Can Marlier's Julie and Whiteseam Fighter Live Together?

Marlier's Julie is a moderately assertive species (6/10), while Whiteseam Fighter is generally mild-mannered (3/10). This modest difference means Marlier's Julie may occasionally assert dominance over Whiteseam Fighter.

Marlier's Julie and Whiteseam Fighter both frequent the Bottom (Substrate) 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.

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 Marlier's Julie (8.2–9.3) and Whiteseam Fighter (4–6.5) do not overlap, making it impossible to satisfy both species simultaneously.

Hardness requirements are incompatible: Marlier's Julie needs 10–25 dGH while Whiteseam Fighter requires 1–5 dGH.

To house Marlier's Julie and Whiteseam Fighter together, plan for an aquarium of at least 114 litres with a minimum length of 80 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: Sand (Sifters), Leaf Litter/Blackwater, Plants - Densely covered, Plants - Floating. Meeting these requirements will help both species thrive.

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

Marlier's Julie 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.