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Why Do Fish Lay At The Bottom Of The Tank? Reasons & Solutions

why do fish lay at the bottom of the tank

Noticed your fish suddenly displaying some unusual behavior? Want to know if there’s a cause for concern? Why do fish lay at the bottom of the tank? How can you tell if it’s normal fish behavior or if you need to intervene?

Fish laying at the bottom of the tank is normal behavior if it happens routinely. If this behavior is new and other signs of distress/disease accompany it, you need to investigate the cause.

There are plenty of circumstances where it’s normal for aquarium fish to lay near the bottom of the tank, especially when resting.

This is common in particularly bare setups. If there are little to no hiding spots, the bottom of the tank might be the safest spot for your fish to go to take a break.

If one or more fish suddenly start laying ONLY at the bottom of the tank, you’ll need to monitor them closely. Signs like a lack of appetite, labored breathing, clumsy swimming, or loss of buoyancy control are red flags. In this case, it’s best to quarantine the fish immediately and address the root problem.

One of the best things about the fishkeeping hobby is watching an endless loop of playful fish swimming. It’s only natural to be a bit concerned when your pet fish choose to lay motionless at the bottom of the tank.

Making the distinction between what is normal fish behavior and what is not will help you enjoy your fish more in the long run.

We’ll also get into what red flags to look for if laying at the bottom of the tank is a new behavior.

Normal Reasons Why Fish Lay At The Bottom Of The Tank

fish at bottom of tank not moving
Cory catfish (Corydoras acutus)

There are several normal, non-concerning reasons why fish may lay at the bottom of the aquarium:

Bottom dwellers

Fish that spend the majority of their active hours near the bottom of the tank might just be naturally inclined to do so.

Some loaches, cory catfish, or plecos are perfect examples of content bottom dwellers that you’ll see roaming the lower levels of your aquarium.

If you have a planted tank with many low-growing plants, fish might prefer hanging out near the bottom to explore the mini aquatic jungle.

Bottom feeders

Bottom dwellers are often also bottom feeders. They prefer roaming at the bottom of the tank because that’s where they also eat. They will either gulp fish food as it sinks to the bottom or scavenge for leftovers among the gravel.

Resting fish

It’s perfectly normal for fish to rest and sleep while lying at the bottom of the tank.

Healthy fish will do this between sessions of active and energetic sessions of swimming.

You should keep the lights on your aquarium on a diurnal schedule (8-10 hours of light per day) to encourage your pet fish to rest.

Providing them with cave-live decorations and live plants is also a good way to keep fish stress levels low. Laying at the bottom of the tank to rest can be stressful, as the fish will feel exposed and vulnerable.

Older fish

Aquarium fish have relatively short lifespans, the most common species averaging around 3-5 years.

As they age, your pet fish might tend to rest near the bottom of the tank more often than before.

In between periods of time when the fish are active, short breaks or resting shouldn’t be a cause for concern.

Newcomers

When first introducing new fish to a tank, they will instinctively look for places to hide. If your aquascape lacks refuge areas, newcomers will resort to laying at the bottom of the tank.

With compatible tank mates, healthy fish will get over their fear soon, and start exploring their new home. So, if this behavior is temporary, there’s no reason to worry.

Concerning Reasons Why Fish Lay At The Bottom Of The Tank

fish staying at the bottom of the tank
Kuhli loach (Pangio kuhlii)

There are other, more concerning reasons why a fish may lay at the bottom of the aquarium:

Hiding at the bottom of the tank

Red flags

You notice a fish choosing to lay at the bottom of the tank, even though they’re typically mid-level swimmers or surface feeders.

Monitor the fish, and see what happens whenever it tries to swim away from the bottom. If it’s getting harassed by a bully or getting nipped at, there’s a tank mate incompatibility issue.

This can also happen if:

  • your tank is not large enough;
  • the aquarium is overstocked with fish;
  • you have too many fish sharing the same swimming level in a tank.

Solutions

  • Add more hiding spots (decorations, live aquarium plants) to give vulnerable fish more refuge areas.
  • Identify the bully/harasser, and remove it if the harassment continues past the “asserting dominance” phase. Repeat offenders can seriously injure their tank mates if you take no action.
  • Get a mix of bottom dwellers, mid-to-top swimmers, and surface feeders to divide the space inside your aquarium.
  • Check to see if your tank is overstocked, using AqAdvisor. If it is overcrowded, consider getting a bigger tank.
  • Get an additional tank for the distressed fish lying at the bottom of the tank. If they’re simply incompatible with the other fish in your community tank, this might be the only solution.

