US-gallon tank guide
What can you keep in a 40 US-gallon tank?
A 40-gallon tank adds boesemani rainbowfish, zebra loaches, sailfin mollies, odessa and gold barbs, and the clown pleco to the 29-gallon list. Bolivian rams, Congo tetras, rosy barbs and angelfish need a larger tank than this.
US gallons. About 151.4 litres, for anyone comparing with a litre tank.
Plan your 40-gallon tank
Add your species and the numbers you plan to keep. The builder starts empty, at 40 US gallons.
The main decision
Use the length and the floor for an active school and a bottom group. Do not plan angelfish for a 40 Breeder: it is too short, and a 40-gallon tank is too small.
Check the tank’s shape
In Aqueon's range the 40-gallon tank is the 40 Breeder: a published outer base of 36 3/16 × 18¼ in (91.9 × 46.4 cm) and 16 15/16 in tall. That length is only slightly over 90 cm on the outside of the glass, so measure the inside before you treat it as the 90 × 30 cm base Seriously Fish asks for zebra danios and mollies. It is also under 50 cm tall, so it is not an angelfish tank. A Bolivian ram needs more water than a 40-gallon tank, and a base of 90 × 45 cm. Other 40-gallon tanks have other shapes, so check yours. The tank builder checks volume only.
Manufacturer’s size and dimension guide →Compare species for 40 US gallons
Each species here meets this tank on volume. The smaller line is the litre minimum, rounded up into US gallons. It does not measure length or width.
Planning minimum
80 litres (21.14 US gal)
Planning minimum
40 litres (10.57 US gal)
Planning minimum
80 litres (21.14 US gal)
Planning minimum
60 litres (15.86 US gal)
Planning minimum
20 litres (5.29 US gal)
Planning minimum
60 litres (15.86 US gal)
Planning minimum
80 litres (21.14 US gal)
Planning minimum
100 litres (26.42 US gal)
Show all 74 species in this shortlist
Planning minimum
60 litres (15.86 US gal)
Planning minimum
20 litres (5.29 US gal)
- Boesemani Rainbowfish →
Fish · intermediate care · peaceful
This 40-gallon tank is large enough on volume.
Planning minimum
150 litres (39.63 US gal)
Planning minimum
80 litres (21.14 US gal)
Planning minimum
100 litres (26.42 US gal)
Planning minimum
60 litres (15.86 US gal)
- Celebes Rainbowfish →
Fish · intermediate care · peaceful
This 40-gallon tank is large enough on volume.
Planning minimum
80 litres (21.14 US gal)
- Celestial Pearl Danio →
Fish · intermediate care · peaceful
This 40-gallon tank is large enough on volume.
Planning minimum
30 litres (7.93 US gal)
Planning minimum
60 litres (15.86 US gal)
Planning minimum
20 litres (5.29 US gal)
Planning minimum
20 litres (5.29 US gal)
Planning minimum
20 litres (5.29 US gal)
Planning minimum
110 litres (29.06 US gal)
- Columbian Tetra →
Fish · beginner care · peaceful · fin-nipping risk
This 40-gallon tank is large enough on volume.
Planning minimum
80 litres (21.14 US gal)
Planning minimum
60 litres (15.86 US gal)
Planning minimum
120 litres (31.71 US gal)
Planning minimum
60 litres (15.86 US gal)
- Dwarf Neon Rainbowfish →
Fish · beginner care · peaceful
This 40-gallon tank is large enough on volume.
Planning minimum
100 litres (26.42 US gal)
Planning minimum
45 litres (11.89 US gal)
- Emerald catfish (Brochis) →
Fish · beginner care · peaceful
This 40-gallon tank is large enough on volume.
