Can Least Killifish (Heterandria) and Three Spot Gourami (Blue/Gold/Opaline) Live Together?

Least Killifish (Heterandria) is a peaceful species (1/10), while Three Spot Gourami (Blue/Gold/Opaline) is moderately assertive (6/10). This notable difference means Three Spot Gourami (Blue/Gold/Opaline) may occasionally assert dominance over Least Killifish (Heterandria).

Least Killifish (Heterandria) and Three Spot Gourami (Blue/Gold/Opaline) both frequent the Top (Surface) and Middle (Open Water) 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.

To improve the chances of a peaceful coexistence in this community tank: Provide a significantly larger tank (at least 50% more volume than the minimum) to allow both Least Killifish (Heterandria) and Three Spot Gourami (Blue/Gold/Opaline) to establish separate territories. Add plenty of line-of-sight breaks using driftwood, rocks, and dense planting to reduce territorial confrontations. A larger aquarium with ample hiding spots can help diffuse aggression and give the less dominant fish space to retreat. Keep fin nippers in larger groups to distribute nipping behaviour among conspecifics rather than tank mates.

The safe temperature window for both species falls between 22°C and 27°C. Aim for the midpoint of this range (around 24.5°C) for optimal comfort.

Both fish can tolerate a pH between 7 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 5–20 dGH. Regular testing will ensure conditions stay within this range. An aquarium test kit is recommended for monitoring.

To house Least Killifish (Heterandria) and Three Spot Gourami (Blue/Gold/Opaline) together, plan for an aquarium of at least 132 litres with a minimum length of 90 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. 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.