I am Shirley Carrillo from Honest Fishers. Did you ever see your pet fish having ‘shut-eye’ moments? Hard to remember, right? But, it barely suggests that they don’t sleep. Truth is most of them do except only the way humans don’t. Well, how long does a fish sleep and why do they even do it? Still an area of researchers’ interest!
Science backs the idea that they rest, which is, in one way or another, their version of sleep. ‘Suspended Animation’ is the term that best defines the physiological state of fish as they rest. How do fish sleep then? Don’t they get insomniac ever?
Keep reading to know these and more interesting topics.
Why Do Fish Sleep and What Happens Then?
Like most living organisms, fish need to rest and have the time to restore the normal biological functions of the body.
Continued movements without a pause may cause them to become vulnerable to a reduced activity level and poor responses to dangers.
Several studies have established the fact that fish tend to a reduced level of activity and rate of metabolism at some point of the day because of the need for certain restorative functions (rest and repair) to be fulfilled.
The resting period that fish take sends signals to the brain to refresh its memory circuits and save energy. Having brains less complicated than ours, fish may not show the exact same symptoms of sleeping.
Fish have a lot simpler central nervous system than ours, which is why their brains don’t contain specific regions as humans’. Neocortex, for one, produces certain waves in our brain to make us experience variegated stages of sleep including dreaming in rapid eye movement (REM) sleep. Fish can complete the rest without these stages, REM, and dreams.
So, the question ‘how long does a fish sleep’ is more about how they behave as to the circadian rhythm (sleep-wake cycle that occurs around every 24 hours). The following signs are the clue to our conclusion that fish get sleep:
- A prolonged state of inactivity
- A typical relaxed posture
- Low respiratory rates
- A repetitive pattern of inactivity for roughly every 24 hours
- Reduced responsiveness to external stimuli
Can Fish See as They Sleep?
Probably, you’ve seen that most of them except sharks have no eyelids, which means they need not close anything. With one eye open in the restful state, their sight doesn’t get hurt. Also, the state doesn’t suspend the ability of many fish to remain alert and sense dangers.
When and How Long Does a Fish Sleep?
The answer to when and how long fish sleep may not be the same for the whooping 30,000 species. Some sleep at night while others during the day. Here’s a list that gives you some names and their usual schedules for rests:
- Nocturnal Species (the ones that stay active at night and rest during the day) include Cardinalfish, Eels, lobsters, Pinecone fish, Scorpionfish, Sea bass, shrimps, Soldierfish, Squirrelfish, starfish, etc.
- Diurnal Species (the ones that remain active during the day and rest at night) include Angelfish, Anthias, Damselfish, Butterflyfish, Parrotfish, Gobies, Hawkfish, Wrasse, Puffers, Surgeonfish, Triggerfish, etc.
- Crepuscular Species (the ones that stay active primarily during twilight, some hours of daylight and some in darkness) include Barracuda, Goatfish, Jacks, Lizardfish, etc.
- Popular Species like bass and trout become eager for feeding during early morning and late evening. Some of them may become active at night while others may choose to rest.
The duration varies from species to species. Some rely on an undisturbed period of hours at a stretch while others prefer frequent or infrequent naps followed by relatively slower bodily functions. Even some stay active for days and nights.
The case with most fish is that they’re sensitive to the environment they’re in. The water temperatures, marine settings, availability of foods, and the existence of predators and other aquatic matters heavily affect their circadian cycles.
Genetic factors are also important to note. For example, Bluehead Wrasse and Spanish Hogfish are the types that enjoy their sleep so much that they become unresponsive enough to let you pick them up without disturbing their slumber.
Zebrafish is another example of this kind with more obvious slumbering symptoms like slow heart rates, zero to no response/sensitivity to external stimuli and factors.
Questions like ‘do betta fish sleep’ or ‘do shallow water population sleep at all’ are common. Well, betta fish do have their time to rest, and that’s the night after the hectic daytime. Fish in the shallow water usually sleep except during migrations and when they’re to care for their younger ones.
Does Insomnia Mean Anything to Fish?
Most likely, yes! The results of studies on Zebrafish show that this freshwater type responds significantly to sleep deprivation. Once kept without sleep for some time, the fish were found to have a rebound effect, followed by their efforts to catch up on the lost moments.
Although it may not be the case with many species that don’t sleep, others are likely to react nearly the same way when similar experiments will be conducted.
Fish that Don’t Literally Sleep
The word ‘sleep’ meets a unique dimension when it comes to some fish that belong to pelagic species, live in open oceans, and keep swimming to maintain their gills’ ram ventilation and catch up on breathing.
