How To Choose Fish For A Freshwater Aquarium

Choosing fish for your freshwater aquarium can be difficult. As a rule, you should not judge a fish by its appearance and you should never choose a fish just because you like it. This article is intended to help you find the right fish for your freshwater aquarium.

  1. The size of your aquarium is a key factor in finding the right fish. Some fish need a lot of space or should be kept in a shoal that may be too big for your tank. Some freshwater fish can grow more than 30cm long! You must start with the size of the adult fish. (e.g. clownfish!) Your aquarium may be too small for fish that need their own territory so as not to get in each other’s enclosures. Goldfish are very unclean and take a lot of work. These fish need a better filtration system and more space compared to cleaner fish that can be kept in larger numbers.
  2. It’s also a good idea to pick up some books or just google “freshwater fish species”. Once you have decided on a fish, you can check whether it is suitable for your aquarium or adapt your aquarium to the fish.
  3. You have to find out how aggressive the fish you like is. Aggressive fish will fight with each other. Many fish are aggressive towards their own species or male fish of their species. Some fish are incredibly social and need companions.
  4. If you buy a female and a male fish they may breed, and find out if they are aggressive toward other fish. They should have a plan for what to do with the baby fish. Find out about breeding behavior before you buy and learn how to recognize their dimorphism (the difference between the sexes). 
  5. Find out what this fish is eating, the fish food might be hard to find and the fish might starve. Some fish only eat live food, such as knife fish. Other fish eat their own kind. 
  6. Find out how difficult or easy it is to hold the fish. By that I mean consider how much time you have for your fish and how much work you want to put on your shoulders. No fish is difficult if you know what you are dealing with. An example of a “difficult” fish is the discus fish. This fish likes clean water, meaning the water should be changed several times a week. They also get sick more often than other fish. Think about how much time you have and buy the appropriate fish. 
  7. Next, find out where to find the fish best. If the fish is difficult to find, consider buying one that is more common. Some fish are also very expensive and may be too expensive to make you want to buy cheaper fish. In any case, pay attention to QUALITY! 
  8. If you are planning a community aquarium, make sure the species you want to keep together are compatible and have similar needs. For example, goldfish are cold-water fish and bettas are tropical fish that cannot be kept in the same tank (although both types of fish are classified as ‘easy’ fish, they are still very different!). 
  9. If you are having trouble figuring out which fish can be kept together, you should post to an online fish forum and ask for advice. The people on these forums are helpful and very knowledgeable!


  • Do enough research before you buy your fish.
  • Make sure your water parameter is good for the fish, if not good, wait until you have your fish.
  • If the fish are delivered by post, be sure to acclimatize the fish properly.


  • Allow the fish to acclimate before placing them in the aquarium.
  • Don’t put a sick fish in an aquarium, or a healthy fish in a sick aquarium.
  • Don’t listen to sellers. They are just trying to sell you the fish and they don’t care if the fish fits in your tank or not. In most cases, sellers don’t know enough about fish either.
Mary Allen

Written by Mary Allen

Hello, I'm Mary! I've cared for many pet species including dogs, cats, guinea pigs, fish, and bearded dragons. I also have ten pets of my own currently. I've written many topics in this space including how-tos, informational articles, care guides, breed guides, and more.

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