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Can A Fish Disappear From A Tank ? (12 Possible Reasons)

Can A Fish Disappear From A Tank? If you are an aquarist, This may be a big question for you. I know if it happens it will break your heart. However, do you know the extract reasons for fish disappear?

Can A Fish Disappear From A Tank

Sometimes you may experience that some of your fish are gone when you turn on the light during the daytime. How does it happen? Does a ghost eat your fish at night? Bit curious, know?

Read the full article and gain some exciting facts about why fish despair from the tank!

Why does a fish disappear from a tank?

There are several ways to disappear fish from your tank. Some of them are jumping out fish from the aquarium, being prey for large fish, and hiding between tank ornaments.

Do you know that most fish disappear because of your mistakes? So, it is your responsibility to protect your fish and keep them for a long time under your care. 

01. Sickness

Every creature has to face many illnesses and diseases during their lifetime. So, sickness is a common scenario that every fish have to face. 

But how do fish diseases relate to fish disappearing?

Generally, when fish suffer from any disease, they are not like to expose to the outer environment. So, they always try to hide in the caves, ornaments, aquatic plants, and other rock structures.

On the other hand, this tendency is high if you have a saltwater tank. Saltwater fish diseases progress very quickly and damage the fish.

So, these infected fish show behavioral changes, and they always try to loll near the tank bottom. 

If you did not notice them at this stage, surely you may think these fish are disappearing. Because once they are severely affected, they hide in substrates of your tank, such as coral caves. So, it is difficult to see them if they hide. 

On the other hand, if infected fish die, the other fish and invertebrates can eat them. As a result of this, your fish will disappear within a short time. 

Therefore, you should keep your eye on fish behavior and should identify the changes. If you notice when they in stressed, take quick action and follow suitable treatment. If not, they will permanently lose.  

However, if you are a lucky owner, you can see your fish after a few days. How does this happen?

Some fish hide in a secure place and gradually recover from the disease. In this type of situation, you can see them with normal behaviors after a few days. 


I know you do not want to be an irresponsible aquarist. So, to prevent these types of incidents, follow some good practices!

  • Do some research and make sure all fish species and invertebrates are compatible
  • Maintain the water quality of your tank at optimum levels
  • Add enough food for fish at sufficient intervals
  • Being careful and do not disturb the tank inhabitance

02. Jump out by accident

Some fish tend to jump from the tank. This is mostly happening in the aquarium, which has not a roof.

However, if your tank is enclosed by the roof and has some gaps, fish can disappear from them. No wonder! Yes, some fish can jump out from the small spaces. 

Anyhow, if you do not notice the moment when they jump out from the tank, most of their lives end up with a painful death. 

When fish fall down to the floor, they move their bodies and fins. Also, fish has a very soft body. Due to these reasons, they slip on the floor and escape under tables, sofas, and any other furniture. 

Due to lack of oxygen, they will die on the floor. On the other hand, they may damage while landing on the floor. These injuries and shocks can kill fish.


This is a serious case. So, once you notice fish disappear from the tank, immediately look around. If your tank mounded on a stand, look at its behind. 

Here, some fish die because of falling shock. But some fish can survive for some time. Especially, the fish with labyrinth can live for quite a long with after falling from the tank. 

If it lucky enough to live, you can find them before you die. If you find these fish on the floor, immediately put them into the tank. Then carefully observe its behavior and check whether it has recovered. 

Here, you can add some tension coating to the water. It will help fish regenerate the slime coat that damages when put on the floor.

However, falling fish are more susceptible to disease. Because of their organs, outer skin damage, and exposure to the outer area. 

Therefore you should pay attention to them until they fully recover. Be aware of how other fish react toward fallen fish because weakfish can be the prey of others. But if you are too late, you have to say goodbye to your lovely one. 

Can A Fish Disappear From A Tank

03. Predation by others

Predation by other fish is the most common reason that causes your fish to disappear within a few seconds. How is it happen?

