How many fish in a 40 gallon tank?
A 40 US gal (151 L) tank is usually 36 in (91 cm) long. By size, 39 of the 53 species in this reference fit it. The table shows how many of each the tank can carry if kept on their own, at under 80% of its bioload.
A mix shares the same capacity, so three species at a third each is the limit, not three full rows. Check a mix with the planner; it also weighs water and temperament.
Species that fit a 40 gallon tank
| Species | Adult size | Up to, kept alone | Group |
|---|---|---|---|
| Black neon tetra | 1.4 in (3.5 cm) | 55 | 10+ |
| Black skirt tetra | 3 in (7.5 cm) | 14 | 12+ |
| Cardinal tetra | 1.4 in (3.5 cm) | 55 | 10+ |
| Ember tetra | 0.8 in (2 cm) | 86 | 10+ |
| Glowlight tetra | 1.6 in (4 cm) | 46 | 6+ |
| Lemon tetra | 1.6 in (4 cm) | 41 | 10+ |
| Neon tetra | 1.2 in (3 cm) | 64 | 10+ |
| Rummy-nose tetra | 2 in (5 cm) | 34 | 10+ |
| Serpae tetra | 1.6 in (4 cm) | 41 | 12+ |
| Endler's livebearer | 1 in (2.5 cm) | 75 | |
| Guppy | 2.4 in (6 cm) | 25 | |
| Molly | 3.1 in (8 cm) | 11 | |
| Platy | 2 in (5 cm) | 28 | |
| Celestial pearl danio | 0.8 in (2.1 cm) | 89 | |
| Chili rasbora | 1.4 in (3.5 cm) | 62 | 10+ |
| Harlequin rasbora | 2 in (5 cm) | 34 | 10+ |
| White cloud mountain minnow | 1.6 in (4 cm) | 54 | 10+ |
| Zebra danio | 2 in (5 cm) | 40 | 10+ |
| Cherry barb | 2 in (5 cm) | 34 | 10+ |
| Tiger barb | 2.8 in (7 cm) | 16 | 10+ |
| Bristlenose pleco | 6 in (15 cm) | 3 | |
| Bronze corydoras | 3 in (7.5 cm) | 13 | 6+ |
| Glass catfish | 2.6 in (6.5 cm) | 26 | 6+ |
| Otocinclus | 2 in (5 cm) | 34 | 6+ |
| Panda corydoras | 2 in (5 cm) | 28 | 6+ |
| Peppered corydoras | 2.8 in (7 cm) | 15 | 5+ |
| Pygmy corydoras | 1.2 in (3 cm) | 64 | 6+ |
| Kuhli loach | 4.7 in (12 cm) | 16 | 6+ |
| Betta | 2.8 in (7 cm) | 19 | |
| Dwarf gourami | 3.7 in (9.5 cm) | 8 | |
| Paradise fish | 3.1 in (8 cm) | 14 | |
| Pearl gourami | 4.7 in (12 cm) | 5 | |
| Cockatoo dwarf cichlid | 3 in (7.5 cm) | 14 | |
| Convict cichlid | 5.9 in (15 cm) | 3 | |
| German blue ram | 1.7 in (4.2 cm) | 38 | |
| Kribensis | 4.3 in (11 cm) | 6 | |
| Cherry shrimp | 1.6 in (4 cm) | 68 | |
| Mystery snail | 2 in (5 cm) | 35 | |
| Nerite snail | 1.5 in (3.8 cm) | 52 |
Fit by size, but not in a full group
- Honey gouramiNeeds a group of 6; the tank carries 4.
Too big for a 40 gallon tank
- Congo tetraNeeds 108 L (29 US gal), at least 120 cm (47 in) long.
- SwordtailNeeds 108 L (29 US gal), at least 120 cm (47 in) long.
- Rosy barbNeeds 90 L (24 US gal), at least 100 cm (39 in) long.
- Common plecoNeeds 284 L (75 US gal), and grows to 58 cm (23 in).
- Clown loachNeeds 648 L (171 US gal), at least 180 cm (71 in) long, and grows to 40 cm (16 in).
- Yoyo loachNeeds 243 L (64 US gal), at least 120 cm (47 in) long.
- AngelfishNeeds 208 L (55 US gal), at least 100 cm (39 in) long.
- DiscusNeeds 255 L (67 US gal), at least 120 cm (47 in) long.
- OscarNeeds 540 L (143 US gal), at least 150 cm (59 in) long, and grows to 46 cm (18 in).
- Boeseman's rainbowfishNeeds 108 L (29 US gal), at least 120 cm (47 in) long.
- GoldfishNeeds 76 L (20 US gal), and grows to 48 cm (19 in).
- Red tail sharkNeeds 243 L (64 US gal), at least 120 cm (47 in) long.
- Siamese algae eaterNeeds 208 L (55 US gal).
A guide, not a guarantee. Tank sizes: 5 gal, 10 gal, 20 gal, 29 gal, 55 gal, 75 gal, 125 gal.