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Fish Laying On Bottom Of Tank?: 16 Reasons Why & What To Do

Are your fish laying on the bottom of their tank? Often it’s no cause for concern, but if you’re worried check out our guide to 16 of the most common reasons.

By Julie Millis
Last updated on

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fish laying on bottom of tank

If you suddenly find your fish laying on the bottom of their tank it can be alarming. But there are many reasons why you may find them there.

We’ve seen this behavior many times in our aquariums, and more often than not it’s no cause for concern. Even when there are underlying issues they can usually be corrected as long as you know what to look for.

That’s why we’ve compiled a list of 16 of the most common reasons for fish laying on bottom of tanks. We’ll also show you how to properly diagnose any issues and what to do about them.

So let’s dive straight in!

When Is Fish Laying On The Bottom Of Your Tank Normal?

There are several reasons why your fish may lay on the bottom of your tank which shouldn’t cause you any alarm.

1. Adapting To A New Environment

It’s normal for your fish to lay on the bottom of your tank when first introduced to a new aquarium. 

Stress and anxiety caused by the move, or differences in water chemistry from their previous home, will lead most species to look for a place to hide. If your tank is bare, without rocks or plants for shelter, it’s likely your new fish will head for the bottom.

Zebrafish, for example, have been shown to stay at the bottom of a new tank, moving gradually higher as they become more used to their surroundings and their anxiety subsides [1].

So give your fish time to get used to their new aquarium. Depending on the species this can take around one to two weeks, especially if you’re adding them to an already established community tank.

2. Bottom Dwellers And Bottom Feeders

One of the more obvious reasons your fish may lay on the bottom of your tank is if it’s a bottom dweller. These fish spend the majority of their time swimming just above the substrate or often laying upon it.

Some bottom dwellers like suckermouth catfish will even burrow into the substrate to create nests when breeding [2]. Other common bottom dwellers include kuhli loaches, corydoras catfish, otocinclus, and plecostomus.

Many bottom dwellers are also bottom feeders and will spend much of their time laying on the bottom of your tank scavenging for food. These fish have ventral mouths at the bottom of their head. Some suckermouth catfish have even evolved to scrape algae from the substrate [3].

3. Sleeping And Relaxation

Like most animals, fish need to take time to relax and re-energize. The amount of rest your fish takes will depend on several factors like its species, age, and how active it is when swimming around.

Some fish will float in place, and others will lie on the bottom of your aquarium. You can usually tell your fish is resting if its breathing is regular and its pelvic fin is gently moving to keep it steady.

While sleep in fish continues to be researched, they do enter a ‘sleep-like’ state where their metabolism and activity slow [4, 5]. You can tell your fish is ‘sleeping’ if it heads to the same place each night, usually at the top or bottom of the tank, as has been shown in Zebrafish [6].

Many fish are diurnal meaning they are active during the day and ‘sleep’ at night [7]. So if your fish lays on the bottom of your tank at night it’s usually nothing to worry about.

Bear in mind light has a significant impact on the ‘sleep’ cycle of your fish [8]. So keep your aquarium lights on for 8 to 10 hours a day, and turn them off at night to allow your fish to rest.

4. Your Fish Is Getting Older

As your fish ages, you may see changes in its swimming behavior and how often it stops and rests. Older fish tend to consume less oxygen as their metabolism slows [9], and will often take more rest at the bottom of your tank.

Studies on Zebrafish have also shown that older fish swim along the sides and bottom of their tank rather than through the center [10]. Being close to or laying on the bottom can make them feel more secure than in the middle of the tank.

It can sometimes be hard to tell whether your fish is laying on the bottom of the tank due to getting older. But keep an eye on their swimming habits to see if they follow these patterns or start to hide more. You may also find older fish feed slower than younger ones.

5. Pregnancy And Substrate Breeding

Some livebearers like guppies may lay on the bottom of their tank when pregnant and in labor. Their larger size and high energy requirements during this time can cause them to seek a quiet corner for rest and security, particularly when giving birth.

Many species of cichlid are substrate breeders. This is where often the male will guard their eggs in a nest built into the substrate [11]. 

So if you see your fish laying on the bottom of your tank after breeding it may be exhibiting this parental care. And note that while it will move away, for example to feed, it will stay very close to the nest until the eggs hatch. Sometimes this can be for several weeks.

