If you’ve ever owned a pet goldfish, chances are you’ve entertained the curious notion of whether fish tuck themselves in at night. You might have pondered questions like, “What’s the aquatic equivalent of a bed?”, “Can fish close their eyes?”, and “Do fish actually need to rest?”.
A particularly imaginative mind might anthropomorphize a goldfish, giving it bedtime rituals akin to our own. Though goldfish don’t necessarily need a soft bed of pebbles, complete darkness, and the comfort of natural silence for rest, providing these luxuries definitely won’t hurt!
Extremely important for physical recovery, mental processes, and overall health, sleep is something that almost all animals need. The way humans sleep, however, is not necessarily how a fish would sleep. While humans need around 6 – 8 hours of preferably nocturnal rest, fish actually need more hours within a state of “sleep-like rest”. Though this state is regulated by the circadian rhythm in fish, just as it is in land mammals, it does not exactly equate to our dream state wherein some sensory inputs are largely ignored.
A Sleep-Like State of Rest
While we can be certain that goldfish do need to routinely shift between periods of wakefulness and rest, it is still uncertain if they enter the same phases of sleep as land mammals. Recent research has suggested that they do to some extent, but this does not mean that they conjure up dreams as they enter a state of subconsciousness. Sleep, as a whole, has been very challenging to quantify or even identify in fish; their lack of eyelids certainly doesn’t help!
That being said, it’s well known that all aquarium fish, including goldfish, need to rest in order to survive, undergo developmental stages of growth, and function normally. A complex combination of neuronal signatures, with changes in brain wave activity, hormonal activity, heart rate, muscle usage, and eye movement, affect how fish recover from an active day during their peak growth period. As far as researchers can tell, all vertebrates, which operate using a complex system of neural circuits, need to doze off every now and then.
When goldfish enter their own form of “sleep”, they go through phases of slow-wave sleep and something similar to REM sleep. The former is associated with a decrease in brain activity, while the latter may be manifested by muscle inactivity and peaks in brain wave action. Melatonin, a hormone produced by the goldfish’s pineal organ, is instrumental in regulating their rhythmic need for rest.
Clear Signs Your Fish Is “Sleeping”
If you’re new to caring for fish, it may be easy to confuse your goldfish’s resting phase with symptoms of sickness or stress. A “sleeping” goldfish tends to stay close to the bottom of the tank. It may remain in this part of the tank for hours, usually making minimal and calm movements to hover just above the tank’s floor or bottom substrates. Of course, as it does not have eyelids, its eyes remain wide open throughout this entire period of rest.
A healthy goldfish will usually have an upright body, though its head may be slightly angled downward, while resting. It will not lie on its back or side, as many larger mammals would. In contrast, a sick or stressed goldfish may float in a lopsided manner or may appear prostrate, with its whole body in contact with the tank or pond bottom. It may display other clear signs of stress, such as refusal of food, an inability to move normally after being prodded, marked discoloration, and the development of reddish blotches on some parts of its body and fins.
How Can I Help My Goldfish Rest?
Like us, goldfish appreciate dimmer lights and some peace and quiet as they rest. They will typically “sleep” at night, once the pond or tank lights have been switched off, and enter their active phase as soon as their environment is brightly lit. In indoor locations, regularly timed hours of light and darkness should help them maintain their circadian rhythm.
To maintain a healthy “sleep” pattern, make sure that your tank lights are not switched on for more than 12 hours per day. It may be tempting to leave the lights on through the night, especially for ornamental ponds or aquariums, but this is not advisable for prolonged durations. You’ll find that goldfish will search for dimmer spots, perhaps beneath vegetation or in a makeshift cave, in brightly lit tanks or ponds. Ideally, they should be exposed to more than 6 hours of darkness per day.
Remove sources of both noise and physical disturbances. Just as sudden bright lights (leading to “light shock” in fish) and loud sounds can startle and rudely awaken a person up at night, they can cause your fish to panic and remain on high alert. Objects that slam onto the tank, causing vibrations that force fish awake, may even cause them to attempt to jump out of the water.
Rest Deprivation in Fish
Sleep deprivation or insomnia has been shown to negatively affect the cognitive abilities of fish. It is also likely to affect their immunity from diseases as well as their rate of recovery. This occurs when fish generally feel unsafe in their tank, pond, or wild environment and feel as though they need to remain awake to survive. This also occurs when they are not provided with conditions that are conducive to maintaining a healthy circadian rhythm.
To recover from the effects of a brief period of sleep deprivation, fish are likely to undergo what researchers have termed a “sleep rebound”. This simply means that they catch up on the lost hours by spending more time sleeping or entering many “microsleep” states. Based on research that has focused on zebrafish (Danio rerio), an inability to recover from lack of sleep can impair a fish’s attention span, responsiveness to external stimuli, and locomotor skills.
We can assume that these same effects extend to goldfish and other ornamental pond and tank species. Presumably, repeated and prolonged disturbances to their resting patterns can eventually lead to long-term and serious illnesses. Unsurprisingly, the effects of sleep deprivation on fish have been tapped as a source of clues to the physiological effects of insomnia on mammals, including dogs and humans.
Do Goldfish “Sleep” or Hibernate in Winter?
Goldfish, like koi and many other coldwater ornamental fish, enter a state of inactivity during cool winters. Though this is sometimes referred to as “hibernation”, it is not identical to mammalian hibernation. The proper term for their state of prolonged winter rest is “torpor”. This state, which can last for weeks, is a means to conserve energy in markedly cold temperatures. Temperatures below 50˚F (10˚C) can cause their metabolism to slow down significantly.
In torpor, goldfish usually stay in the warm, bottom zone of the water column. They’ll appear to be lethargic or fast asleep, moving only to forage for minimal food or to escape potential predators. Every time they shift to a period of activity, they emerge from a brief state of torpor. They’ll shift to shorter, regularized periods of rhythmic “sleep” once temperatures stabilize in spring.
