Cold Water Vs Tropical Fish: Deciding Which to Get

Are you planning to introduce an aquarium to your home? There are thousands of different fish species to choose from but one of the most important decisions that you’ll need to think about is whether you’ll choose cold water or tropical fish.

It’s important to understand the likes and dislikes of both so that you don’t mistakenly set up an unsuitable aquarium, causing distress to your fish.

This blog explains the difference between cold water and tropical fish, and goes through some of the things that you should consider when choosing fish, especially if this is the first time that you’ll be owning them.

What are the Differences Between Cold Water and Tropical Fish?

Cold water fish are happier living at cooler temperatures, typically below 20°C (68°F). They don’t require their water to be heated, and instead their tanks are best left at room temperature.

Examples of cold water fish include goldfish (of which there are over 100 varieties), black moor and shubunkin.

On the flip side, tropical fish need their water to be at a higher temperature to be healthy and comfortable. The optimum temperature for a tropical fish task usually ranges between 25° to 27°C (76° to 80°F) although different types of fish have different requirements. Always check with the specialist at the shop when you’re looking to buy a particular type of fish.

Examples of tropical fish include guppies, neon tetra, platy and angelfish.

There is another type of fish, known as temperate fish. Preferring to live in water at a temperature of 18–23°C, their ideal environment is somewhere between that of a cold water and a tropical fish. They don’t usually need a heated tank and can live in an aquarium at room temperature as long as the room itself is centrally heated.

White Cloud Mountain Minnow and Dario are examples of temperate fish.

Whichever type of fish you decide to go for, it’s a good idea to have an aquarium thermometer set up. This way you can keep an eye on the temperature, and ensure it’s at the optimal level for your particular species of fish.

Can You Mix Tropical and Cold Water Fish?

Tropical and cold water fish shouldn’t be mixed, so you’ll have to decide whether you want cold water or tropical species in your tank. There are a number of reasons for this:

  1. Because they appreciate different water temperatures, it is very challenging to find middle ground that will suit both types of fish.
  2. There is also a risk that if one species falls ill, the other will not have sufficient immunity for that disease. This can mean that they ultimately kill each other off.
  3. Cold water fish have a metabolic rate designed to function at a much lower temperature. Keeping them in a tank with tropical species at warmer temperatures will result in much shorter lifespans for the cold water fish whose metabolic rates will have been kept at an unnaturally high rate.
  4. Cold water fish tend to produce more waste than tropical fish. Keeping them with tropical species can result in levels of ammonia in the tank that the tropical fish cannot tolerate. This can prove fatal if the filtration system isn’t up to scratch.
  5. Different types of fish have different diets. You shouldn’t feed goldfish tropical fish flakes for example, as they will have different levels of nutrients to what they need.

Which are Better for Beginners, Cold Water or Tropical Fish?

Many new fish owners shy away from the idea of having a tropical aquarium as they fear that it will be too much of a challenge. However, tropical aquariums are not as much hard work as you might think, and they can actually be easier to care for than cold water fish, making them a great choice for beginner fishkeepers.

There’s a misconception that because tropical fish require a heater, cold water fish are easier to keep. In reality, both kinds of fish will require you to keep an eye on the temperature, as well as PH levels, lighting and filtration systems. Then there are other additional considerations to take into account with cold water fish, which we’ll go into in more detail below. Not only do they tend to grow larger, requiring bigger tanks or even outdoor ponds, but they create more mess than tropical species too.

5 Things To Consider When Choosing Your Fish


Firstly, many species of cold water fish will grow a considerable amount. They need to be kept in larger tanks to accommodate this growth potential and avoid overcrowding.

Even very large tanks are not always enough for some cold water fish. To avoid stunting the growth of goldfish or koi for example, it’s kinder to let them live in an outdoor pond. This will give them plenty of space to move around and reach their full size.

Tank Space

As well as taking into account the size your chosen fish will grow to, you should also consider the water depths they like to swim at. Having a variety of fish that like to live at different depths in the aquarium will maximise the available space.


Both tropical and cold water fish need good filtration systems, but this is particularly important for goldfish due to the large amount of mess that they can create.

Fish waste contains high levels of ammonia which is very toxic to them, so cold water fish will need excellent filtration systems to keep their water clean.


Don’t introduce fish to an aquarium without first finding out whether they’ll get on with each other. Not all species of fish will be compatible; some fish will nip the fins of other fish, eat them, exhibit territorial aggression, or simply grow too large.

Fish that can live together in harmony without fighting or eating each other are known as community species. Some examples of tropical community species include rainbow fish, guppies, tetras, rasboras, danios, Bristlenose catfish, and Corydoras catfish.

Despite being the same species, it’s not advisable to keep short and long-tailed varieties of goldfish together. Long-tailed goldfish move more slowly and might often miss out on food.

If your chosen fish are not compatible, they can become very stressed. High stress levels can lead to ill health, weakening the immune systems of your fish and making them more susceptible to diseases.


Different fish will have different requirements when it comes to enrichment opportunities. For example, some species of tropical fish like catfish will need caves and hides to make them feel secure, while other fish will be happy with rocks and plants for their shelter and shade.

Wrapping Up

Fishkeeping can be a very rewarding hobby, but it can be time-consuming and expensive, so make sure you’re well-informed and prepared for what will be required of you before buying your first fish. If you have particular fish in mind for your aquarium, be sure to do some research into their different personalities, needs and behaviours first to make sure that they will be a good mix. Despite what you might assume, tropical fish are great for beginner fishkeepers, and may be better suited to you than cold water species. Always speak to a fish specialist or your veterinarian if you have any questions or concerns.

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