Least Killifish (Heterandria formosa)

The Least Killifish (Heterandria formosa) is a fascinating aquatic creature. Let’s dive into some intriguing details about this diminutive fish:

1. Size and Uniqueness:

   • The least killifish is one of the smallest fish species in the world.
   • Males reach a mere 1.2 inches in length, while females can grow up to 1.5 inches
   • Despite their small size, they are hardy, adaptable, and surprisingly social.

2. Natural Habitat:

   • These tiny fish are predominantly found in freshwater environments, but they can also survive in brackish conditions.
   • In the wild, least killifish inhabit sluggish waterways, stagnant ponds, and areas with marginal plants or heavy vegetation.
   • Their natural range includes the coastal lowlands of Alabama and South Pine Hills¹.

3. Tank Requirements:

   • Due to their diminutive size, least killifish can thrive in small aquaria.
   • A 5-gallon aquarium is sufficient if you’re keeping them alone.
   • For a larger colony or tank mates, consider a 10-gallon tank.
   • These fish aren’t great jumpers, so you can even keep them without a lid.
   • Decorate the tank with lots of plants (avoid spider wood) and provide hiding spots using materials like dragon stones.
   • Use sand or river stones as substrate, and consider stabilizing the pH level with limestones, crushed coral, or Texas holey rock¹.

4. Diet and Adaptability:

   • Least killifish are omnivorous and can adapt to various water conditions.
   • They’ll happily feed on live or frozen foods, including small insects, daphnia, and flake foods.
   • Their hardiness makes them ideal for beginner breeders and those with smaller tanks