Can Least Killifish (Heterandria) and Rachov's Killifish (Annual) Live Together?

Least Killifish (Heterandria) is a peaceful species (1/10), while Rachov's Killifish (Annual) is generally mild-mannered (3/10). This modest difference means Rachov's Killifish (Annual) may occasionally assert dominance over Least Killifish (Heterandria).

Least Killifish (Heterandria) and Rachov's Killifish (Annual) both frequent the Middle (Open Water) and Bottom (Substrate) region of the setup. This overlap can increase competition for space, so providing ample room and cover is important to keep both species comfortable.

Additional behavioural considerations to keep in mind: Hyperactive swimmers can stress shy, slow-moving species through constant motion.

Worth noting: Rachov's Killifish (Annual) is a known jumper, so a tight-fitting lid is essential.

To improve the chances of a peaceful coexistence in this community tank: A larger aquarium with ample hiding spots can help diffuse aggression and give the less dominant fish space to retreat.

The safe temperature window for both species falls between 20°C and 26°C. Aim for the midpoint of this range (around 23.0°C) for optimal comfort.

Both fish can tolerate a pH between 7 and 7.5. Maintaining a stable value within this band is more important than hitting an exact number.

For general hardness, the shared comfort zone is 5–12 dGH. Regular testing will ensure conditions stay within this range. An aquarium test kit is recommended for monitoring.

To house Least Killifish (Heterandria) and Rachov's Killifish (Annual) together, plan for an aquarium of at least 23 litres with a minimum length of 30 cm. This accounts for the larger species' space requirements with an additional 20 % buffer to reduce territorial tension.

Because this pairing requires extra vigilance, include plenty of hiding spots — caves, driftwood, and dense plant clusters — so the less dominant fish can retreat when needed.

Specific environmental needs for this combination include: Plants - Densely covered, Plants - Floating, Soil / Nutrient Rich, Leaf Litter/Blackwater. Meeting these requirements will help both species thrive.

Both species do well with low (still water) water movement, so a standard filtration setup rated for the tank volume should suffice.