Fish guides
What tank each popular fish needs, how many fit in each standard size, and where the care sources disagree.
How these guides work
Each fish guide starts from the minimum tank footprint given in the species’ Seriously Fish profile, and shows which standard tanks meet it. Where other respected sources give different advice, such as Aquarium Co-Op’s volume rules for bettas and goldfish, both are shown side by side so you can see where they agree and where they do not.
The “how many fit” tables come from the same model as the stocking calculator, and count each fish on its own. A real community mixes species, so plan the full list in the calculator before you buy.
How many fish fit
- How many fish in a 5 gallon tank A betta, or a few tiny fish.
- How many fish in a 10 gallon tank About 8 to 10 small fish.
- How many fish in a 20 gallon tank Around 15 small fish, in the right mix.
- How many fish in a 29 gallon tank A school of 12, plus a few bottom fish.
- How many fish in a 40 gallon tank Room for a pair of dwarf cichlids with a school.
- How many fish in a 55 gallon tank Big schools, or a first cichlid tank.
- How many fish in a 75 gallon tank Angelfish, discus or a rainbowfish community.
Check your own mix
The stocking calculator covers 100 freshwater species. Add your tank and fish to see how full it is, whether the fish suit each other, and whether the tank meets each species’ recommended footprint.