How Many Fish Can Be in a 37 Gallon Aquarium?

There are several ways to figure out how many fish can go into an aquarium. There are a lot of things to take into consideration, like the shape of the aquarium, how many decorations you want to put into it, filtration and mature size of the fish you choose.

  1. One Inch per Gallon Rule

    • For freshwater fish, some people will use the 1 inch of fish per gallon of water rule. This can work well if you are using small, quiet community fish like neon tetras, white clouds and other small schooling fish.

    Saltwater

    • Saltwater is denser than fresh water, so you can't use the 1 inch per gallon rule. Instead, saltwater fanciers tend to follow 3 inches of fish per 1 square foot of surface area rule. Figure the area of your surface water and divide it by three. This will give you the number of fish you can include.

    Compatibility

    • Some fish are more aggressive or produce more waste. These fish require more space per fish. For example, some people suggest 5 gallons per goldfish while some suggest 10 gallons per goldfish. Aggressive fish like Oscars and Jack Dempseys can sometimes require a whole tank to themselves.