Keeping fish together

The number of fish you can keep in an aquarium depends not only on the water quality but also on the behavioural needs of the fish. For example, lots of fish in a tank will have to compete for food and they may become stressed. The number of fish you can keep together depends on the species of fish. 


Despite all goldfish being a single species, there are a great many varieties. Slim-bodied, short-finned fish with 'single tails' are the natural shape and are faster, more able swimmers and generally hardier. The other breeds aren't found in the wild, as they're 'fancy' varieties that have been bred by humans. They're slow moving and have shorter bodies and a 'twin-tail'.

Don't keep short and long-tailed varieties together, as you'll find the long-tailed fish will often miss out on food given their slower speed.

Tropical fish

Some tropical fish have also been bred by humans to produce new varieties, particularly mollies and bettas. It's best to choose species that live at varying depths of the aquarium to maximise the available space.

Remember, this page only gives a basic overview, and it's important that you research the species to find out their exact requirements, including:

  • Their natural environment
  • The water hardness they prefer
  • Their specific needs
  • Compatibility with other fish

Visit fish care and fish behaviours for further information.

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