Displaying territorial behavior at the bottom level

Red flags

In the opposite scenario to the one listed above, a territorial fish might lay at the bottom of the tank to claim it as its territory. This doesn’t often happen in an established tank that’s aquascaped to accommodate this normal fish behavior.

Noticing fights for dominance and aggressive behavior happening mostly at the bottom level of the tank? A struggle for territory might be the root cause of this behavior. 

Solutions

  • Make sure your tank setup is large enough to allow territorial fish to claim a territory within it.
    In a tank that’s too small, aggression is bound to happen, as fish can’t avoid staying out of each other’s space.
  • Aquascape your aquarium to visually divide it into sections. A few tall background, or midground, live plants, can do wonders in getting a territorial fish off of the bottom of the tank.
  • Check for tank mate compatibility before introducing any new fish going forward. And if you do have bottom dwellers that have to share their space with a territorial fish, make sure they have plenty of refuge spots.

Water temperature is either too low or too high

Red flags

A fish, or more, laying at the bottom of the tank is exponentially more concerning when coupled with:

  • labored breathing and obvious erratic gill movement;
  • change in appetite, sometimes eating more, can lead to overeating troubles (constipation, bloating, etc.).

When the water temperature inside your aquarium drops too low, your fish might lay motionless at the bottom of the tank to conserve energy.

On the opposite spectrum, if the water temperature rises dangerously high, fish will stay on the bottom because that’s where oxygen levels will be higher.

A sudden increase in water temperature can also trigger your fish’s metabolism to accelerate. They will eat more and produce more waste in the process.

Too high of a water temperature, paired with insufficient aeration (water circulation), is a recipe for disaster! So are frequent and drastic changes in water temperature.

Solutions

  • Get an aquarium heater with a digital controller to keep the water temperature inside your tank stable. Make sure the heater has the appropriate wattage for the capacity of your particular setup.
  • Research the optimal water temperature range you should be aiming for, depending on the fish species you’re keeping.
  • Avoid keeping tropical fish in the same tank as coldwater fish because their water temperature needs are complete opposites.

Significant drop in water quality and unstable water parameters

Red flags

Fluctuating water parameters go hand in hand with overall poor water quality inside a fish tank.

The biggest red flags, in this case, are sudden changes in your fish’s behavior. These changes will more often than not be visible in most of the tank’s inhabitants.

Hardier fish species will just lay at the bottom of the tank when the water quality drops. But more sensitive fish will be at high risk for diseases. Stress-induced drops in fish immunity can lead to:

  • Fungal infections;
  • Bacterial infections;
  • Parasite infestations;
  • Self-inflicted injuries from erratic swimming.

Solutions

  • Research the optimal water parameter ranges for the fish species you’re keeping.
  • Use aquarium test kits to monitor pH levels, Ammonia, Nitrite, and Nitrate concentrations.
  • Aim to keep water parameters (pH, water hardness, salinity, etc.) at a constant level, rather than chasing the perfect value on a test kit.
  • Fluctuations are more dangerous and stressful for fish than having a pH level that’s at the bottom of the recommended range.

Sometimes you put together the pieces to the puzzle too late, even as a seasoned aquarist.

If your fish are not only lying at the bottom of the tank but also displaying other concerning symptoms, quarantine them. If all your fish show obvious signs of distress, there might be a disease running rampant inside your fish tank.

Diseases That Can Cause Fish To Lay At The Bottom Of The Tank

Corydoras bottom dweller
Armored catfish (Corydoras aeneus)

Stress-inducing tank conditions (off-balance water chemistry, poor water quality, etc.) can trigger a disease outbreak among aquarium fish.

As a precaution, always quarantine diseased fish in a “hospital tank” when monitoring their condition. A quarantine tank also makes it easier for you to medicate the fish in question.

Learn how to identify the symptoms of the most common diseases that can cause fish to lay at the bottom of the tank.

Noticing this first concerning sign can help you treat a disease in its more manageable early stage.

Ammonia poisoning

Ammonia poisoning is one of the deadliest conditions that can be easily overlooked when fish are lying at the bottom of the tank.

You should test the water to determine ammonia/nitrite levels in the aquarium. If more than one fish is showing a sudden change in behavior, ammonia poisoning is highly likely.

Ammonia poisoning symptoms also include:

  • A loss of appetite;
  • Labored breathing;
  • Fish gather in areas of the tank with richer oxygen levels (at the bottom of the tank or near the filter’s output).

