A suitable environment for fish

Choosing an aquarium

It's important to make sure you set up the tank for the type of fish you want to keep. See these specific care sheets from OATA for information on particular fish types.


Bigger is better - always aim to provide more than the minimum required. Also bear in mind the eventual size of fish you want to get. Some fish grow very large and are unsuitable as pets. These include catfish such as the red tail, shovelnose and pangasius, plus the giant gourami and pacu. Always research the adult size of any fish you're intending to buy.


Position your aquarium away from heat sources such as direct sunlight.


Filtration is vital for removing waste from the tank. It takes time for beneficial bacteria to grow on the filter sponge which are essential in breaking down fish waste. Read more about biological filtration and water quality in our freshwater fish care sheet (PDF 556KB).


Goldfish will need to be kept within 10-21°C. Most other fish need a tank heater with a thermostat set to the correct temperature for the species. Find out about the temperature needs of different fish types by visiting the OATA website.


Artificial lighting is recommended during the day so the fish have a steady light cycle, as they would experience in the wild.


Working out tank volume:

In order to work out the volume of a tank before buying it, you can use this simple technique:

width (cm) x depth (cm) x height (cm) / 1000

For example, a tank measuring 60cm wide by 30cm tall by 30 cm deep has a volume of 54 litres.


Unsuitable aquaria

Goldfish bowls and fashion tanks

'Decorative' tanks, which include goldfish bowls, jars or children's tanks are designed as ornaments without any consideration for animal welfare.

  • The small size is inadequate (fancy goldfish require at least 60 litres of water each) and small volumes don't allow for a stable environment.
  • There isn't enough space for an efficient filter, so waste products can't be removed.
  • The low surface area means that not enough oxygen will be absorbed into the water.
  • Temperature levels can alter rapidly which can cause stress and even death.


We discourage the release of fish into outdoor ponds due to the damage they can cause to wildlife through predation and disease spread.

Sourcing fish

Picking healthy fish

Before selecting fish in a shop, consider the following:

  • Tanks should be clean and well maintained, without any dead fish.
  • Tanks should not have cloudy water.
  • Fish should be swimming effortlessly.
  • Watch out for split fins, white spot disease, open sores or underweight fish (concave bellies).

For more details on fish health, see our fish health and welfare page.

When to get your fish

We recommend using 'fishless cycling' when setting up a new tank. Only add fish once your aquarium has been set up and running for at least two weeks. You can read more about this in fish care sheet (PDF 556KB).

Did you find this useful?

Stay in touch

Sign up to receive our emails today. Get more pet care advice, hints and tips on helping wildlife, our latest news, rehoming success stories and more directly to your inbox.

Sign up to emails today