What size tank does a Least Killifish need?

Least Killifish needs a minimum of 5 gallons, with 8 gallons recommended. They are middle swimmers. Keep in groups of 4+.

Is Least Killifish good for beginners?

Least Killifish is rated "intermediate" difficulty (2/5). Great for beginners.

What fish are compatible with Least Killifish?

Least Killifish is peaceful. Compatible tank mates include other peaceful fish with similar water parameters (pH 7-8, temp 68-78°F).

Least Killifish

Heterandria formosa

Family: Poeciliidae • Origin: Various

Least Killifish (Heterandria formosa) is a peaceful livebearer reaching 1.2 inches. Keep in groups of 4+. Minimum tank size: 5 gallons.

Min Tank

5 gal

Max Size

1.2"

Temperature

68-78°F

7-8

Lifespan

2 years

School Size

Swim Level

middle

Hardness

5-15 dGH

peacefulintermediateomnivoreschooling

Is Least Killifish Right for Your Tank?

Least Killifish is an excellent choice for beginners — rated "intermediate" difficulty (2/5). They're hardy, forgiving of minor water parameter fluctuations, and generally easy to feed. At just 5 gallons minimum, they work well in nano tanks and smaller setups.

With a peaceful temperament, Least Killifish makes a great community fish. They coexist well with other non-aggressive species of similar size. This is a schooling species — keep at least 4 together, or they may become stressed and display abnormal behavior. Expected lifespan: 2 years with proper care.

Common Mistakes with Least Killifish

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Keeping fewer than 4 together

Least Killifish is a schooling species — they need a group of at least 4 to feel secure. Lone or paired individuals become stressed, hide constantly, and may develop health issues or aggression.

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Putting them in a tank under 5 gallons

While 5 gallons is the minimum, nano tanks require more frequent water changes and leave less room for error. A slightly larger tank (8 gal) is much more forgiving.