Can Least Killifish (Heterandria) and Whiteseam Fighter Live Together?

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

Least Killifish (Heterandria) and Whiteseam Fighter 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: Shrimp eaters may also prey on very small nano fish.

Worth noting: Whiteseam Fighter is a known jumper, so a tight-fitting lid is essential.

The safe temperature window for both species falls between 23°C and 27°C. Aim for the midpoint of this range (around 25.0°C) for optimal comfort.

The pH requirements of Least Killifish (Heterandria) (7–8) and Whiteseam Fighter (4–6.5) do not overlap, making it impossible to satisfy both species simultaneously.

For general hardness, the shared comfort zone is 5–5 dGH. Regular testing will ensure conditions stay within this range.

To house Least Killifish (Heterandria) and Whiteseam Fighter together, plan for an aquarium of at least 38 litres with a minimum length of 45 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 Whiteseam Fighter are the kind of pair that can look acceptable in a shop but become a maintenance problem at home. The main risk is not a single number in the chart; it is the way incompatible behavior, water needs, or pressure on space compounds over time once both fish are established in the same tank.

Feeding time deserves special attention with this pairing. Whiteseam Fighter is a known shrimp eater and may prey on small invertebrates or nano fish like Least Killifish (Heterandria).