Planning minimum
120 litres (31.71 US gal)
Planning minimum
40 litres (10.57 US gal)
Planning minimum
80 litres (21.14 US gal)
Planning minimum
80 litres (21.14 US gal)
Planning minimum
60 litres (15.86 US gal)
Planning minimum
120 litres (31.71 US gal)
Planning minimum
60 litres (15.86 US gal)
Planning minimum
40 litres (10.57 US gal)
Planning minimum
60 litres (15.86 US gal)
Planning minimum
40 litres (10.57 US gal)
Planning minimum
60 litres (15.86 US gal)
Planning minimum
100 litres (26.42 US gal)
Planning minimum
70 litres (18.5 US gal)
- Lambchop / Espei rasbora →
Fish · beginner care · peaceful
This 40-gallon tank is large enough on volume.
Planning minimum
60 litres (15.86 US gal)
Planning minimum
60 litres (15.86 US gal)
- Malaysian Trumpet Snail →
Snail · beginner care · peaceful
This 40-gallon tank is large enough on volume.
Planning minimum
20 litres (5.29 US gal)
- Marbled Hatchetfish →
Fish · intermediate care · peaceful
This 40-gallon tank is large enough on volume.
Planning minimum
60 litres (15.86 US gal)
Planning minimum
80 litres (21.14 US gal)
Planning minimum
40 litres (10.57 US gal)
Planning minimum
54 litres (14.27 US gal)
Planning minimum
20 litres (5.29 US gal)
Planning minimum
120 litres (31.71 US gal)
Planning minimum
60 litres (15.86 US gal)
Planning minimum
60 litres (15.86 US gal)
Planning minimum
80 litres (21.14 US gal)
Planning minimum
100 litres (26.42 US gal)
Planning minimum
80 litres (21.14 US gal)
Planning minimum
80 litres (21.14 US gal)
Planning minimum
60 litres (15.86 US gal)
Planning minimum
30 litres (7.93 US gal)
- Rosy Tetra →
Fish · beginner care · peaceful · fin-nipping risk
This 40-gallon tank is large enough on volume.
Planning minimum
80 litres (21.14 US gal)
Planning minimum
80 litres (21.14 US gal)
Planning minimum
120 litres (31.71 US gal)
- Salt and pepper cory / dwarf cory →
Fish · intermediate care · peaceful
This 40-gallon tank is large enough on volume.
Planning minimum
60 litres (15.86 US gal)
Planning minimum
100 litres (26.42 US gal)
- Silver Tip Tetra →
Fish · beginner care · peaceful · fin-nipping risk
This 40-gallon tank is large enough on volume.
Planning minimum
60 litres (15.86 US gal)
- Sparkling Gourami →
Fish · intermediate care · peaceful
This 40-gallon tank is large enough on volume.
Planning minimum
40 litres (10.57 US gal)
- Sterba's Corydoras →
Fish · intermediate care · peaceful
This 40-gallon tank is large enough on volume.
Planning minimum
100 litres (26.42 US gal)
Planning minimum
80 litres (21.14 US gal)
- Threadfin rainbowfish →
Fish · intermediate care · peaceful
This 40-gallon tank is large enough on volume.
Planning minimum
60 litres (15.86 US gal)
Planning minimum
100 litres (26.42 US gal)
- Twig / whiptail catfish →
Fish · intermediate care · peaceful
This 40-gallon tank is large enough on volume.
Planning minimum
150 litres (39.63 US gal)
- Upside-down Catfish →
Fish · intermediate care · peaceful
This 40-gallon tank is large enough on volume.
Planning minimum
100 litres (26.42 US gal)
- White Cloud Mountain Minnow →
Fish · beginner care · peaceful
This 40-gallon tank is large enough on volume.
Planning minimum
40 litres (10.57 US gal)
Planning minimum
60 litres (15.86 US gal)
Planning minimum
81 litres (21.4 US gal)
Planning minimum
120 litres (31.71 US gal)
Plans worth checking on their own
Each idea is a separate plan, not a list to combine. Check the species and the numbers in the tank builder before you buy.
