Why is My Guppy Fish Laying on the Substrate?

Many novice fish owners struggle to understand their fish behavior, which is a pretty strenuous task if you ask me. There are countless species of aquarium fishes, each with its own behaviors and temperaments.

When it comes to guppies, there are two alarming behaviors that should concern you. Swimming near the water surface erratically and laying on the substrate. Today’s article will analyze the latter, explaining this rather abnormal behavior and seeing what triggers it.

If you’re a future guppy owner, you’re doing the right thing by looking for information about the species before purchasing your first pair. The more you learn ahead and the earlier, the easier it will be to identify and solve all issues that may arise along the way.

With that said, there are several reasons why your guppies swim or lay on the tank’s substrate:

The Female is in Labor

This is typical behavior for pregnant female guppies, getting ready to deliver. Mixing males and females in the same tank will inevitably lead to one or more females getting pregnant. You can tell by their full and rounded bellies that they increase in size as they’re getting ready to deliver.

The female will usually look for hidden and safe spots to deliver the fry when the time comes. Somewhere where they consider themselves safe. The females tend to remain motionless and float near the tank’s substrate when the act of birth occurs. It’s typical behavior that shouldn’t concern you.

Fast forward a few hours into the labor, and you will have dozens of guppy fry swimming around the tank. And since we’re on this topic, I recommend separating the pregnant female once the labor approaches. Removing it from the tank and placing it in another container will ensure the survival of the tiny fry post-birth.

Otherwise, they risk getting eaten by other adult guppies, including their own parents. To know when the delivery time comes, watch for the telling signs like, for instance, seeing the female swimming or laying on the substrate.

High Levels of Stress

There are a lot of things that could stress your guppies, leading to a change in behavior. One of the signs of a stressed guppy is the atypical behavior of seeking a hiding spot. This includes lurking around the substrate, searching for hiding areas behind plants, rocks, or other aquarium materials.

If you notice your guppy exhibiting a stressed behavior, try identifying and eliminating the things causing it. These may include:

  • The mating season – The female may experience increased stress due to the males’ mating behavior. If you have 2 or more male guppies in your tank, they will compete for the right to reproduce. This can make them extra pushy, stressing the females who will look for a way out.
  • Aggressive fish stalking them – If you have other fish in the tank, they may not get along with your guppies. Not all species can coexist in harmony, which means that your guppies can be at the wrong end of fish bullying. See if other fishes stalk or attack your guppies, which may cause them to go into hiding.
  • Overcrowding – Overcrowding can lead to an agitated fish population, more fish waste, and lower oxygen levels. All these will stress your guppies, causing them to appear lethargic and swim near the substrate. To avoid this problem, don’t overcrowd the tank. A 10-gallon tank should hold 5 to 10 medium-size guppies. These numbers will change when you add other fish species, varying in body size and volume.
  • Water temperature is too high – The hotter the water, the lower the oxygen levels. Low oxygen levels will affect your guppies’ immune system, causing them to swim erratically and experience fish sickness. It can also make them hyperactive as their metabolism accelerates due to the increase in water temperature.
  • Water temperature is too low – The colder the water, the less energy the guppies, will consume. They will appear lethargic, exhibit erratic swimming patterns, and fall sick more often. I recommend using a water heater which will allow you to monitor the water’s temperature and avoid dangerous fluctuations.
  • Accumulation of fish waste – Overfeeding your fish can cause unconsumed food to accumulate on the tank’s bed. The food residues will rot away, causing an increase in ammonia levels and affecting the water oxygen. This will affect your guppies’ behavior, causing them to float aimlessly in the tank or lurk around the substrate.

There may be more problems that will cause your guppies high levels of stress and affect their behavior. You can pinpoint the problem via a thorough elimination process or ask for professional guidance if you can’t solve the issue on your own.

Poor Water Quality

Many factors will affect the water quality, including overcrowding, fish waste, food residues, killing beneficial bacteria, etc. All these problems will eventually lead to a decrease in oxygen levels and a dangerous build-up of ammonia. Leaving these problems unresolved can cause your fish to fall sick and even start dying with time.

Poor tank conditions and water quality are the most common problems that beginners face, including overfeeding and overcrowding. I recommend cycling your tank before introducing the fish, changing around 50% of the water weekly, and removing fish waste regularly to prevent these problems.

