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Tropical vs. Cold Water Fish: The Main Differences

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When you want to add fish to your tank, you encounter a wide variety of beautiful species. Something to bear in mind might be the requirements and preferences of each species. Here is where knowing the difference between tropical and cold-water fish comes in handy. 

The main difference between tropical and cold water fish is the temperature requirements. These requirements also influence the equipment needed to keep these species happy in an aquarium. Apart from the temperature, space, appearance, and variety might also be remarkable differences.

There are many details to consider when becoming a fish keeper. It is crucial to understand the differences between the species and the habitats to provide the best care to your fish. Keep reading to have all the insights!

What are tropical fish?

Tropical fish are species found in tropical waters all around the world. These species tend to prefer heated aquariums. Some of the most common species of aquarium fish are tropical fish. Among these, we find tetra fish, betta fish, and many more.

Tropical fish cannot survive low temperatures. Since they come from tropical regions, regulated and controlled temperatures are the best condition for these species. Anything around 22 to 26 degrees celsius would be perfect for tropical fish.

To reach these conditions, you might need a submersible heater for your tank. Many beginner aquarists take this as a troublesome requirement and often steer clear of having tropical fish. 

The truth is that tropical fish might require less care than cold-water fish, so many beginners prefer to debut in the fish-keeping hobby with tropical fish. Another thing to consider is that many stores and pet shops will have a wide variety of tropical fish available.

A lot of species can be classified as tropical fish, making it difficult to talk in general terms about the requirements and care of tropical fish as a whole. Each species and subspecies will have particular needs you need to be attentive to.

Despite what you might think, not all fish species are compatible. In some cases, your fish will not get along, and you will not be able to keep them in the same tank. Knowing the compatibility of your species is also crucial.

Some big species might become predators and cause problems in your ecosystem. Be careful with this to protect your beloved fish.

The best way to care for your fish is to know the species you have and follow their necessities. Avoid any overgeneralization and get to know your fish. They will thank you for it!

What are cold water fish?

Cold water fish are species normally found in cold waters around the world. Despite what their name suggests, the temperature requirements of these species are not that low. These species can be kept at room temperature without using a heater in the aquarium. 

The main characteristic of cold water fish is that they don’t need a heater to survive in a tank. Room temperature should be more than enough to provide adequate conditions for these species. Most cold water fish prefer temperatures around 20 degrees Celsius and below. 

Some of the most known species of cold water fish are koi and goldfish. They can be kept in outdoor ponds without worrying about their survival if the temperature drops. The natural habitat of these species includes lakes, ponds, and rivers that freeze during the Winter. 

Something to bear in mind is that most species of cold water fish require a lot of space. These species need more space than other varieties of fish. 

Just as with tropical fish, overgeneralization could be harmful. There are many species comprehend under the category of cold water fish. In this sense, each species could have different requirements that you need to know to provide the best possible care.

One common requirement of most species is the constant need for filtration. Cold water tanks need to be filtered very often to maintain water quality. Regular filtration will provide the most optimal conditions for cold water species. 

In many cases, cold water species might prefer similar temperatures to tropical species. The cold water denomination only refers to high tolerance to low temperatures if they came to appear.

This misconception is why many fish keepers have their cold water fish in way too low temperatures. Once again, knowing your species will be of great help here. 

Main differences

To better understand how these species differ from each other, we will look at the following criteria in detail:

  • Temperature
  • Heater requirement
  • Appearance
  • Variety
  • Tank size
  • Filtration requirements


The main difference between these two species is temperature. Their names are an easy giveaway of this. Tropical fish prefer temperatures around 22 to 26 degrees Celsius because that emulates their natural habitat.

Tropical fish come from tropical waters all around the world, so these temperatures are perfect for them. In contrast, cold water fish usually come from colder areas. Although they don’t always prefer low temperatures, they can thrive in them too. 

It is essential to get to know the species you have in order to provide the preferred temperature for them. Something to note is that finding middle ground in the conditions for both tropical and cold water fish might be a nearly impossible task.

I would recommend against mixing both varieties in the same tank, as the fish could stress and get ill. 

Heater requirement

When it comes to tropical fish, having a heater is not even a question; it is a requirement. Tropical fish need a controlled environment without sudden temperature changes. Trusting room temperature might be unproductive and harmful to your fish.

The other alternative is to have a temperature-controlled room. However, this might end up being more complicated than just looking for a reliable heater for your tank.

Cold water fish, on their part, thrive perfectly in room temperature waters. Whether the temperature falls or rises a bit, most cold water species will be just fine. Yes, the name says cold water fish, but that is not actually the case.

Calling these species “room temperature fish” would have been a marketing bummer if you think about it!

Some aquarists like to have heaters in their cold water aquariums to ensure a steady and regular temperature either way. That would be a personal decision.

Whether tropical or cold water, aim for a reliable, high-quality heater and be sure that it is working effectively. After some time, heaters could fail or malfunction. If you don’t notice this on time, your fish could suffer. 


Tropical fish are more colorful than cold water fish in general. Remember that these will have to do with the species and the different varieties of each one. However, it is common for cold water fish to have milder colors.

Nowadays, there are many tropical fish species with dashing colors available in most pet shops. You just need to choose a colorful species to brighten up your ecosystem. 

With this I don’t mean that cold water fish are not beautiful. It is just that tropical species tend to have more colors and more exotic combinations. 


There are considerably more tropical fish species available for aquarists. Most pet shops have a great variety of tropical fish in-store, but not as many cold water species.

In this sense, it is more common to see exotic varieties of tropical fish around. Tropical fish are more accessible and can be found more easily. These species have also been adapted to nano tanks, making it easier for beginner fish keepers to have them. 

Tank Size

As said before, tropical fish have been adapted to nano tanks. They don’t require a lot of space to thrive and live happily in an aquarium. With a 10-gallon tank, your tropical fish should have enough room. 

That is not the case for cold water fish. These species require a lot of space to move and stay healthy. Take, for instance, goldfish. The healthy growth of a goldfish will depend on how much space it has to move. Not providing enough room could make goldfish sick and affect their growth. 

In many cases, cold water fish will be better kept in outdoor ponds with enough space to move around. These would be the most optimal conditions for cold water fish. Thanks to their tolerance to low temperatures, you needn’t worry about the temperature harming your fish.

Have you seen those koi ponds? They are so beautiful and effective for a reason! Be sure to provide enough room for your cold water fish to thrive. 

Filtration requirements

Cold water species might need more filtration than tropical species. However, this will largely depend on the species you have. Goldfish, for instance, are known to be quite messy. For tanks or ponds with goldfish, regular filtration might be necessary.

Tropical species don’t need as much filtration, but don’t get too comfortable with this! All fish species will need clean water to thrive. It is just that tropical fish might produce lower levels of ammonia, which is toxic to fish. 

At the end of the day, the rule stays the same: know your species. The differences here outlined are just general parameters and characteristics of tropical and cold water fish. However, each species within these categories could have all sorts of requirements.

Get to know your species to help them thrive and develop in your aquarium!