What is the maximum proportion of fish per liter in an aquarium?
How many fish can I have per liter in my aquarium, or how much water should I have for each fish?
When determining the capacity of an aquarium, it is common to look at total fish length rather than number of fish. The idea is that bigger fish need more room. The rule-of-thumb I've always used for freshwater tropical fish is 1 inch of fish length per gallon of water (or about 25 mm of fish length per 4 liters). However, this can vary greatly based on the species of fish. Some fish need more room than others.