A filter system is also a must, allowing you to clean the water and remove any harmful toxins without affecting beneficial bacteria cultures. An air pump is another key addition since it will keep the water oxygenated and fresh.

Bully Tankmates

Not all aquarium fishes get along. Some species will coexist with little-to-no issues, while others cannot stand each other. Forcing the latter species to cohabitate will lead to a variety of problems, including territorial fights, bullying, injuries, and even murder.

If your guppies will be at the receiving end of the clobbering, they will seek a way out fast. This includes constantly hiding behind plants and hovering around the substrate to minimize their profile.

The interesting aspect worth mentioning here is that even compatible fish can sometimes attack each other. If you have several species of fish living together, I always advise looking for signs of aggression. Guppies are small fish, and any larger species can bully them with ease.

Guppy Sickness

Numerous health problems could affect your guppies and alter their behavior. These include bacterial infections, parasites, dropsy, etc. The most noticeable symptoms include lack of appetite, erratic swimming, and lethargy, body lesions, changes in coloring, etc.

Your guppy may even display difficulty breathing and swimming and lay on the tank bed in search of comfort and relief. This sign, along with others, may suggest a disease, at which point you need to act fast.

If it’s a bacterial infection or tuberculosis, for instance, other fish will get it. To prevent that, you need to quarantine the sick fish until you figure out what’s going on. Moving the sick specimens to a different tank will prevent the spread and protect the healthy guppy population.

Ammonia Build-Up

Ammonia levels can spike for a variety of reasons. These include dead and rotting fish, the accumulation of fish waste, rotten fish food piling on the tank’s substrate, low oxygen levels killing the beneficial bacteria, etc. Ammonia is toxic to your guppies, causing a broad range of physiological symptoms. These include:

  • Partial or complete lack of appetite
  • Lethargic behavior without any apparent reason
  • Clamped fins
  • Erratic swimming pattern, either floating near the surface or lurking on the tank bed, etc.

Ammonia poisoning is deadly, and, what’s more alarming, the toxin can build up fast. It’s crucial to monitor the ammonia levels, especially in a larger tank with many different fish species. You can also prevent ammonia build-up by changing the water regularly and cleaning the tank whenever necessary.

Overfeeding is another contributing factor. I recommend feeding your fish only what they can eat at once; ideally, there should be no leftovers.

Swim Bladder Infections

The swim bladder is responsible for the fish’s buoyancy. Any problem with that organ will cause the fish to lose its floating capabilities and only swim near the tank substrate.

There are many causes that can trigger this problem, including overeating, constipation, infections, or parasites. If you can’t figure out the problem, I recommend speaking to a fish specialist and provide all the details you can. The expert will recommend adequate treatment depending on the problem’s nature.

If it’s a parasitic infection, you need antibiotics to solve the problem.


Fish lovers will usually look to get as many fish as they can from as many species possible. As a result, they will overcrowd the tank, making all fish uncomfortable and stressed. The fish will then grow more aggressive towards one another, leading to fights, attacks, and killing.

Your guppies can be overwhelmed in the process and seek to hide around the substrate, where there’s less activity. To prevent overcrowding, you need to find the ideal ratio between the number of fish, their size, and the water volume available.

Nighttime Sleeps

Guppies are diurnal creatures, which means that they are most active during the daytime. At night, they tend to sleep and rest near the tank’s bed when lights go off. It’s normal behavior that shouldn’t worry you. The only time floating near the substrate should concern you is when the behavior occurs during the daytime.


Guppies don’t generally lurk near the substrate like other fish species. They prefer the tank’s open waters with the occasional journeys to the surface to look for food. If you see them remaining near the substrate for long periods of time, you need to investigate the issue.

This article has touched upon the core problems that may affect your guppies’ behavior. If you still can’t get to the bottom of the issue, speak to a veterinarian or a guppy specialist to help you out.

avatar Noah
I’m Noah, chief editor at VIVO Pets and the proud owner of a playful, energetic husky (Max). I’ve been a volunteer at Rex Animal Rescue for over 2 years. I love learning and writing about different animals that can be kept as pets. read more...

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