Why Do Fish Lay At The Bottom Of The Tank?

Understanding fish behavior can help you assess the health condition of your fish, water quality of tank and lot more. In this post we will talk about one of the common behavior of fish which is to lay at the bottom of the tank.

There are various reasons why a fish might lay at the bottom. First we will discuss why you shouldn’t worry about such fish behavior. After that we will point out reasons that will need your immediate action.

Why Do Fish Lay At The Bottom Of The Tank

Cause for no concern

Normal behavior

Laying at the bottom of tank is a normal behavior for some fish. Bottom feeder fish such as catfish primarily spent their time scouring the bottom of the tank.

As fish gets older, they have less strength and stamina. They are more likely to rest at the bottom then engage in any activity.


Many aquarium fish species sleep at the bottom of fish tank. Some may bury themselves in the sand or hide inside aquarium decor. Next time you see your fish laying at the bottom, don’t panic. It may just be taking a nap. You should, however, observe if the sleeping habit of your fish matches behavior of it’s species. For example, it is normal for nocturnal species to hide in the cave or lay at the bottom during daylight hours. However, if it lays at the bottom even after it darks then you should investigate further. It maybe a sign of disease.

Cause for concern

Aggressive tank mates

If your fish is getting bullied by other fish then it may swim to the bottom to hide. Watch out if your fish is getting constantly hounded by a particular fish to exerts it’s dominance. Such aggressive behavior can easily stress out your fish.To stop bullying make sure that there is enough space for fish in your tank. Fish can be territorial. If the bully fish is only one of it’s species in the tank then introduce another fish of it’s own kind. This will distract bully fish. Similar if the victim fish is also only one of it’s kind then add one or two of it’s species.  Bully fish are less likely to bully school of fish.

Ammonia Poisoning

Your fish may be laying at the bottom of the tank due to ammonia poisoning.

Ammonia poisoning damages gills and other internal organs of fish. Due to weak body function, fish loses appetite, becomes lethargic and lie down at the bottom.

Ammonia poisoning is a serious threat. It is touted as one of the primary cause of aquarium fish death.To prevent it, you need to do routine water change. Since rise in ammonia can not be seen, you need to regularly monitor ammonia level in water.

Nitrate Poisoning and/or Nitrate Shock

Nitrate Poisoning or nitrate shock is another reason why a fish may lay at the bottom.

Fish suffers from nitrate poisoning when there is a gradual increase in nitrate in tank water. Probable cause of nitrate poisoning are irregular tank maintenance, overfeeding and overstocking of fish. Instead of gradual change, if there is drastic drop or rise in nitrate level, fish suffers nitrate shock.

Considered to be less toxic than ammonia poisoning but it can be just as deadly, if let untreated. Adding live plants, feeding less, not overstocking and regular filter maintenance are some of the preventive measures you can take to stop nitrate poisoning.

Swim bladder disease

If your fish is suffering from swim bladder disease, it will either lay at the bottom or float near the top. It is a common disease that occurs in fish due to overeating, constipation and/or poor water quality. To cure swim bladder infection, quarantine the fish first and withhold food for 48 hours. Don’t feed your fish regular fish food until it’s condition improves. Feed peas or any easy to digest high fiber food 3 times a day for few minutes only.

White spot disease

You will find your fish laying at the bottom and rubbing against the surface if it suffers from white spot disease or ick. This disease is so common that most fish have well developed immune response against it. Aquarium fish usually develops white spot disease when their immune system gets weakened due to stress.

Things you can do

Maintain water temperature

You should regularly monitor water temperature because warm water can not hold the same amount of oxygen as cold water. Aquarium water should always have adequate level of oxygen. If there is drop in oxygen in water, fish will be put under great stress.

Warm water are less dense than cold water so they float at the top where as cold water sink to the bottom. This is why fish will lay at the bottom because it is the most oxygenated area of fish tank.

There are few things you can do to lower the temperature such as placing ziplock bag containing ice cubes on water, turning off heater and lights and removing aquarium cover. You can also use fan to drop the temperature. However, this may only work for smaller tanks. For larger tanks, aquarium chiller is a better option.

However make sure that water does not get too cold. Temperature of aquarium water should always be within the fish ideal temperature range. When water gets cold, it slows the fish metabolism making it sluggish and drowsy.

Routine tank maintenance

Without regular maintenance, aquarium becomes uninhabitable for fish. Routine water change will clean up fish excrement, decayed uneaten food and other build up waste from tank. Experts disagree on frequency of doing water changes. Some prefer to do weekly where as some prefer every other week. Crucial point is you have to do it regularly.

Test aquarium water at least once a month to check for any anomalies in water condition. Imbalance of chemical in water can cause havoc in aquarium ecosystem. It makes fish prone to getting sick and die.

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