Pet Keen is reader-supported. When you buy via links on our site, we may earn an affiliate commission at no cost to you. Learn more.

Home > Fish > How to Choose the Right Fish for Your Aquarium: 5 Vet-Approved Considerations

How to Choose the Right Fish for Your Aquarium: 5 Vet-Approved Considerations

woman buying aquarium fish

Vet approved

Dr. Luqman Javed Photo

Reviewed & Fact-Checked By

Dr. Luqman Javed

Veterinarian, DVM

The information is current and up-to-date in accordance with the latest veterinarian research.

Learn more »

Aquariums are a beautiful addition to any living space, workspace, or even bedroom. You will find aquariums of many sizes available on the market, from large to nano aquariums. When it comes to choosing the fish and stocking the aquarium, it is important to choose the right fish that will fit into the environment.

Choosing new fish for your aquarium is both a difficult and exciting process. It is better to first decide which fish you plan to keep before setting up the aquarium, as it can save you from all the trouble of having to find the right fish for your aquarium.

With a lot of research and careful consideration about the types of fish you are putting in your aquarium, you can create an environment in which your fish can thrive.


The Right Fish Matter – Here’s Why

So, you have set up your aquarium, and created a lovely environment with your preferred choice of decoration but don’t know what to stock it with? This is a common challenge many fish keepers face, but it is an important consideration when setting up an aquarium.

With so many different species of fish with diverse water and environmental conditions, not every aquarium you set up will be suitable for all aquarium fish.

Each species of fish has a different requirement for their aquarium, whether it is the size of the aquarium, the addition of a heater, the type of aquarium (freshwater, brackish or saltwater), or even the layout.

aquarium with cichlids fish
Image By: Frantisek Czanner, Shutterstock

You wouldn’t be able to put a goldfish in a small aquarium such as a 5-gallon tank that is better suited for a betta fish, but you might be able to keep a betta fish in a tank that is big enough for goldfish without housing them together.

It would also not be good to put a saltwater fish in a freshwater aquarium, as this is guaranteed to fail. Nor should you put a tropical fish that needs a heater in an aquarium that can’t fit a heater.

There isn’t one aquarium set-up that fits all species of fish, which is why it is preferable to research and decide on the type of fish you plan to keep inside before setting up the aquarium. However, if you haven’t done this, you can still find a species of fish to house in the aquarium, but you might need to make some minor changes depending on the type of fish you choose.

Preparing To Add Fish To Your Aquarium

Once you have the aquarium set up and decide to choose a fish, you first need to cycle the aquarium. The nitrogen cycle can get quite confusing, but to explain it simply, the nitrogen cycle is established in an aquarium when beneficial bacteria can convert your fish’s ammonia waste into a less or non-toxic form that will not harm them.

The Nitrogen Cycle Explained

Scientifically, these invisible bacteria that form a colony in filters, gravel, and in small amounts in the water column convert ammonia to nitrite, and then finally to nitrate which gets removed by water changes. Fish can tolerate higher nitrates than ammonia, and ammonia and nitrite are much more toxic to fish. However, high levels of nitrate can harm fish, but it will take longer to kill them, and it is easy to remove.

This process is important before adding any live fish into your aquarium and is often overlooked because the ammonia from their waste will kill the fish, and it is the main reason for early fish deaths when you first add them to an aquarium, known as “new tank syndrome.”

man changing water in aquarium
Image Credit: hedgehog94, Shutterstock

This cycle can take weeks to months to establish itself before the aquarium is safe for fish. You will need to run the aquarium filters during this process and add an ammonia source, such as fish food or household ammonia. You will need to regularly test the water with a liquid testing kit to find out whether or not the nitrogen cycle is completed.

The cycle is considered complete when you can dose your aquarium with 2 ppm ammonia in the evening and observe both ammonia and nitrite at 0 ppm the next morning, with the presence of nitrates.

Which Fish Are Right for Your Aquarium? 5 Important Considerations

When the aquarium has been set up and undergone the nitrogen cycle, you can now choose fish for your aquarium. This is undoubtedly the most exciting part of setting up your aquarium, but you will need to consider these five factors before choosing just any fish.

