How many fish can I keep in an aquarium?

* The amount of fish you may keep is based on the surface area of the aquarium and whether it is freshwater or marine fish tank.

In a freshwater aquarium, you may usually keep one inch of fish per gallon of water.

In marine tanks, which have much less dissolved oxygen per volume, the rule is three inches of fish per square foot of surface area.

In tall narrow tanks, the number of fish is reduced.