What fish can I keep in a 20 gallon tank?

A 20 gallon aquarium can house any species with a minimum tank of 20 gallons or less. Every fitting species is listed on this page, grouped by water type (freshwater, brackish, saltwater) and ranked by keeper interest.

How many fish is too many in a 20 gallon tank?

Stocking density depends on body mass, not just count. As a rough guideline, a peaceful community tank can hold about 18″ of slender fish, or roughly 10″ of deep-bodied cichlids. Use the tank builder for a species-aware bioload check.

Stocking Ideas

20 Gallon Fish Tank

Every stocking below fits a 20 gallon aquarium and passes the compatibility engine. Curated presets are hand-designed community tanks you can load as a starting point; the species lists show every fish whose minimum tank size is 20 gallons or less, grouped by water type.

Curated stockings for 20 gallons

Freshwater presets

Betta & Buddies

Centerpiece male betta with a peaceful schooler

15gal · 2 species · 7 fish

Pea Puffer Species Tank

Four mischievous puffers, no roommates

10gal · 1 species · 4 fish

Saltwater presets

20g Nano Reef

Single-fish reef that fits on a desk

20gal · 2 species · 2 fish

Species that fit a 20 gallon tank

Fitting means the species' minimum tank size is at or below 20 gallons. Schooling species are listed first since they tend to be the most visually rewarding stocking. Tap any card for the full care profile and its compatible tank mates.