Some types like blind cave fish that suffer a little stress on their brains due to the lack of the need for processing sensory information. These fish don’t usually rest to reset.
The Way Fish Rest
How and where fish choose to sleep make quite a topic of discussion for learners, fisheries experts, and anglers. Since you’re interested in learning fish ‘sleep’, the information below might interest you.
- Some keep floating either near the surface or close to the bottom.
- Part of the fish habitats includes rocks and marine algae which provide some species an excellent place to rest in.
- Some bury themselves into the soft mud or sand on the riverbed or seaboard.
- There’re fishes that do a lot of drifting by flicking their fins briskly and occasionally to keep moving.
- Some industrious kinds build their own sleeping nests (at least similar in appearance) in the sand.
- Schools of fish maintain a humanlike trend in that a few of them take care of the ‘watch for predators’ allow others to enjoy an autopilot (snoozing while going) mode for a while.
A Close Look at the Approaches of Certain Fish
Some fish adopt awe-inspiring and strange techniques to get some rest. You’ll have fun knowing about them:
- Speaking of some parrotfish, they’ve glands to secrete certain mucus that produces a cocoon to protect them from murderous parasites while blocking their scents from sneaking predators.
- There’s a symbiotic relationship between green bromis and the branching corals they sleep in. While asleep, the fish keep moving the fins quite rhythmically to channel oxygenated water to the corals to allow them to survive the lack of photosynthesis at night.
- Spotted Wolfish have no pelvic fins. So, they flip on either of their sides to stabilize the body while sleeping.
Understanding Their Habit When You Have Them as Pets
For pet fish, tanks are a common accommodation. But, how do fish sleep in a tank? They maintain an upright position resting on the bottom of the tank.
One of the most beloved species that people want to have as pets are goldfish. You might have seen one of them hovering in specific portions of the aquarium with slight movements for staying stable. Don’t worry! The fish is sleeping.
What about the ones that are not in your grasp? Do goldfish sleep in ponds? Yes, they do and with almost the same sort of physical movements as those made by them while in an aquarium.
Can You Fulfill Your Dream of Catching Fish While They’re Sleeping?
Yes, you can but with special preparations and knowledge. Remember that fish aren’t interested in biting anything for feeding as they feel like it’s time for sleep. To make your dream of catching fish come true, you may need to catch them (the ones that show up within your reach) by hands instead of the conventional fishing method.
Signs That Tell You If Fish Are Sick and Not Really Sleeping
Reduced activity or lack of energetic movements don’t always bear signs that the fish are sleeping. Sickness or other abnormalities might be the reasons, and some of these can be associated with fish ‘sleep’.
- Very sluggish moves (throughout the day) around corners, rocks, and similar places.
- Lack of stability clearly noticeable.
- Poor posture marked by imbalanced swimming across distances.
- Extended resting hours without any interruption in the life-cycle.
Frequently Asked Questions (FAQ)
These are the questions we keep receiving a lot. Answers are kept short and precise for your convenience.
01. Do Fish Swim While They Are Sleeping?
Answer: Fish are active and playful. Even while asleep, many of them can’t help moving like they’re swimming which they’re not. As mentioned earlier, green bromis will make you think likewise, but they’re only moving their fins being in a static position. Some species stay completely static and some keep moving but pretty slowly.
02. Do Fish Sleep at the Bottom of the Tank?
Answer: Yes, they do. Most species prefer the bottom of the tank over the surface areas, and this choice is part of their cognitive habits specific to their living while some might choose the areas close to the surface, especially when there’s a lack of oxygen or light.
03. How Many Hours Do a Fish Sleep?
Answer: Unfortunately, no studies have brought us any definitive or concluding result showing exactly how many hours fish sleep. However, most species remain in slumber for at least a few (2-3) hours a day with many others being in that state for extra hours, which in fact depend on the factors mentioned above.
04. How Much Light Do Tropical Fish Need?
Answer: Depending on the live plants, ambient lighting, algae level, and the presence of other species in the surroundings where tropical fish are living, they need up to 11-12 hours of lighting. Common tropical fish are Corys, Catfish, Danios, Guppies, Gouramis, Loaches, Raspboras, Platies, Mollies, Plecos, Tetras, Swordtails, etc.
So, how do fish sleep? You already know it! But, the answer to the question ‘how long does a fish sleep’ is rather vague. It can be several hours a day or brief, recurrent naps, or even only a few moments for some species.
However, fish just like other animals and living creatures need it for survival, no matter the way or for how long they rest.