mainly includes crack mouth fish and Nanyang parrotfish.
4, while sleeping while swimming: In the ocean there are some fish can not stop, they are swimming all their lives, sleep is no exception, such as sharks, tuna and mackerel, whether day or night, they have been swimming, so can not tell is awake or asleep.