Fish have different kinds of feeding behaviors, and according to it, they divide into the carnivore, omnivores, and herbivores.

For example, Arowana, Arapaima, Pacu, and Aligator are the most famous freshwater carnivore fish.

So, if you add small fish like guppies, platies, swordtail, and tetra species to their tank, do not wonder; they will definitely disappear shortly. 

Because carnivore fish think the small fish are their prey. So, they catch and happily eat your tiny pet. That’s why we always advise putting compatible tankmates together. If not, the little fish’s story will end with unfortunate death. 

Further, do not blame carnivore fish for it. Because according to the food web, they were born to eat small live creatures. Thus, it is your responsibility to protect every fish in your aquarium.

This story is the same as a saltwater aquarium. Live rock doesn’t offer enough spots to hide your small fish.

So, large fish can find them easily. Also, in the saltwater aquarium, plenty of species live. Crabs and shrimps become a significant part of it, rather than common fish. 

However, when fish are sick and attacked by other fish, they get weak. Ultimately there is a possibility of dying them.  

However, if they die in the saltwater aquarium, the crabs and shrimps can eat their corpses. Due to these activities, there is a high possibility of disappearing some fish from the aquarium. So, do not ignore the small facts. Keep your eye on it. 

04. Lots of tank mates

Every tank has its own capacity. So, it can tolerate a certain number of fish amount. However, most beginners do not know this. They add a huge amount of fish into the same tank to enhance its beauty. 

On the other hand, after adding lots of tankmates. They forget how it will affect water quality. Every fish and water creature releases their excretory matters into the water.

So, if you add lots of fish into one aquarium, these fish produce massive excretory mass. Due to that, the tank’s nitrate, nitrite, and ammonium level rapidly increase. 

Also, every fish has an optimum range of specific water quality parameters. But when water quality parameters change, they can not control it anymore. As a result, they tend to stress and die. 

However, this process is not finished here. If you do not remove dead fish immediately, they start to decompose and further influence o water quality. Ultimately, it will cause other fishes to die. 

The fish tank is a closed system. So, everything can affect other things. Its effect circulates throughout the whole system.

Hence, sometimes these conditions can kill all fish in your tank. Or else, due to unfavorable conditions, fish may tend to jump from the tank. 

05. Water quality

Fish lives mainly depend on the tank’s water pH, hardness, dissolved oxygen level, Salinity, and pureness.

Also, the freshwater fish’s requirements change from the saltwater fish. Thus, it would be best if you separately treat them. 

Moreover, the water quality requirements will vary according to the following factors. 

  • Fish species
  • Size
  • Age range
  • Number of tankmates

So, each one has special water quality requirements. Thus, the aquarist should maintain them at the optimum level. However, if water quality parameters worsen, fish may show the following reactions. 

So, if you do not take corrective actions immediately, your fish may disappear from the tank. 

06. New tank mates

Did you add a new tankmate yesterday and notice your one fish disappear? Yes, it can happen. There is a possibility that new fish will become prey to other fish. Or else your newly added fish can think; that other old tankmates are their prey. 

Both incidents can happen in the aquarium. So, it is vital to select compatible tankmates if not one fish become prey to another fish. 

However, sometimes you may think the new one is compatible with other fish. But how did the new one disappear? 

Sometimes, when you add new fish to your aquarium, other fish need time to identify and build a relationship with them. However, if other fish are in the wrong mood, they can attack the new one. 

Therefore, when adding new fish to your tank, always pay attention to the aquarium and see the other fish’s behaviors.

Removing them before disappearing from the tank is better if they continuously show aggressive behaviors towards the new one.

Can A Fish Disappear From A Tank

07. Big fish

Big fish means they have big mouths. So, when you add big fish and small fish into the same tank, you should pay full attention. Primarily you must check these species are compatible. 

However, after you add compatible species, some fish may disappear. How does it happen? 

