Least Killifish
Heterandria formosa
Minimum Tank
5 Gallons
Adult Size
1 inches
Temperature
66-75°F (19-24°C)
pH Range
7.0-8.0
Lifespan
3 years
School Size
8+ fish
About Least Killifish
The least killifish holds the distinction of being one of the smallest vertebrates in the world, with females reaching about one inch and males barely half an inch. Despite its name, it is not a true killifish but a livebearer belonging to the family Poeciliidae. Native to the southeastern United States, from South Carolina to Louisiana, it inhabits shallow, vegetated margins of ponds, swamps, and slow streams. Least killifish are inconspicuous in appearance, with olive to tan bodies and a subtle dark lateral stripe, but their tiny size and peaceful nature make them fascinating subjects for dedicated nano tank enthusiasts. Females give birth to just 2-5 fully formed fry at a time, one of the smallest broods of any livebearer.
Care Requirements
Tank Setup
- • Minimum 5-gallon tank required
- • Temperature: 66-75°F (19-24°C)
- • pH: 7.0 - 8.0
- • Category: Killifish
Diet & Feeding
- • Diet type: Omnivore
- • Feed 1-2 times daily
- • Varied diet recommended
Tank Mate Compatibility
Compatible With
Avoid Keeping With
Care Tips
Expert Tips
Least killifish can thrive in nano tanks as small as 3-5 gallons with gentle filtration and dense planting. They prefer warm water at 68-80°F and adapt to a wide range of water chemistries. Feed micro-foods including crushed flakes, vinegar eels, micro-worms, and live or frozen baby brine shrimp. Their tiny mouths cannot handle standard-sized foods. Keep them in species-only setups or with other truly tiny, peaceful species, as virtually any common aquarium fish is large enough to eat them. They breed slowly compared to guppies, producing very small broods of 2-5 fry every few weeks. Dense vegetation provides essential cover for fry and adults. They are underappreciated gems for dedicated nano fishkeepers.
Quick Facts
19L
Min Tank (5gal)
3cm
Adult Size (1")
3yr
Lifespan
8+
Min School
Build Your Perfect Community Tank
Find compatible tankmates for your Least Killifish
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Guppy
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Tank Mates for Least Killifish
Species from our database with overlapping water parameters, compatible temperaments and a realistic shared tank size.
Blue Velvet Shrimp
Neocaridina davidi var.
easy · 5+ gal
Cherry Shrimp
Neocaridina davidi
easy · 5+ gal
Mystery Snail
Pomacea bridgesii
easy · 10+ gal
Malaysian Trumpet Snail
Melanoides tuberculata
easy · 5+ gal
Similar Care Level
Other easy-care species that suit a comparable setup.
Frequently Asked Questions
What size tank does a Least Killifish need?
A Least Killifish needs a minimum tank size of 5 gallons (19 litres). They should be kept in schools of at least 8.
What water parameters does a Least Killifish need?
Least Killifish thrive in water between 66-75°F (19-24°C) with a pH of 7.0-8.0.
Are Least Killifish easy to care for?
Least Killifish are considered easy to care for. They are peaceful fish with a lifespan of about 3 years.
How big do Least Killifish get and what do they eat?
Least Killifish reach about 1 inch and are omnivores. Least killifish can thrive in nano tanks as small as 3-5 gallons with gentle filtration and dense planting. They prefer warm water at 68-80°F and adapt to a wide range of water chemistries. Feed micro-foods including crushed flakes, vinegar eels, micro-worms, and live or frozen baby brine shrimp. Their tiny mouths cannot handle standard-sized foods. Keep them in species-only setups or with other truly tiny, peaceful species, as virtually any common aquarium fish is large enough to eat them. They breed slowly compared to guppies, producing very small broods of 2-5 fry every few weeks. Dense vegetation provides essential cover for fry and adults. They are underappreciated gems for dedicated nano fishkeepers.