Best fish for a 40 gallon tank (and how many)

Best fish for a 40 gallon tank

In order of how well they suit a 40 gallon tank. "Up to" is the most of that one species the tank holds on its own; mixing species splits it.

1. 1.Rummynose tetra Petitella rhodostoma (most sold are P. bleheri)

   2" adult · groups of 10+ · 75–81 °F · pH 5.5–7 · up to 25 in a 40 gallon

   Seriously Fish says keep 10 or more, in a tank at least 90 cm (36 in) long, which the breeder just meets. Most fish sold as rummy-noses are now classified as Petitella bleheri.^{[5, 6]}

2. 2.Pearl gourami Trichopodus leerii

   5" adult · one is fine · 75–86 °F · pH 5.5–8 · up to 6 in a 40 gallon

   One of the most peaceful gouramis, on a 90 × 30 cm base. Males are territorial with each other, so keep one.^[7]

3. 3.Lemon tetra Hyphessobrycon pulchripinnis

   1.6" adult · groups of 8+ · 68–82 °F · pH 5–7.5 · up to 20 in a 40 gallon

   A very peaceful tetra; Seriously Fish recommends a mixed group of 8–10 and an 80 × 30 cm base.^[8]

4. 4.Kribensis Pelvicachromis pulcher

   3.9" adult · groups of 2+ · 75–81 °F · pH 5–7.5 · up to 8 in a 40 gallon

   One pair fits the breeder's depth: Seriously Fish's base for a single pair is 60 × 37.5 cm. Good community fish until they breed, then very territorial.^[2]

5. 5.Bolivian ram Mikrogeophagus altispinosus

   3.5" adult · one is fine · 75–82 °F · pH 6–7.5 · up to 9 in a 40 gallon

   Kept singly or as a bonded pair on a 90 × 45 cm base; Seriously Fish says it needs pristine water.^[1]

6. 6.Harlequin rasbora Trigonostigma heteromorpha

   1.75" adult · groups of 8+ · 73–81 °F · pH 6–7.5 · up to 28 in a 40 gallon

   Seriously Fish says harlequins should be kept in a group of at least 8–10.^[9]

7. 7.Corydoras Corydoras spp.

   3" adult · groups of 6+ · 72–78 °F · pH 6.5–7.5 · up to 11 in a 40 gallon

   A group of six or more bronze or peppered corys over sand.^[10]

8. 8.Honey gourami Trichogaster chuna

   2" adult · groups of 2+ · 72–81 °F · pH 6–7.5 · up to 16 in a 40 gallon

   Seriously Fish's notes recommend 4–6; a group of four adds a calm centerpiece without crowding.^[11]

9. 9.Cherry barb Puntius titteya

   2" adult · groups of 6+ · 68–81 °F · pH 6–8 · up to 25 in a 40 gallon

   A peaceful barb kept in groups of at least 6–10.^[12]

10. 10.Dwarf neon rainbowfish Melanotaenia praecox

    3.1" adult · groups of 6+ · 73–82 °F · pH 6.8–7.5 · up to 10 in a 40 gallon

    A small, peaceful rainbowfish that does far better in a shoal of at least 6–8.^[13]

11. 11.Odessa barb Pethia padamya

    1.8" adult · groups of 8+ · 61–77 °F · pH 6.5–8.5 · up to 18 in a 40 gallon

    A very peaceful barb for cooler water; keep a mixed group of 8–10.^[14]

Shrimp and snails for a 40 gallon tank

Listed separately: the fish bio-load budget below doesn't describe invertebrates, so they aren't counted in it.

• Amano shrimp Caridina multidentata

  Strong algae eaters that don't need a group; keep a tight lid.^[15]

• Nerite snail Neritidae (e.g. Vittina natalensis)

  Grazes algae off glass and decor.^[16]

• Mystery snail Pomacea diffusa

  Needs hard water, with a pH of at least 7.2 per Aquarium Co-Op.^[17]

How many of each fish fit in a 40 gallon tank

A 40 gallon breeder (36 × 18 × 16 in) holds about 40 gallons of water once you take off the glass. Our stocking calculator budgets that water by adult size and body shape: about 0.8 gallons per inch of slim fish (tetras, rasboras), 1.2 for medium-bodied fish (guppies, corys) and 2 for heavy, messy fish (goldfish, plecos). That works out to roughly 50 inches of small, slim adult fish in total. It is an upper limit, not a target: filtration, plants, territory and how often you change water all move it.

Stocking ideas for a 40 gallon tank

Stocking plans that fit the tank's bio-load budget, with a temperature and pH range that suits everything in them.

Fish to avoid in a 40 gallon tank

• Angelfish · needs 75+ gallons, 40 in long, 16 in front to back

  Seriously Fish's smallest tank for angelfish is 100 × 40 × 50 cm. The breeder is too short at 36 inches, the 40 long too narrow at 12 inches front to back, and both are only 16 inches tall.^[21]

• Swordtail · needs 33+ gallons, 48 in long

  Needs a 120 × 30 cm footprint; the 40 long meets it, the breeder doesn't.^[3]

• Boeseman's rainbowfish · needs 33+ gallons, 48 in long

  Seriously Fish's minimum is 120 × 30 cm, a 4-foot tank such as the 40 long.^[4]

• Giant danio · needs 60+ gallons, 48 in long, 18 in front to back

  Seriously Fish's minimum base is 120 × 45 cm, longer than a breeder and deeper than a 40 long.^[22]

• Common pleco · needs 125+ gallons, 72 in long

  Reaches about 20 inches and, per ScotCat, needs a 6-foot tank.^[23]

40 gallon tank FAQ

How many fish can you put in a 40 gallon tank?

Roughly 50 inches of small, slim adult fish by our bio-load method: for example 10 rummy-nose tetras, a pearl gourami and 10 pygmy corydoras, or a kribensis pair with 10 lemon tetras and a bristlenose pleco. Group sizes still apply.^{[5, 7, 2]}

Is a 40 breeder or a 40 long better for fish?

The breeder holds more water (about 40 gallons against 35) and its 18-inch depth suits cichlid pairs: Seriously Fish's base for a Bolivian ram is 90 × 45 cm. The long's 48-inch length suits swordtails and Boeseman's rainbowfish, whose bases are 120 cm long.^{[1, 3, 4]}

Can angelfish live in a 40 gallon tank?

Seriously Fish's smallest recommended tank for angelfish is 100 × 40 × 50 cm (about 40 × 16 × 20 in), which neither 40 gallon shape meets. A 75 does; a 60 gallon breeder has the footprint, but at 16 inches tall it falls short of the 50 cm height.^[21]

Can tiger barbs go in a 40 gallon tank?

Yes: Seriously Fish's base is 80 × 30 cm. It says their nipping is worst in small groups or cramped tanks, so keep a proper group and no long-finned fish.^[24]

How many neon tetras can you put in a 40 gallon tank?

Up to about 33 on their own by bio-load, and at least 8–10 so they school.^[25]