When To Be Concerned And What To Do

There are, however, several reasons why your fish laying on the bottom of their tank may be a cause for concern.

Betta laying on bottom of tank

Behavioral Issues That May Mean Your Fish Lays On The Bottom

Problems with tank mates, stress, or a poor diet can all lead to behavioral issues and cause your fish to lay on the bottom of their tank.

6. Poor Tank Mates And Aggressive Or Territorial Behavior

When it comes to tank mates and establishing territory there can be several reasons why your fish may lay at the bottom of the tank.

Many species will swim to the bottom of the tank and seek places to hide if they feel threatened by more aggressive fish [12]. On the other hand, you may sometimes find aggressive fish like African cichlids will lay at the bottom to establish their territory.

Possible Issues
  • Poor Tank Mates: If you own a community tank and see different species fighting for territory at the bottom, or fish hiding from others, they may be incompatible tank mates.
  • Wrong Male To Female Ratio: Some fish, like guppies, are prolific breeders. Males will constantly chase females to breed [13], which can lead them to hide at the bottom.
What To Do
  • Compatible Tank Mates: Research your fish and choose tank mates carefully. Bottom dwellers like cory catfish are a good choice to keep with bettas for example.
  • Create Boundaries: Use broad-leaf aquarium plants like Anubais to aquascape your tank and allow middle-schooling fish to establish territory away from bottom dwellers.

7. Boredom And Stress

Your fish may lay on the bottom of your tank due to boredom. Bettas, for example, need stimulation such as playing with toys. Without this, it’s common for them to lay at the bottom of their tank, and they can even become depressed [14].

Stressed fish will often try to hide at the bottom of their tank to feel more secure. This is especially true if your tank lacks plants or places to hide.

Possible Issues
  • Lack Of Stimulation: If your tank is bare you may notice your fish laying at the bottom as it becomes lethargic due to boredom.
  • External Stresses: Noise from outside your tank, or inquisitive pets pressing against the glass are some examples of external factors that can stress your fish.
What To Do
  • Create Interest In Your Tank: Use decor and planting to create areas for your fish to explore, hide, and rest. This will help prevent boredom and ensure they stay active.
  • Protect Your Tank: Make sure you keep loud devices such as televisions away from your tank and prevent people or pets from knocking against the glass. Use a tank lid to prevent cats or other pets from disturbing your fish, and stop them from jumping out.

8. Poor Diet And Eating habits

What your fish eats and how much can greatly affect its overall health. Depending on the species, your fish may need a higher fat-based diet for example. Fish that are fed a poor diet can often become weak and may lay at the bottom of their tank.

Possible Issues
  • Low-Quality Diet: A low-quality diet can leave your fish undernourished, and the lack of energy may mean they rest at the bottom of your tank more.
  • Overfeeding: Too much food, particularly for young fish, can cause bloating. Your fish may sink in the water and again lay at the bottom of the tank [15].
What To Do
  • The Right Diet: Research the dietary needs of your fish. Bettas, for example, are carnivores and need a varied, protein-based diet instead of too much plant material [16].
  • Stick To A Feeding Regime: It’s usually better to underfeed rather than overfeed your fish. Feed them twice a day and only what they can eat in 2 to 3 minutes.

Environmental Issues That May Mean Your Fish Lays On The Bottom

Often your fish may lay on the bottom of the tank due to issues with their environment. Take a look at the most common problems and what to do about them.

Goldfish laying at bottom of small tank

9. Your Tank Is Too Small

Overcrowding or keeping your fish in an aquarium that’s too small can have several knock-on effects. These can stress your fish, so it may seek refuge by laying at the bottom of your tank.

As well as a lack of physical space to swim and explore, overcrowding can lead to increased territorial behavior, whereas a larger tank can help reduce aggression [17]. This is why the general rule is to allow 1 gallon of space for each inch of fish.

A small aquarium will also lead to ammonia and other toxins building up in your water quicker, particularly if you have too many fish.

10. Your Water Temperature Is Too Hot Or Too Cold

Maintaining the correct temperature in your tank is critical to the life of your fish. For most tropical species it should fall between 74 to 80°F. But it must also stay consistent rather than fluctuating up and down the range.

