Finding the perfect match: Tropical fish compatibility

As Swell UK begins to retail more and more live fish stock of all shapes, sizes and colours, the question of what fish will cohabit with each other comes up more and more often.
And of course it does! It’s an important question in terms of the health and wellbeing of your fish, as well as the money from your pocket, where getting a pairing wrong often means a costly mistake.

Every time you consider adding a new fish to your tank, you need to go through the same thought processes to check that your plans are in keeping with the best interests of your existing tropical fish, as well as the newcomer:

Your tropical aquarium capacity

This is the first question to be asked. You might have spotted a colourful or interesting beauty in your local aquatics shop or online that would fit perfectly with the aesthetics of your tank. But is your aquarium up to the new challenge?

Every fish you add to your tank will have a profound effect on the long term quality of your water adding a surprisingly large amount of extra ammonia for your filtration system to deal with, as well as the obvious physical swimming space they take up.

Ask your stockist what kind of volume of water they are best kept in, and do a little math to see if your filter system’s LPH can handle it. Consider upgrading your biological media to something with a larger surface area if you have concerns about it’s ability to handle the extra waste.

Don’t forget to check ideal pH levels for your new fish, as well as their optimum temperature. You wouldn’t want to add your fish to your tank and realise that while your water chemistry was perfect for your old fish, your new one is going to struggle.

The short answer is: make sure your tank water is suitable for your new fish before you think about cohabitation with other fish. You might find that you fall at the first hurdle, and that new fish isn’t for you right now.

Fish behaviour

Once you have established whether your tank can handle the potential new addition, it’s time to look at how the new fish will get along with their new neighbours in their already established neighbourhood.

Firstly, you need to do plenty of research not only into your new fish, but your existing ones too. It could be that in your community tropical tank, your fish have been getting along just fine, but this new addition might spark a fight for dominance of a particular area of the tank, causing injury and death, or simply provide extra competition for an otherwise limited food source.

  • Territorial behaviour should be identified early on in your search for a new fish. While some species are happy to just keep swimming, others are fiercely about having their own patch, and are not happy to share. The most infamous being Fighting Fish, which as well all know, should never be kept together. Don’t forget to check your existing fish online for this trait too. It could be that you have had a very territorial fish in your tank all along, but in the absence of a challenger, they have seemed docile.
  • Food source competition needs to be looked at too. Algae eaters that have lived in your tank for some time might well have been perfectly happy, but should a newcomer mean competition, this might provoke an aggressive response from either fish, or cause a little starvation. Assess each fish’s diet and work out if you need to supplement their usual intake to keep competition down.
    Some popular profiles:


With such a huge and varied range of tropical fish available on the market, we can’t cover enough in one post, but here are some of the popular ones that make pairings easy:

Crown tail betta: Not considered aggressive, colourful displays. Only 1 Male in each tank (will fight otherwise), Females can sometimes be just as colourful and therefore can be paired (but risk obvious consequences).

Golden White Cloud/mountain minnow: Also not known for huge displays of aggression, this colourful creature likes to swim in schools so can be kept easily with an extra 2 or 3. Cohabits with other peaceful fish nicely.

Electric yellow cichlid: This one will most likely feel more confident (and therefore less aggressive) when kept in a school. Lone fish may however be more likely to be aggressive to other similarly sized fish if forced into too small of a tank. Consider this one for bigger tanks.

Georgina Posted by on

Georgina is a member of the Swell UK marketing team and has been keeping tropical fish for a number of years now. Her favourite fish being the stunning, male Siamese Fighting Fish. She is also looking to expand her existing collection to include keeping saltwater fish as well. Her other pets include Bengal cat, Walter, and Labrador and Rottweiler cross, Presley.

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