Think, your aquarium has big omnivore fish. They do not show aggressive behavior until all conditions are favorable and food is not a limiting factor.

However, if you forget to feed them at the correct time and when they are suffering from food deficiency, they attract small fish that fit their mouth size. 

08. Strong currents

Some fish love these currents, and some fishes need calm waters. The strong current turbinates the water, and it can badly affect some fish species. Especially who love to live in a calm and peaceful environment. 

The turbid water encourages fish to swim near the water’s surface and jump from the tank. Also, it causes stress on the fish.

Because of stress, these fish are more susceptible to diseases and always try to hide in the caves. So, if your tank has this kind of condition, immediately reduce the current speed. 

09. Eternal threats

What are the external threats that disappear your fish?

There are many. Birds, Snake species, and Frogs are the major parties responsible for this. If your aquarium setup exposes you to the outer environment, especially if it hasn’t a sealed roof, you can lose your fish. 

So, don’t let your fish become a snack of them. Create a proper roof and protect them. 

Rather than this, some people also can be an eternal threat to the fish. Think, how many times have you knocked out to the glass of your tank? 

Some visitors do this for fun and enjoy the motions of the fish. However, some fish don’t like this type of disturbance.

It will end up by jumping them outside of the tank. So, always try to let them live in harmony and natural peace. 

10. Lots of open spaces

We always advise that if you add any semi-aggressive and peaceful fish together, add enough aquatic plants. Do you know the reason behind it?

Generally, we cannot predict the behavior of semi-aggressive fish species. They will live calmly until their environmental factors are favorable.

However, if these factors exceed the limits, they may tend to attract and eat their tankmates. 

However, in this type of situation, open spaces help them to catch their prey easily. So, you should add some aquatic plants, ornaments, and caves to your tank. They act as a protective cover and give hiding places to peaceful fish species.

11. If they are alone

Some fish highly seek a company.

They are very active at community tanks. But if you add them alone, they will lose their interest in being active and try to hide inside the ornaments and corners of the tank. Thus, do not put shooling fish along. Add them into a community tank. 

12. Bright sunlight

Fish have different biological requirements, especially at different stages of their life.

Some fish love to spend dark conditions during their breeding time. Also, some others like to live in dark conditions throughout their lifetime. 

However, if you keep this kind of fish under high light intensity, they get stressed. As a result, these fishes tend to hide in dark areas of your tank. So, check the pots, caves, and inside the ornaments to find out your fish. 

On the other hand, the bright sunlight heats the tank and tank water. Due to that, the dissolved oxygen levels of the tank reduce. It also acts as a stress factor. 

Can A Fish Disappear From A Tank

How do you find missing fish? 

Now you have a better understanding of how your fish disappear. You can find them in live status if you are a lucky aquarist.

However, sometime they will die while you are finding them. However, at the first moment when you notice your fish is missing, check the below facts.

  • If your tank does not have a sealed roof, check out the surrounding. If there have any evidence of water spills, check out the surroundings. Especially under the furniture, mats, and behind the tank stand
  • Give a small knock to your tank glass and check whether any fish move. Sometimes they come out from the hide spaces for a while
  • Check are there any skeleton or muscle parts on the bottom of the tank 
  • Check the behavioral changes of big fishes and their stomach sizes
  • See surroundings and check whether any foreign animals are there
  • Check if any damage happened to the roof of the tank

Using the above inspections, you can find out what happened to your fish. 


There are several ways to lose your fish. So, you must control these things and keep them securely under your care.

I hope this article gave good knowledge about it. So, if you notice any issues, correct them immediately. Then both you and your fish can live happily for a long time!

Credit to : Majestic AquariumsTV
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About Dr.Chamika

Hello, I'm Dr. Chamika. I am a Researcher in Water quality, Aquatic organisms, and Environmental chemistry. I am a passionate fish keeper, with10 years of experience. My mission is to help other aquarists experience the joy of fish keeping.