Least Killifish

Heterandria formosa

Least Killifish (Heterandria formosa) — Easy care, Semi-aggressive, under Livebearer & Killifish. Minimum tank in the app: 5.3 US gal min; aim for 68–79°F and pH 6.8–8.2. The Least Killifish is ideal for small, well-planted tanks and offers a unique charm with its vibrant colors and small stature.

Least Killifish (Heterandria formosa) in a planted freshwater aquarium
Care levelEasy
TemperamentSemi-aggressive
Min tank size5.3 US gal min
pH range6.8–8.2
Temperature68–79°F
Max size1.4 in (3.5 cm)
Captive lifespan2–4 years
SchoolingYes · 6+ recommended

Captive lifespan reflects typical experience in a home aquarium, not maximum recorded age; genetics, sourcing, and care vary.

Natural distribution

Americas / Africa (varies)

  • Africa
  • South America
  • Central America & Mexico

Regional colours match the stocking calculator’s origin map.

Least Killifish Tank Setup

Aim for a densely planted tank with plenty of hiding spots and open swimming space in the top and mid-levels. A gentle flow and subdued lighting can enhance their natural behavior, while a fine substrate helps mimic their natural habitat and reduces stress during foraging.

What Do Least Killifishs Eat?

Feeding can be competitive, so provide diverse food options to ensure all fish receive adequate nutrition. Their omnivorous diet means they appreciate both plant and protein sources, which can enhance their coloration and overall health.

Least Killifish Tank Mates

Best suited with similarly-sized, peaceful species that occupy different swimming zones, such as small tetras or rasboras. Avoid larger or more aggressive fish that may intimidate them, and ensure a minimum group size of six to mitigate aggression among themselves.

Are Least Killifishs Good for Beginners?

In App-aquatic we file this under easy care. That still means a cycled tank, realistic stocking, and parameters that do not swing every weekend. Aquarists often underestimate their need for social structure by keeping them in small numbers, leading to stress and aggression. neglecting water quality within their preferred pH and temperature range can result in health issues.

Building a community? Run the full list through the stocking calculator before you add anything else.

Log tests and reminders in App-aquatic—free, same data you see here.