Zebra danios with room to run
Eight or more zebra danios. A 40-gallon tank is large enough on volume. Seriously Fish asks for a group of at least 8 to 10 and a base of about 90 × 30 cm. Aqueon's 40 Breeder has a published outer base of 91.9 × 46.4 cm. Measure the inside length before you treat that as the base. They are fast swimmers, so keep slow or long-finned fish out.
Boesemani rainbowfish and zebra loaches
Six boesemani rainbowfish with six zebra loaches. The rainbowfish stay in midwater and the loaches on the bottom. Rainbowfish need about pH 7–8, so keep soft-water fish out. A 40-gallon tank is large enough for both on volume.
Other species need a closer look
These meet the volume minimum too, but fall outside the shortlist above because of their care needs, size or behaviour. A volume match does not make them suitable tank mates.
- African freshwater butterflyfish →
Fish · intermediate care · peaceful · fin-nipping risk · may eat smaller animals
This 40-gallon tank is large enough on volume.
Planning minimum
150 litres (39.63 US gal)
- Agassiz’s dwarf cichlid →
Fish · intermediate care · semi-aggressive · fin-nipping risk · may eat smaller animals
This 40-gallon tank is large enough on volume.
Planning minimum
80 litres (21.14 US gal)
- American Flagfish →
Fish · intermediate care · semi-aggressive · fin-nipping risk
This 40-gallon tank is large enough on volume.
Planning minimum
60 litres (15.86 US gal)
- Apistogramma Borellii →
Fish · intermediate care · semi-aggressive
This 40-gallon tank is large enough on volume.
Planning minimum
80 litres (21.14 US gal)
See all 26 species and their requirements
- Apistogramma Macmasteri →
Fish · intermediate care · semi-aggressive
This 40-gallon tank is large enough on volume.
Planning minimum
100 litres (26.42 US gal)
- Apistogramma Trifasciata →
Fish · intermediate care · semi-aggressive
This 40-gallon tank is large enough on volume.
Planning minimum
80 litres (21.14 US gal)
- Assassin Snail →
Snail · beginner care · peaceful · may eat smaller animals
This 40-gallon tank is large enough on volume.
Planning minimum
30 litres (7.93 US gal)
- Brown / hockey-stick pencilfish →
Fish · intermediate care · peaceful · may eat smaller animals
This 40-gallon tank is large enough on volume.
Planning minimum
100 litres (26.42 US gal)
- Checkerboard cichlid →
Fish · intermediate care · peaceful · may eat smaller animals
This 40-gallon tank is large enough on volume.
Planning minimum
100 litres (26.42 US gal)
- Chocolate gourami →
Fish · advanced care · peaceful · may eat smaller animals
This 40-gallon tank is large enough on volume.
Planning minimum
80 litres (21.14 US gal)
- Cockatoo / crested Apistogramma →
Fish · intermediate care · semi-aggressive · fin-nipping risk · may eat smaller animals
This 40-gallon tank is large enough on volume.
Planning minimum
100 litres (26.42 US gal)
- Croaking gourami →
Fish · intermediate care · peaceful · may eat smaller animals
This 40-gallon tank is large enough on volume.
Planning minimum
80 litres (21.14 US gal)
- Dojo / weather loach →
Fish · intermediate care · peaceful · may eat smaller animals
This 40-gallon tank is large enough on volume.
Planning minimum
150 litres (39.63 US gal)
- Dwarf pencilfish →
Fish · intermediate care · peaceful · may eat smaller animals
This 40-gallon tank is large enough on volume.
Planning minimum
60 litres (15.86 US gal)
- Electric Blue Acara →
Fish · intermediate care · semi-aggressive · may eat smaller animals
This 40-gallon tank is large enough on volume.
Planning minimum
150 litres (39.63 US gal)
- Ghost Shrimp →
Shrimp · beginner care · semi-aggressive · may eat smaller animals
This 40-gallon tank is large enough on volume.
