What fish can I keep in a 40 gallon tank?

A 40 gallon aquarium can house any species with a minimum tank of 40 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 40 gallon tank?

Stocking density depends on body mass, not just count. As a rough guideline, a peaceful community tank can hold about 36″ of slender fish, or roughly 20″ of deep-bodied cichlids. Use the tank builder for a species-aware bioload check.

Stocking Ideas

40 Gallon Fish Tank

Every stocking below fits a 40 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 40 gallons or less, grouped by water type.

Curated stockings for 40 gallons

Freshwater presets

Classic Community

The everyone-knows-it 40 gallon

40gal · 3 species · 18 fish

Schoolers Showcase

Two tight schools and a gentle anchor

40gal · 3 species · 15 fish

Cardinal Showcase

A serious cardinal school with a honey gourami anchor

30gal · 2 species · 13 fish

Bolivian Cichlid Tank

Dwarf cichlid with a school of cherry barbs

30gal · 3 species · 13 fish

30g Apisto Pair

Dwarf cichlid pair with a tetra dither

30gal · 3 species · 15 fish

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

Brackish presets

30g Brackish Figure 8 Tank

Three Figure 8 puffers in their actual habitat

30gal · 2 species · 7 fish

Saltwater presets

40g Mixed Reef

Five families, no overlap, no fights

40gal · 5 species · 5 fish

40g FOWLR With Bite

Centropyge color in a coral-free tank

40gal · 4 species · 4 fish

40g Mixed LPS Garden

Fleshy LPS in every colour, no Euphyllia warfare

40gal · 3 species · 3 fish

FOWLR Starter

A first saltwater build that doesn't bite back

30gal · 3 species · 7 fish

30g Beginner Reef

A first reef with corals that forgive mistakes

30gal · 3 species · 3 fish

30g Anemone & Clownfish

The iconic pairing, done safely

30gal · 2 species · 2 fish

20g Nano Reef

Single-fish reef that fits on a desk

20gal · 2 species · 2 fish

Species that fit a 40 gallon tank

Fitting means the species' minimum tank size is at or below 40 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.