Can Least Killifish (Heterandria) and Mono Sebae (Brackish) Live Together?

Least Killifish (Heterandria) is a peaceful species (1/10), while Mono Sebae (Brackish) is generally mild-mannered (4/10). This modest difference means Mono Sebae (Brackish) may occasionally assert dominance over Least Killifish (Heterandria).

Least Killifish (Heterandria) and Mono Sebae (Brackish) both frequent the 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. Aggressive eaters may outcompete shy fish for food, leading to malnutrition. Shrimp eaters may also prey on very small nano fish.

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 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 7.5 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 12–20 dGH. Regular testing will ensure conditions stay within this range. An aquarium test kit is recommended for monitoring.

To house Least Killifish (Heterandria) and Mono Sebae (Brackish) together, plan for an aquarium of at least 480 litres with a minimum length of 150 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, Sand (Sifters), Smooth Gravel (Sensitive Barbels). Meeting these requirements will help both species thrive.

Note a potential conflict in setup requirements: Mono Sebae (Brackish) 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 low (still water) water movement, so a standard filtration setup rated for the tank volume should suffice.

Feeding time deserves special attention with this pairing. Mono Sebae (Brackish) is a known shrimp eater and may prey on small invertebrates or nano fish like Least Killifish (Heterandria). Mono Sebae (Brackish) is an aggressive eater that may prevent Least Killifish (Heterandria) from getting enough food.

Because Mono Sebae (Brackish) is a fast, competitive feeder, consider using sinking pellets or feeding at opposite ends of the setup to ensure Least Killifish (Heterandria) receives an adequate share.