Planning minimum
40 litres (10.57 US gal)
- Golden / Beckford's pencilfish →
Fish · intermediate care · peaceful · may eat smaller animals
This 40-gallon tank is large enough on volume.
Planning minimum
80 litres (21.14 US gal)
- Golden dwarf cichlid (Nannacara) →
Fish · intermediate care · peaceful · may eat smaller animals
This 40-gallon tank is large enough on volume.
Planning minimum
50 litres (13.21 US gal)
- Golden Wonder Killifish →
Fish · intermediate care · semi-aggressive · may eat smaller animals
This 40-gallon tank is large enough on volume.
Planning minimum
80 litres (21.14 US gal)
Planning minimum
100 litres (26.42 US gal)
- Opaline gourami →
Fish · intermediate care · semi-aggressive · fin-nipping risk · may eat smaller animals
This 40-gallon tank is large enough on volume.
Planning minimum
150 litres (39.63 US gal)
- Paradise fish →
Fish · intermediate care · semi-aggressive · fin-nipping risk · may eat smaller animals
This 40-gallon tank is large enough on volume.
Planning minimum
120 litres (31.71 US gal)
- Pea Puffer →
Fish · intermediate care · semi-aggressive · fin-nipping risk · may eat smaller animals
This 40-gallon tank is large enough on volume.
Planning minimum
40 litres (10.57 US gal)
- Serpae Tetra →
Fish · intermediate care · semi-aggressive · fin-nipping risk
This 40-gallon tank is large enough on volume.
Planning minimum
100 litres (26.42 US gal)
- Splash tetra →
Fish · advanced care · peaceful · may eat smaller animals
This 40-gallon tank is large enough on volume.
Planning minimum
80 litres (21.14 US gal)
- Tiger Barb →
Fish · intermediate care · semi-aggressive · fin-nipping risk
This 40-gallon tank is large enough on volume.
Planning minimum
80 litres (21.14 US gal)
Species that need a larger tank
A 40-gallon tank is too small for Bolivian rams, Congo tetras, rosy barbs, moonlight gouramis, angelfish and discus.
Each of these needs a larger tank than 40 US gallons. Buying a small juvenile does not change that.
- Bolivian Ram →
Needs a larger tank than 40 US gallons.
Planning minimum 180 litres (47.56 US gal).
- Congo Tetra →
Needs a larger tank than 40 US gallons.
Planning minimum 180 litres (47.56 US gal).
- Moonlight gourami →
Needs a larger tank than 40 US gallons.
Planning minimum 180 litres (47.56 US gal).
- Rosy Barb →
Needs a larger tank than 40 US gallons.
Planning minimum 180 litres (47.56 US gal).
- African Cichlid →
Needs a larger tank than 40 US gallons.
Planning minimum 200 litres (52.84 US gal).
- Angelfish →
Needs a larger tank than 40 US gallons.
Planning minimum 200 litres (52.84 US gal).
- Convict cichlid →
Needs a larger tank than 40 US gallons.
Planning minimum 200 litres (52.84 US gal).
- Cuckoo / petricola catfish →
Needs a larger tank than 40 US gallons.
Planning minimum 200 litres (52.84 US gal).
- Discus →
Needs a larger tank than 40 US gallons.
Planning minimum 200 litres (52.84 US gal).
Common mistakes at this size
- Planning angelfish for a 40 Breeder. They need a larger tank, and a tank at least 50 cm tall. The 40 Breeder's published height is 16 15/16 in.
- Buying a Bolivian ram because the 40 Breeder's base is close to 90 × 45 cm. A ram needs more water than a 40-gallon tank holds.
Have a few species in mind?
Check them together, with the numbers you plan to keep. The builder checks group sizes, water ranges and every pair, with a stocking estimate.
Build a 40 US-gallon planExplore another tank size
The gallon figure beside a planning minimum is the litre figure, rounded up. A tank at that gallon figure meets the litre minimum. It is not a separate biological limit. The lists use the tank’s nominal volume. Read how the checks work and their limitations.