Least Killifish (Heterandria formosa) is a beginner-level freshwater fish that needs at least 5 gallons and 68-80°F. One of the smallest livebearers in the world, with males under an inch. Despite its name it is a livebearer, not a true killifish. It is hardy but tiny, so only keep it with very small, gentle tankmates, and add floating plants for the young.
Care facts at a glance
| Scientific name | Heterandria formosa |
|---|---|
| Family | Poeciliidae |
| Origin | Southeastern United States |
| Adult size | 1-1.5 in |
| Minimum tank | 5 gallons |
| Temperature | 68-80°F |
| pH | 6.5-8.0 |
| Temperament | Peaceful, tiny |
| Social behavior | Groups of 6+ |
| Swim level | Upper to mid |
| Difficulty | Beginner |
| Diet | Omnivore: micro pellets, crushed flakes, baby brine shrimp, small frozen foods |
| Typical lifespan | 1-2 years |
Quick tips
- Do not keep with fin-nippers or larger fish.
- Floating plants help the tiny fry survive.
- Keep a group with more females than males.
San Diego water
Tolerates San Diego's hard, alkaline tap water (pH roughly 7.6-8.6) with slow acclimation and a conditioner that handles chloramine. Learn the numbers in our San Diego tap water guide.
Before you buy
Make sure your tank is cycled (how to cycle a tank), check your numbers with the water testing guide, and use the compatibility guide to check tankmates. These are general ranges; individual fish and local water vary.
Find it at Pet Zone
Pet Zone Tropical Fish is a San Diego aquarium store with two locations. Stock changes daily, so call ahead if you are after a specific species or plant. Shop online at petzonesd.com.
4160 Convoy St, San Diego, CA 92111
(858) 987-0309
Open daily, 10am-6pm
Aquascaping, planted tanks
4266 University Ave, San Diego, CA 92105
(619) 283-1812
Closed Monday; Tue-Fri 10:30am-6pm, Sat 11am-6pm, Sun 11am-4pm
Monster fish, koi