Advice on how to choose the right species of fish for your aquarium.
There are so many fish to choose from it can be daunting and confusing for beginners. Many people are put off fishkeeping because they choose the wrong fish for their tank and are unable to look after them. Choosing the right fish is very important but is not difficult providing you do a little research. What type of freshwater fish you ultimately get will depend mainly on a number our factors, as not all fish can live with one another.
Here are some of the more important things you should look for:
Adult Size and Size of Aquarium
If you only have space for a small tank, don’t buy fish that have a large adult size. Fish do not grow to the size of their tank.
The tank should be at least six times the potential length of the fish to provide plenty of swimming room although be sensible- you couldn’t keep an inch long fish in a 6 inch tank! You should roughly calculate the number of fish your tank can accommodate (check our stocking levels guide for more details) and, after carrying out a fishless cycle, stock your aquarium slowly to prevent a sudden build up of ammonia.
Be aware that some fish may require even more space if they are especially active or territorial. Many fish you see in your local shop are babies and will grow much bigger. A few will even grow to over a foot long so don’t just buy whatever takes your fancy- find out how big it will get!
Generally, the bigger the better. Larger volumes of water are safer to maintain and are much less likely to suffer from yo-yo changes. More dilution = safer water. FK usually recommends for tropicals a min of 45 litres for 1 male Betta (soft water permitting), a min of 60 litres for 1 small shoal of fish who grow to no more than 5cm but the best size starter tank is around 85 to 120 litres or more. Easy to manage and will permit a little varied stocking.
For common goldfish aim for 180 litres for the first fish with an extra 55 litres for each extra fish. The tank needs to have a minimum length of 4 feet (120cm) to allow swimming room - these fish are more suited to ponds really.
For Fancy Goldfish aim for 140 litres for the first fish with an extra 45 litres for each extra fish. The tank needs to have a minimum length of 3 feet to allow swimming room.
You may feel like a kid in a sweet shop with all the choices available but don’t be tempted to go for a pick and mix! Some fish like to live in groups, others in pairs and some like to be kept alone, i.e. the only fish of their species in a tank.
A shoal or group of fish should consist of at the very least six or more individuals but the more the merrier. If you don’t have space for at least six then don’t get any of that fish at all- without a shoal the fish can feel insecure and spend all its time hiding. It can also get sick more easily.
If a fish likes to live in a pair then this means a male and a female fish. Males tend to be prettier than females but don’t be tempted- if you get two males then they could fight and injure or even kill each other. In some circumstance it is OK to keep two males, providing they have enough space to establish their own territories.
Some fish like the Siamese fighting fish (Betta splendens) are territorial and can be aggressive towards other fish of the same species or even a similar appearance. Care should be taken that they are not kept with fish that they could attack. In some instances it is best to only keep one male of these type of fish.
If you are planning on keeping a few different species in one aquarium (known as a community) then do plenty of research into the different species you like to make sure they will get along with each other. It’s best to have fish of a similar size as very large fish may try to eat smaller ones! Ensure that all the fish have similar needs in regards to water parameters and that they will not be aggressive towards each other. Don’t forget to find out if the fish is safe with inverts (snails, shrimp etc) if you have them.
Smaller fish, in general, should not be housed with bigger fish. Try to keep the size ratios of different fish in mind. Any fish that can fit into the mouth of another fish is usually game fodder. Examples of this would be Angel fish housed with Neon, or Fancy Goldfish with Minnows. Small fish can make expensive snacks!
Some tropical fish are shoaling too, so need to be kept in groups of at least 6, but the more the better. In bigger shoals of 10 to 15 (or more, tank size permitting) they are more relaxed and behave much more naturally. Smaller groups may hide away and become timid. Some fish are pair bonders and some need to be kept alone. Some fish can be pretty territorial and if they breed, will attack anything that goes near the nest. Give territorial fish enough of a good foot print in the tank to avoid spats, bullying and fights.
If you have a planted tank then check that your new fish will not destroy your hard work!
Fish come from different habitats all over the world so some can’t live in the same type of water. Obviously it’s a bad idea to mix marine fish and freshwater fish so unfortunately little Johnny can’t have a nemo to go in with his goldfish!
It’s also not a good idea to mix tropical and coldwater fish. Make sure you know if the fish you want needs heated water or not and what temperature they prefer so you can provide it for them. If you decide to run a heater and go for tropicals - then some fish like the Minnow or Danio for example, won't be too happy in that environment as they need much cooler water. Fish have different temp ranges - even tropical fish. If you are planning on a few different types of fish for your tank, ensure they all suit the temp you are working with.
Tip: For heating, aim for 1 watt for each litre of water and then round up to the next heater size e.g. an 85 litre tank, would need a 100w heater.
Local Water pH & GH (General Hardness)
Some fish like a high pH and others like a low pH, some like soft water and some like hard water. It’s important to choose fish that like the same conditions. If you are finding it difficult to choose, look for fish that are from the same part of the world that would live together naturally. You could even set up a ‘biotope’ aquarium (containing fish and plants from a specific place).
Firstly, you will need to test your tap water for the pH. For pH, run a cup of water and leave for 24 hours. GH can be tested for immediately. Many water companies add dissolved gases and temporary buffers to alter this temporarily so it's nice for us humans to drink. After 24 hours these wear off and the pH may go up or may drop depending on the area where you live.
Stocking with fish suited to your local supply will avoid long term illness, breeding problems and often early deaths. Hard water and soft water fish should not be mixed. There are ways of course to change pH each week when you do a water change but it's far easier to cut your teeth on something more simple to begin with.
Tip: Favoured test kits for any fish keeper include the API Freshwater Master Test Kit and this company also produce a useful general hardness (GH) and carbonate hardness (KH) test kit which can be bough separately and is invaluable when choosing soft water fish.
Some fish will not accept flake or pellet food or will only accept one particular food. Make sure you know what your fish is going to eat before you buy it and that you can provide it with the right food. If the fish will be too difficult to feed then it’s a good idea to choose a different fish.
There’s an excellent feeding guide showing all sorts of food you can try, here in the general area of the FK Articles.
Some fish may be more susceptible to a particular disease, for example fish with long flowing fins may be more likely to get fin rot than fish with shorter fins. Ensure you are aware of any potential problems so that you can take steps to prevent them from happening.
When you are starting out it’s best to choose fish that are slightly hardy and easy to look after. Some fish are very delicate and sensitive to poor water conditions so they are best left to fishkeepers with a bit more experience. Other fish are difficult to feed or just need more detailed care. It’s not fair on the fish to try and keep something that you will not be able to look after. Tempting though some fish can be, you should put the needs of the fish first. A happy healthy fish is more fun to look after than a sickly fish!
Remember- fish are live animals and in most circumstances will behave as they do in the wild. They might look pretty and small but they can be territorial and act very aggressively towards each other, fight or even kill each other- they can even hurt you! So make sure you choose the right fish to avoid any future problems and you will make your life as a fishkeeper much easier.
Here’s a checklist of things to research before you buy a new fish-
The care sheets here on the left hand menu give further more detailed guidance to help you choose happy housemates for any community tank.