Least killifish care
Heterandria formosa · Southeastern United States, from North Carolina to Florida and Louisiana
Least killifish are not killifish but tiny livebearers, among the smallest fish in the world and native to the southeastern United States.
- Tank size
- 5 US gal or larger
- Temperature
- 64 to 80 °F (18 to 27 °C)
- Group size
- 6 or more
- Temperament
- Peaceful
- Adult size
- 1.2 in (females; males about 0.8 in)
- pH
- 7 to 8
- Hardness (GH)
- 5 to 20 dGH
- Lifespan
- 2 to 3 years
- Diet
- Micropredator
- Care level
- Easy
In a 5 gallon: Aqueon 5½
16 3/16 × 8⅜ × 10½ in outsideHow to keep least killifish
Least killifish are not killifish but tiny livebearers, among the smallest fish in the world and native to the southeastern United States. Keep a group of six or more, with more females than males, in a planted 5 gallon or larger tank at 64 to 80 °F; most homes need no heater for them.
Diet: Micropredator: crushed flakes, baby brine shrimp, micro foods. Fish food types compared · how often to feed.
Where they swim: Middle of the tank.
Least killifish tank mates
Share the temperature and water, and neither side eats, nips or bullies the other. Check the full group in the stocking checker.
Crystal red shrimp
1.2 in · 10+ gal · 62–76 °F
Malaysian trumpet snail
1.2 in · 5+ gal · 64–86 °F
DrawingRed neon blue-eye
1.2 in · 10+ gal · 74–82 °F
Salt-and-pepper corydoras
1 in · 10+ gal · 72–79 °F
Zebra nerite snail
1 in · 5+ gal · 70–80 °F
Assassin snail
1 in · 5+ gal · 72–80 °F
Ramshorn snail
1 in · 5+ gal · 64–82 °F
Thai micro crab
1 in · 5+ gal · 70–82 °F
Keep apart
Pea puffer: Pea puffers belong in a tank of their own.
Everglades pygmy sunfish: Everglades pygmy sunfish belong in a tank of their own.
Angelfish: Adult angelfish eat fish under about 2 in; least killifish grow to 1.2 in.
Discus: No shared temperature: least killifish need 64 to 80 °F, discus 82 to 88 °F.
Blood parrot cichlid: Adult blood parrot cichlids eat fish under about 2 in; least killifish grow to 1.2 in.
Oscar: Adult oscars eat fish under about 4 in; least killifish grow to 1.2 in.
What a least killifish tank needs
A tank of 5 US gallons or more (such as the 5 gallon: Aqueon 5½) with a cover, and the equipment below. Least killifish are comfortable at room temperature, so a heater is optional in a normal home.
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Aquarium Co-Op Easy Flow Sponge Filter, Nano
A sponge filter gives gentle flow and cannot pull in small fish. It runs from an air pump, with airline tubing and a check valve, all sold separately.
Aqueon QuietFlow Internal Power Filter up to 5 gal
Rated by the maker for up to 5 US gal, which covers a 5 gallon least killifish tank without being built for a far bigger one.
hygger Hang-on-back Canister Filter 5W
Rated by the maker for up to 10 US gal, which covers a 5 gallon least killifish tank without being built for a far bigger one. Its surface skimmer can pull in small fish: cover it with sponge or mesh, as hygger advises.
API Freshwater Master Test Kit
Tests ammonia, nitrite, nitrate and pH, the readings that matter most before and after adding least killifish.
Seachem Prime 100 mL
Removes chlorine and chloramine from tap water at every water change.
Fluval Edge Thermometer
Shows the water temperature at a glance, so you know it stays within 64 to 80 °F.
More choices, each with the reason it is in or out: Filters for a 5 gallon tank. We don’t list fish food: any good brand of the foods under Diet will do. Plan the whole tank's equipment →
Common least killifish problems
- Almost any larger fish eats them; keep them alone or with shrimp and snails.
- Their tiny mouths need crushed flakes and baby brine shrimp.
Test the water first whenever fish look unwell: see what your readings mean, then match the symptom. For disease, a vet who treats fish can diagnose it and advise treatment.
More to compare
Sources
Name, origin and adult size checked against Wikipedia: Heterandria formosa. Temperature, pH, hardness, group size, lifespan and minimum tank size are common hobby guidance, not figures from that article. Ranges are the range the species tolerates; aim for the middle. Minimum tank sizes are for an adult group. Drawings are our own; photo credits follow.
Photo credits
Real photographs from Wikimedia Commons, resized and cropped to fit; each is used under the license named.
- Least killifish Brian Gratwicke, CC BY 2.0, via Wikimedia Commons
- Crystal red shrimp DirkBlankenhaus, CC BY-SA 3.0, via Wikimedia Commons
- Malaysian trumpet snail Buchling, CC BY-SA 3.0, via Wikimedia Commons
- Salt-and-pepper corydoras D.W., CC0, via Wikimedia Commons
- Zebra nerite snail TheJammingYam, CC BY-SA 3.0, via Wikimedia Commons
- Assassin snail Steffi Klee, CC BY-SA 3.0, via Wikimedia Commons
- Ramshorn snail Dat doris, CC BY-SA 4.0, via Wikimedia Commons
- Thai micro crab Sean Murray, CC BY-SA 2.0, via Wikimedia Commons
- Pea puffer Beta Mahatvaraj, CC BY-SA 4.0, via Wikimedia Commons
- Everglades pygmy sunfish Brian Gratwicke, CC BY 2.0, via Wikimedia Commons
- Angelfish Citron, CC BY-SA 3.0, via Wikimedia Commons
- Discus Patrick Farrelly, Public domain, via Wikimedia Commons
- Blood parrot cichlid Citron, CC BY-SA 3.0, via Wikimedia Commons
- Oscar H. Zell, CC BY-SA 3.0, via Wikimedia Commons
- Guppy Marrabbio2, CC BY-SA 3.0, via Wikimedia Commons
- Endler's livebearer Dgrummon, CC BY-SA 4.0, via Wikimedia Commons
- Molly LPA74, CC BY-SA 4.0, via Wikimedia Commons
- Platy Monika Korzeniec, CC BY-SA 3.0, via Wikimedia Commons
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