Best freshwater fish: species guides for every tank

01

How to choose the best freshwater fish for your tank

Most stocking problems start in the store, when a fish is chosen for its color before anyone checks its adult size. A better order is simple: start from your tank, then your water, then temperament. The tank’s volume and footprint set the limit on adult size and on how many fish you can keep. Your tap water decides whether soft-water fish like ember tetras or hard-water fish like guppies and platies will settle in with the least effort. Temperament decides which species can share the tank.

Before you buy any fish, the tank needs to be cycled so beneficial bacteria can break down waste. If that step is new to you, read how to cycle a fish tank first, and test your water with a reliable aquarium test kit so you know your pH and hardness.

• Adult size: always plan for the adult fish, not the juvenile in the bag
• Minimum tank: our guides give gallons and litres, plus the footprint that matters for active swimmers
• Water: temperature, pH, GH and KH ranges for each species
• Social needs: alone, pairs, or groups of 6 to 10 or more
• Temperament: peaceful, semi-aggressive, fin-nipper or predator

02

Where to start if you are new

If this is your first aquarium, start with our list of the best beginner fish. Those species forgive small swings in temperature and water quality while you learn. A 20-gallon (75 L) tank is easier to keep stable than a 5-gallon, and our beginner aquarium guide walks through the equipment and the first weeks step by step.

Popular first choices include the guppy, corydoras catfish and the harlequin rasbora. A betta fish is a good pick for a single 5 to 10 gallon tank, as long as it gets a heater and gentle filtration.

03

Fish by tank size

Small tanks are not easier, they are less forgiving. For 5 to 10 gallons, stick to true nano fish such as ember tetras or celestial pearl danios. For a 20-gallon or larger community, you can add a bottom-dweller group, a mid-water school and one centerpiece fish. Our stocking pages give sample communities with fish counts: best fish for a 10 gallon tank, 20 gallon and 55 gallon.

04

Freshwater fish groups at a glance

Most popular aquarium fish fall into a few families. Knowing the family tells you a lot about care before you even read the species guide.

05

Compatibility and health

Mixing species is where most losses happen. Check the tank mates guides before you combine a betta, angelfish or cichlid with anything else. When a fish looks unwell, our troubleshooting section covers ich, fin rot, swim bladder problems and ammonia poisoning, and lists the symptoms to compare against.