If you see one or several of your fish laying on the bottom of your tank breathing rapidly this could be a sign of temperature shock.

When your tank becomes too hot, dissolved oxygen in the water is reduced as it’s lost to the air. As they struggle to breathe, your fish will move to the bottom of the tank where the water is cooler as the amount of dissolved oxygen is greater [18].

Cold water shock, on the other hand, can be even more severe. This rapid reduction in temperature can cause your fish to reduce its feeding and in turn, its movement to conserve energy [19]. So again you may see it moving slowly or laying on the bottom of your tank.

If your water is too hot you can use an aquarium chiller to slowly reduce the temperature. Or you can use a heater of the correct wattage for your tank’s size to warm it if too cold. But lower or raise the temperature gradually as rapid changes will shock your fish.

11. The Current Is Too Strong

Some fish like rasboras, zebra danios, and hillstream loaches thrive in stronger currents. But some, like bettas, prefer water with a much slower current.

So if you own a betta look for a betta filter that’s adjustable and will allow you to set a low flow rate. Otherwise, the strong current will stress your betta fish and you may see it laying on the bottom of the tank to avoid the flow [20].

You can also reduce the flow of your filter by covering the outflow with filter sponge, or by using plants or decor in front of it to break up the current.

12. Incorrect Water Parameters

Along with temperature, the correct water parameters in your aquarium are key for the health of your fish. As well as toxin levels, you need to maintain your carbonate hardness (KH), general hardness (GH), and particularly pH – which should usually be around 6.5 to 7.5.

A sudden drop in pH, sometimes caused by an associated drop in alkalinity [21], can be highly stressful for your fish. A drop to a very low pH, for example around pH 4.0, can reduce your fish’s ability to absorb oxygen, making them weak and can even lead to death [22, 23].

If your fish is laying on the bottom of your tank it could be a sign of a pH crash. So to avoid this, test your water parameters weekly with a test kit. You can even use a pH indicator strip that sits in your tank so you can give it a quick daily check as you feed your fish.

Diseases That May Mean your Fish Lays On The Bottom

There are also several fish diseases and related issues that can cause your fish to lay at the bottom of its tank.

Black neon tetra with white spot disease

13. Ammonia And Nitrite Poisoning

Aside from pH, toxin levels in the form of ammonia, nitrite, and nitrate are key to keep under control in your aquarium. Ammonia builds up in your tank from feces, and uneaten food and is also excreted directly from your fish’s gills [24].

It’s highly toxic to your fish and can be fatal at around 2.0 mg/l [25]. But as long as you have efficient biological filtration, ammonia will be broken down to nitrite, and then nitrate by your tank’s beneficial bacteria.

Nitrite can also be highly poisonous to your fish if it builds up as it prevents them from efficiently using oxygen in their blood [26]. You should manage your nitrate levels closely too as although it’s much less toxic, very high levels above 20 to 50 ppm can be harmful.

Symptoms To Look For
  • Physical Signs: Ammonia or nitrite poisoning can mean your fish’s gills look swollen or red in color. Breathing may also become slow and labored.
  • Behavioral Signs: As well as swimming slowly, your fish may move erratically or lay at the bottom of the tank gasping for breath.
How To Prevent Or Treat
  • New Tank Cycling: When setting up a new aquarium make sure you cycle your tank before adding your fish. This can take around 4 to 6 weeks
  • Monitoring: Monitor your ammonia, nitrite, and nitrate weekly. Both ammonia and nitrite should be close to 0 ppm, and nitrate should be below 20 ppm.
  • Water Changes: To keep toxins in check you should carry out water changes of around 20% at least fortnightly. But if your ammonia, nitrite, or nitrate levels are high perform a large water change (around 40%).
  • Chemical Treatment: You can also use an ammonia detoxifier in your water if the levels are too high. This is an efficient way to remove ammonia if your fish are showing signs of ammonia poisoning.

14. Ich (Or White Spot)

A common and highly contagious disease, ich (or white spot) is caused by the protozoa Ichthyophthirius multifiliis. It’s often triggered by stress in your fish due to sudden temperature changes, poor water conditions, or overcrowding.

