Can Golden Wonder Killifish and Marlier's Julie Live Together?

Both Golden Wonder Killifish and Marlier's Julie are moderately assertive species with an aggression score of 6/10. Their matching temperaments mean neither fish is likely to dominate the other in a shared aquarium.

In terms of spatial distribution, Golden Wonder Killifish prefers the Top (Surface) zone, whereas Marlier's Julie occupies the Bottom (Substrate) and Middle (Open Water) zones. Because they use different levels of the water column, territorial disputes are less likely and the tank will appear more balanced.

Worth noting: Golden Wonder Killifish 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 Golden Wonder Killifish (6–7.5) and Marlier's Julie (8.2–9.3) do not overlap, making it impossible to satisfy both species simultaneously.

For general hardness, the shared comfort zone is 10–20 dGH. Regular testing will ensure conditions stay within this range.

To house Golden Wonder Killifish and Marlier's Julie 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: Plants - Floating, Sand (Sifters). 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.

Golden Wonder Killifish and Marlier's Julie 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.