How Many Fish Can I Keep in My Aquarium?

Having an aquarium can be a satisfying and fun adventure for the whole family. In order to make sure that your fish are happy and healthy, you need to know how many fish is too many in one aquarium.

  1. Size of Tank

    • The size of the tank determines the number of fish it houses. The general rule is that you should never have more than one fish per gallon of water. However, there may be times when you have more or fewer fish, depending on the situation.

    Size of Fish

    • The size of fish is an important factor. You cannot keep 10 koi that are all longer than 3 inches in a 10-gallon tank; they are much too big. Fish will not grow any larger than the oxygen in the tank allows. If you begin with 10 fish that are less than 1 inch long in a 10-gallon tank, they will only grow to a size that can be supported by the tank and its oxygen supply. If your fish are longer than 3 or 4 inches, make sure there is at least 2 gallons of water per fish, if not more.

    Schooling or Non Schooling

    • Some fish, like tetras and silver barbs, are schooling fish. You should buy them in groups of 5 or more. They will not be happy and healthy without a school. For a 10-gallon tank, consider getting two different schools of fish. For larger tanks, try to stick to the same idea of one fish per gallon of water, but be mindful of which type of fish needs to be in schools.

    Loner Fish

    • Some fish cannot live in a tank with other fish. Beta fish will attack and kill some types of fish and will leave others alone. They will attack each other, but will be fine with gold barbs. Oscar fish will attack smaller fish and will end up alone in a tank if they can manage it. Bottom line: Ten loner fish together in a 10-gallon tank will lead to one fish.

    Considerations

    • A well-balanced tank is important. For almost all fresh-water tanks, a plecostomus is going to keep algae from growing in the tank and won't bother other fish. Keep your schools balanced with roughly the same number of fish in each group. Make sure that you have the right oxygen system for your tank, because the greater number of fish, the more oxygen you are going to need.