Can Least Killifish (Heterandria) and Marbled Hatchetfish Live Together?

Both Least Killifish (Heterandria) and Marbled Hatchetfish are peaceful species with an aggression score of 1/10. Their matching temperaments mean neither fish is likely to dominate the other in a shared aquarium.

Least Killifish (Heterandria) and Marbled Hatchetfish both frequent the Top (Surface) region of the setup. This overlap can increase competition for space, so providing ample room and cover is important to keep both species comfortable.

Worth noting: Marbled Hatchetfish is a known jumper, so a tight-fitting lid is essential.

The safe temperature window for both species falls between 24°C and 27°C. Aim for the midpoint of this range (around 25.5°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.

To house Least Killifish (Heterandria) and Marbled Hatchetfish together, plan for an aquarium of at least 60 litres with a minimum length of 60 cm. This recommendation combines the stricter species minimums with a community-load allowance so the pairing has realistic long-term space and filtration headroom.

Providing a mix of open swimming space and sheltered areas with rocks, driftwood, or plants will keep both species comfortable and allow natural behaviour.

Specific environmental needs for this combination include: Plants - Densely covered, Plants - Floating, 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.

Least Killifish (Heterandria) and Marbled Hatchetfish work best when the tank gives each fish enough room to use its preferred level of the aquarium and enough cover to avoid constant visual contact. The score matters, but the real-world success usually comes from matching their pace, keeping water stable, and resisting the urge to crowd the tank just because the pair looks safe on paper.