Can Flowerhorn Cichlid and Least Killifish (Heterandria) Live Together?

Flowerhorn Cichlid is a highly aggressive species (10/10), while Least Killifish (Heterandria) is peaceful (1/10). This notable difference means Flowerhorn Cichlid may occasionally assert dominance over Least Killifish (Heterandria).

Large aggression gap (9 points) between Flowerhorn Cichlid and Least Killifish (Heterandria) increases stress risk for the more peaceful fish.

Flowerhorn Cichlid and Least Killifish (Heterandria) 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.

There is a critical concern: the Piscivore (Eats small/nano fish) behaviour of one fish directly conflicts with the Nano / Bite-sized (Predation Risk) trait of the other — piscivorous fish will prey on nano-sized tank mates..

Additional behavioural considerations to keep in mind: Aggressive fish may bully and stress shy, slow-moving species.

The safe temperature window for both species falls between 26°C and 27°C. Aim for the midpoint of this range (around 26.5°C) for optimal comfort.

Both fish can tolerate a pH between 7.4 and 8. Maintaining a stable value within this band is more important than hitting an exact number.

For general hardness, the shared comfort zone is 9–20 dGH. Regular testing will ensure conditions stay within this range. An aquarium test kit is recommended for monitoring.

To house Flowerhorn Cichlid and Least Killifish (Heterandria) together, plan for an aquarium of at least 336 litres with a minimum length of 120 cm. This accounts for the larger species' space requirements with an additional 20 % buffer to reduce territorial tension.

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: Sand (Sifters), Smooth Gravel (Sensitive Barbels), Plants - Densely covered, Plants - Floating. Meeting these requirements will help both species thrive.

Note a potential conflict in setup requirements: Flowerhorn Cichlid is a plant destroyer, which conflicts with Least Killifish (Heterandria)'s requirement for live plants. Compromise where possible or prioritise the more critical need.

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