Causes

  • Overcrowding;
  • Overfeeding;
  • Adding too many fish in an uncycled tank without using a bacteria starter;
  • Deep-cleaning a tank and disturbing the aquarium’s established culture of good bacteria.

Treatment

  • Use aquarium test kits to determine the ammonia level inside your tank. The only safe ammonia level is zero, so any other reading should be a red flag.
  • Do a 25-50% water change to dilute the concentration of ammonia as quickly as possible. Use dechlorinated water or tap water that’s been sitting for at least 48 hours.
  • Avoid feeding your fish more than the bare minimum until the biological balance gets
  • Cycle your tank if it’s a new setup.
  • Monitor ammonia levels weekly.

Swim bladder infection

If your fish laying at the bottom of the tank is accompanied by a loss of buoyancy control, a swim bladder infection might be the reason.

A fish’s swim bladder is a gas-filled organ that makes it buoyant. When healthy, the swim bladder allows the fish to swim and float at all levels of the aquarium.

When fish are suffering from a swim bladder infection, they will either get stuck floating only near the water’s surface or sink to the bottom of the tank.

You’ll also notice the affected fish struggle to float upside.

Causes

  • Dangerously low water quality;
  • Overeating;
  • Constipation;
  • Swim bladder infection can sometimes be a secondary infection to other bacterial infections;
  • Develops as a secondary condition to kidney malfunctions, impacted eggs in females, etc.

Treatment

  • Check water parameters, and address the root causes of poor water quality.
  • Stop feeding your fish for 24-48 hours. Most fish will do just fine with a brief fasting period.
  • If constipation is the trigger of the swim bladder infection, feed fish more fiber.
  • If you suspect a bacterial infection, give your fish a salt bath (1 Tbsp salt to 3 gallons of water) using aquarium salts.
  • Use an antibacterial solution that binds to fish food to treat the swim bladder infection itself. As this isn’t a surface-level infection, treating from within is the most efficient way to cure your pet fish.

White spot disease

White spot disease, or ich, is an illness caused by ciliated parasites (Ichthyophthirius multifiliis).

The disease manifests on aquarium fish as white spots and can cause fish to:

  • lay at the bottom of the tank;
  • rub against the substrate and other rough surfaces inside the aquarium;
  • display obvious signs of distress (lack of appetite, erratic swimming, etc.).

Causes

  • A weakened immune system;
  • Water temperature outside the fish’s comfort zone;
  • Poor diet;
  • Stress-induced response to being kept with incompatible tank mates;
  • Improper transfer (from store to home, or when being relocated in another tank);
  • Any stress factor that has a big enough impact on the fish’s immune system.

Treatment

  • If you’ve caught the ich in its early stage, raising the water temperature inside the fish tank can help kill the parasite. Aim for 78-80°F until the issue is resolved. Of course, don’t do this when keeping coldwater fish.
  • Medicate the affected fish for 10-14 days in a quarantine tank, using formalin, malachite green, copper sulfate, or methylene blue.
  • You can also try giving fish a potassium permanganate bath.

Learn how to give fish a potassium permanganate bath safely:

Visible wounds

Open wounds are an invitation for disease! That’s why you should immediately quarantine a fish that’s lying at the bottom of the tank and is visibly injured.

Quarantining wounded fish will also prevent them from being vulnerable, as some of their tank mates might opportunistically harass them.

Causes

  • Fin nippers;
  • Run in with bullies;
  • Fights for dominance, territory, or mating rights;
  • Accidentally bumping into decorations with sharp/rough edges;
  • Getting thrown about by a strong filter with a high flow rate.

Treatment

  • Address the factors that contributed to the injuries taking place in the first place.
  • Get a filter with a slower, or at least adjustable, flow rate.
  • Separate fin nippers, bullies, or territorial fish permanently from the wounded fish.
  • Replace sharp-edged décor items with smoother ones.
  • Quarantine the wounded fish lying at the bottom of the tank.
  • Treat the wounds, and prevent infections using an antibacterial solution, like MelaFix.

Conclusion

When fish lay at the bottom of the tank, it’s a good idea to monitor them closely, especially if this is a new behavior.

You now know what the concerning red flags that go along with this behavior are.

If your fish are just content to hang out near the bottom of the tank, there’s no reason to worry.

Consider adding a few additional décor items or live plants to your setup. Your fish will use them to rest without feeling exposed or vulnerable.

Resting without being on high alert will help your fish feel safe, and be confident and active the rest of the time!


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