How Many Fish Can You Keep in a 55 Gallon Tank?

If you have recently decided to upgrade your tank to a 55-gallon tank then you may be thinking to yourself that you can now have an abundance of fish.

However, this may not be the case. One thing to keep in mind is that tanks always actually hold less than the manufacturer prints on the box, meaning you can keep less than they claim you can.

As a general rule of thumb, however, you can hold anywhere from 3-4 fancy gold fish up to 40-50 ember tetras in a 55 gallon tank. The number of fish you can hold depends entirely on the type of fish you’re adding to the aquarium and what filtration system you have.

There are some general rules and guidelines that you can follow to help you understand just how many fish you can add to your aquarium without having the problem of overcrowding. To learn more, read on.

Fish pairings and groups

The first thing to consider when adding fish to your tank is which species you already have, or would like to add. The species is the biggest determining factor as a fish’s behavior can affect the number that can live comfortably together. For example, some more territorial fish will need to be fewer in number to allow them enough space.

Here is a list of some general numbers for certain species:

Type Of Fish# of Fish
Fancy Goldfish3-4
African Cichlids10-15
Dwarf Gourami8
-Male Dwarf Gourami2
Zebra Danios20-25
Ember Tetras40-50
Cardinal Tetras20-25
Neon Tetra30-35

It’s important to note that the numbers above (for goldfish) are for fancy goldfish only. Common goldfish need more space, so you can put 2 max. Ideally, I’d like to see them in a larger tank.

The numbers for danios and tetras are assuming a species only tank, so you may want to put less into your aquarium if you plan on keeping other species in your tank.


If you have worked out just how many fish and which species you can pair together in your tank the next thing to consider is your filtration system. Obviously, the more fish you have in your tank the more waste there will be and the better filtration system you will need.

If you have a good filtration system installed in your home aquarium then you will be able to keep as many fish as possible, obviously regarding that you have already determined the appropriate number and species. This will also stop your fish from getting sick due to the debris and waste produced by the others in the tank.

To ensure that your water filtration system is sufficient it must be able to pump and filter approximately four times the total volume of the tank per hour. So, if you have a 55-galloon tank then you are looking for a filter that can pump at least 220 gallons of water every hour.

You also want to consider maximizing the amount of filter media in your filtration system. When using a hang on back filter, this may mean getting something like the Aquaclear filter. Alternatively, you can get a canister filter.

General Rules of Thumb

If you are looking for a general rule of thumb to know how many fish you can keep in an aquarium, you’ve probably heard about the controversial “one inch per gallon” rule.

This rule means that you should put no more than one inch of adult fish for each gallon in the tank. (e.g. 50 gallons = 50 one inch fish or 25 two inch fish)

This rule is not the best in terms of accuracy and really starts to fall apart when you are talking about fish over 3″ long. The reason for this is that one 12″ fish is a lot larger than 12 1″ fish put together.

Because of this, you should only use this rule when looking at fish 3″ long or smaller – ideally 2″ or less.

If you are sure that you want larger species of fish, such as goldfish, then you will need to keep in mind that these require a lot more room than many other species and this will need to be accounted for.

The best tool to use when figuring out how many large fish you can keep – and to double check that your filtration system is enough – is Aqadvisor.

The amount of area your fish have to swim is another important consideration for how many fish you can keep. (And what type.)

When looking for a tank, it is better to opt for a shallow tank as opposed to a deep one as this will give you more surface area. Length X Width is more important than overall gallons. I would feel a lot better about putting fish in a 50 gallon breeder tank than a regular 55 gallon tank, because a lot of species of fish aren’t really going to effectively use the extra height in your 55 gallon.

Plus, that extra height makes it more difficult to clean.


There is no perfect number of fish to hold in a 55-gallon aquarium, and each tank will have its own specific optimum number depending on which species you want to house and the shape of your aquarium. 

It’s important to get an idea of what you’re going to put into your aquarium before you purchase them so you don’t end up with an overstocked tank.

You also need to make sure the fish work together – meaning that you’re not putting aggressive fish in with peaceful fish that are going to be bullied.

Take these things into consideration, and you’ll end up with a happy, healthy aquarium.