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The goldfish in your tank, the bass in the lake, and the sharks in the ocean are just a few of the 35,000 species of fish that are still alive today.
All over the world, they swim in hot springs, rivers, ponds and puddles. They glide through freshwater and saltwater. They survive in the shallows and in the darkest depths of the ocean, more than five miles down.
Salmon are iconic fish that embark on incredible migrations across oceans and fight upstream against raging currents to spawn. But when these Marathon swimmers aren’t busy migrating or reproducing, do they ever rest? Can salmon sleep?
While fish do not experience sleep exactly like humans, research shows salmon and other fish do need rest. They have cycles of intense activity and reduced activity that serve a similar restorative function as sleep in land animals.
Do Fish Sleep Like Humans?
Fish do not display the same electrical brain wave patterns or REM sleep as humans. However many fish species exhibit resting states where they reduce activity and metabolism while remaining alert to predators.
Their version of “sleep” may involve:
- Floating in place while fins make small stabilizing movements
- Wedge themselves into a secure spot like a cave or coral
- Position near the bottom or in aquatic plants
- Lower heartbeat and respiration rate
So while not the same as human sleep, fish require periods of rest to function normally. This inactive yet alert state allows them to conserve energy while monitoring for danger.
The Rest Patterns of Salmon
Research on salmon suggests they require regular rest. Their activity levels rise and fall on a 24-hour cycle aligned with light/dark.
Salmon usually sleep or rest at night, and they hunt and eat the most during the day. Their circadian rhythms regulate this cycle.
When resting, salmon may:
- Find a sheltered spot in vegetation or behind rocks
- Float in place while slowly holding position with fins
- Partially bury themselves in gravel or mud
- Remain alert to predators and changes in current
Their metabolism and heart rate decreases, and muscle activity declines. But they can quickly resume activity when needed.
Do All Salmon Species Rest the Same Way?
Salmon species can differ in their resting habits:
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Sockeye salmon tend to rest in lakes near inlet streams. They favor rocky shorelines or vegetated shallows.
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Chinook salmon rest in deeper pools, eddies, or near the bottom in rivers. They also use ocean habitats like reefs.
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Coho salmon choose small streams and headwaters. They hide under overhanging banks, trees, and in side channels.
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Pink and chum salmon rest in coastal waters, estuaries, and slow-moving sections of rivers. They prefer muddy or sandy bottoms.
So salmon select resting areas near feeding sites, while providing shelter from currents and predators.
Why Do Salmon Need Rest?
Though not precisely the same as human sleep, rest is vital for salmon health. Key benefits include:
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Conserving energy – Important when migrating long distances upstream.
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Healing and repairing muscles – Counteracts strenuous swimming.
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Strengthening immune function – Essential for combating disease.
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Processing memories – May help imprinting the homing ability to natal streams.
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Responding to injuries – Rest aids recovery from predators, fishing gear, etc.
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Managing stress – Provides respite from challenges like migration and spawning.
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Regulating metabolism – Allows fish to digest food, regulate temperature, etc.
Factors Affecting Salmon Rest
Salmon rest depends on certain conditions being met:
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Oxygen levels – Declines can make resting difficult. Warm, stagnant water impairs oxygenation.
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Water temperature – Ideal temperatures allow salmon to reduce activity and metabolism.
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Security – Sheltered, concealed spots prevent predator attacks during rest.
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Currents – Moderate flows bring food while keeping salmon in position when resting.
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Noise and light pollution – Can interfere with circadian rhythms and prevent adequate rest.
Sleep Deprivation in Salmon
Lack of rest negatively impacts salmon. Effects of sleep deprivation include:
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Impaired cognition and reactions
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Decreased immune function
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Slower growth rates
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Loss of appetite
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Increased aggression between fish
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Higher predation rates
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Reduced ability to migrate long distances
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Difficulty finding natal spawning sites
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Lower egg and sperm quality
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Higher mortality rates
Differences in Resting Behavior
Salmon exhibit variations in rest depending on life stage:
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Juveniles – Require more rest while growing and developing. They favor highly sheltered areas like overhanging vegetation.
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Adults – More active during day to build energy reserves for migration and spawning. Less total rest needed.
Farmed salmon may experience disrupted rest cycles than wild fish. Factors like artificial lighting, noise, crowding, and handling can impair their rest.
The Takeaway
Though not sleeping in the human sense, salmon clearly need periods of rest to thrive. Their resting behaviors depend on species, life stage, habitat, and environmental factors. Undisturbed resting areas are vital for maintaining healthy salmon populations. Understanding salmon sleep provides key insights that can aid conservation.
How they do it
Scientists are still learning about how fish sleep. What we do know: Their sleep is not like ours.
For one thing, people are pretty much out of it when they sleep. While a loud noise might wake you up, you’re mostly unaware of your surroundings. But fish stay aware enough to detect an approaching predator – at least most of the time.
It does appear that most fish have sleep cycles like us. Aquarium fish sleep between seven to 12 hours each day. Many fish are active during daylight and sleep at night, though for some, like numerous types of eels, rays and sharks, it’s the reverse.
Most fish don’t have eyelids, so their eyes don’t close when they sleep. That alone makes it hard to tell when they’re resting.
But if you watch fish in an aquarium, look closely. You’ll see how they stop swimming around and remain very still, sort of hovering in the water. Their gills will pump less too. For fish, that’s sleeping.
Just like you, fish need to sleep
And all of them, every last one, needs to rest. Whether you’re a human or a haddock, sleep is essential. It gives a body time to repair itself, and a brain a chance to reset and declutter.
As a marine biologist, I’ve always wondered how fish can rest. After all, in any body of water, predators are all over the place, lurking around, ready to eat them. But somehow they manage, like virtually all creatures on Earth.
Do Fish Sleep?
FAQ
What do salmon do at night?
How do you know if a fish is sleeping?
What fish sleeps the longest?
Do fish swim when they sleep?
Are salmon diurnal or nocturnal?
Salmon are mostly diurnal when temperature is high, but become more nocturnal if temperature plummets. At high latitudes, captive burbot, sculpin and brown bullhead are nocturnal in summer but become diurnal under the short photoperiod of the Arctic winter.
Is eating salmon beneficial?
Salmon is beneficial for health and is part of a healthy and balanced diet. Salmon has vitamin D, healthy fats, calcium, selenium, iodine, iron, phosphorus, magnesium, and protein.
Do fish sleep?
While fish do not sleep in the same way that land mammals sleep, most fish do rest. Research shows that fish may reduce their activity and metabolism while remaining alert to danger. Some fish float in place, some wedge themselves into a secure spot in the mud or coral, and some even locate a suitable nest.
Do Sharks sleep?
That’s sort of like sleep – at least the sharks seem less aware of what’s going on around them. There are species of shark, like the draughtsboard shark, that breathe without swimming. Scientists recently observed this shark – which is 3 feet (1 meter) long and has a flat head – sleeping on the bottom.