Number of Fish Per Gallon
How many fish should be there in a gallon of water?
About 1 adult fish of 1 inch of size.
When stocking an aquarium, a general rule of thumb is to have 1 gallon of water for every inch of adult fish. This can be traced to the book ‘Å“Tropical Aquarium Fish’ by U. Baensch published in 1983. This is just a general rule however, and other factors beside size should be taken into consideration for the living space needed by fish, such as activity level, growth, and so on.