Symptoms To Look For
  • Physical Signs: Small, circular white spots evenly spaced across the gills and body. 
  • Behavioral Signs: Your fish may clamp its fins, gasp for air at the surface, or lay at the bottom of the tank to scratch itself on the substrate.
How To Prevent Or Treat
  • Temperature: Raising the temperature in your tank by 1 to 2°F can help speed up the parasite’s lifecycle. But note although this will make it fall off your fish quicker it will still be present in your tank.
  • Chemical Treatment: To fully treat Ich, use a white spot medicine such as API White Spot Cure or Ich-X. These contain malachite green which has been shown to treat the parasite [27,28].

15. Swim Bladder Issues

Swim bladder disorders are a symptom rather than a disease but can be caused by bad diet, poor water conditions, and bacterial or fungal infection [29]. They can affect all fish but are common in mollies, bettas, and goldfish.

The swim bladder is an organ with a pneumatic duct allowing your fish to control buoyancy. Any issue with the swim bladder can result in erratic swimming as your fish struggles to control its movement.

Symptoms To Look For
  • Physical Signs: Your fish may have a swollen stomach or abdomen.
  • Behavioral Signs: You may notice your fish swimming erratically, have difficulty swimming to the surface, or become lethargic and lay on the bottom of the tank.
How To Prevent Or Treat
  • Water Parameters: Firstly, check your water quality and perform around a 40% water change if you notice your toxin levels are too high.
  • Check The Diet: Reduce the amount you feed your fish to around once a day for 3 to 4 days. You can also try providing high-fiber food like Daphnia.
  • Seek Advice: We’d always recommend speaking to a qualified veterinarian if you don’t see improvement after 3 or 4 days. Treating swim bladder issues can be very difficult if the cause is not properly diagnosed.

16. Fin Or Tail Rot

This disease is often caused by bacterial infection, particularly from several species of Aeromonas spp. [30]. There can be many underlying causes including poor water conditions, overcrowding, or your tank’s temperature being too low.

Housing incompatible fish, such as bettas with aggressive fin nippers, can also be a common factor. Once fin nipping has occurred bacteria can infect the wound and fin or tail rot may set in.

Symptoms To Look For
  • Physical Signs: Decayed fins with white or faded edges.
  • Behavioral Signs: Your fish may have difficulty swimming and spend more time laying on the bottom of your tank.
How To Prevent Or Treat
  • Chemical Treatment: Fin rot is often completely curable. You can treat it with antibacterials containing tetracycline (like API Fin And Body Cure) or kanamycin (such as Seachem Kanaplex). These are both effective against Aeromonas spp. [31].
  • Water Quality: Along with treatment, check your water parameters and perform around a 40% water change if you find the levels are too high. Also check your tank’s temperature is between 74 to 80°F.

What To Do Next?

There’s a multitude of reasons why your fish may be laying at the bottom of your tank.

Often this behavior is normal and will be due to your fish taking rest, sifting the substrate for uneaten food, or if they’re new simply adapting to their environment.

If you do notice any of the concerning behaviors we’ve covered above, including signs of disease, make sure you monitor your fish and take action where needed. 

And always remember to keep your tank well-maintained and monitor your water parameters regularly!

Frequently Asked Questions

Take a look at the answers to the most frequently asked questions as to why your fish may be laying on the bottom of the tank.

How Can I Tell If My Fish Is Resting?

If your fish lays at the bottom of the tank, particularly at night, it’s likely to be sleeping or resting. As long as it’s active at other times there’s generally no cause for concern.

What If My Fish Is Breathing Heavily At The Bottom?

A fish that’s breathing heavily at the bottom of its tank is seldom a good sign as it could be due to ammonia poisoning or disease. So check your fish carefully using the list above to guide you.

How Do I Know If My Fish Is Old?

As your fish gets older it may lose vibrance in its color, start to consume less food, and generally slow down and rest more at the bottom of your tank.

What Causes Betta Fish To Lay At The Bottom Of Their Tank?

Your betta may lay on the bottom of your tank due to stress or disease. But one of the most common reasons is the current is too strong. Lower your filter’s flow rate to solve this.

Photo of author
Julie Millis
Julie has been involved in aquatics for over 15 years. She is passionate about freshwater and saltwater tanks. Julie loves helping with all your fish-keeping questions!

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