1. The Size of the Aquarium

Each species of fish has a different minimum aquarium size that supports the fish’s size or schooling habits. Smaller tanks are better suited for fish that do not grow very large and can thrive in a smaller environment, such as the betta fish that can do well in a tank as small as 5 gallons.

Other common pet fish such as goldfish and cichlids require a larger aquarium, as they grow very large and produce a lot of waste. These big fish won’t thrive in a small aquarium and are better suited for larger aquariums.

Schooling fish such as tetras need to be kept in groups, and even though they are small, still require a medium to large-sized tank to support their schooling habits.

Image Credit: rodimov, Shutterstock

2. Type of Aquarium

Aquariums are available in different shapes and sizes, so you should consider the aquarium’s vertical and horizontal space when choosing your fish.

The decorations inside of the aquarium don’t matter much, unless you plan to get a fish that prefers a certain setup, like plecos that benefit from driftwood in their aquarium as it is part of their diet. Most fish will appreciate live plants in the aquarium, but it is not a necessity for most species.

The shape of the aquarium can also influence the type of fish you keep, as lionfish and South American tetras can be kept in tall aquariums with more vertical space, while most species of fish do better in aquariums with more horizontal space.

Bowls, vases, and bio-orbs are usually too small for fish, which is why invertebrates such as shrimp or small snails are a better option depending on the size.

A standard rectangular tank is ideal for most species of fish, and some of the most common schooling fish like tetras, or social fish like goldfish do best in a rectangular type of aquarium.

aquarium glass cleaning
Image Credit: hedgehog94, Shutterstock

3. The Filtration System

A filter is an essential part of the aquarium, and it is responsible for keeping the water clean and moving. However, each filtration system is different and better suited for certain species of fish.

Strong filters are ideal for fish that produce a higher bioload and are considered messy as they will help to remove more of the waste from the aquarium quicker. Filters may also influence the amount of aeration and movement in an aquarium, with some species of fish such as the danio, hillstream loach, or rasbora prefer a current in the aquarium produced by the filter, whereas long-finned fish like bettas do not.

A small betta fish that is living in a smaller aquarium won’t need such a big filter and aquarium as a goldfish would, and both these fish don’t need much of a current.

aquarium filter
Image Credit: Andrey_Nikitin, Shutterstock

4. The Water Conditions

Each aquarium will have different water conditions, with a specific pH, temperature, and salinity. Although most aquarium fish aren’t too fussy over the pH level in the aquarium, there are fish that do better in either alkaline, neutral, or acidic waters.

Fish such as the red-tailed shark do better in softer water that is more acidic, whereas goldfish prefer a neutral or slightly alkaline pH.

If your aquarium is salt water, you can only stock it with marine fish that need a higher salinity content in the water to live, while freshwater fish do not require any salt unless they can live in brackish conditions.

Researching the fish’s water conditions is important, as you can’t keep a freshwater fish like goldfish in a marine tank and vice versa.

Aquarium Test Kits
Image Credit: M-Production, Shutterstock

5. Heating Equipment

Depending on where the fish originated from, in either tropical, temperate, or cold waters, it will affect what temperature the fish need in the aquarium. Tropical fish such as bettas, tetras, guppies, and platies need a heater because they originate from waters that have a higher temperature.

Placing them in a tank without a heater that has cold or fluctuating room temperature water is not a good idea, as a heater is important for these fish. Temperate or cold-water fish like goldfish and white cloud mountain minnows do not need a heater, and they will be fine at room temperature unless the temperature becomes too hot or too cold.

Aquarium Tank heater
Image Credit: Huy Phan, Unsplash


Final Thoughts

Choosing the fish you want to add to your aquarium is a fun experience, but you will need to do plenty of research on the specific species of fish you have in mind before purchasing them. Make sure that you have the right aquarium, filtration, heating, and water conditions for your fish species, and make any adjustments to the aquarium if needed.

There is no “one type fits all aquarium” that meets the criteria for each fish in the hobby, which is why the aquarium should ideally be set up specifically to meet the care requirements for the fish species you have in mind.

Featured Image Credit: hedgehog94, Shutterstock

Our vets

Want to talk to a vet online?

Whether you have concerns about your dog, cat, or other pet, trained vets have the answers!

Our vets