Can Dusky Millions Fish and Mexican Dwarf Crayfish (CPO) Live Together?

Dusky Millions Fish is a peaceful species (2/10), while Mexican Dwarf Crayfish (CPO) is generally mild-mannered (4/10). This modest difference means Mexican Dwarf Crayfish (CPO) may occasionally assert dominance over Dusky Millions Fish.

In terms of spatial distribution, Dusky Millions Fish prefers the Top (Surface) and Middle (Open Water) zones, whereas Mexican Dwarf Crayfish (CPO) occupies the Bottom (Substrate) zone. Because they use different levels of the water column, territorial disputes are less likely and the tank will appear more balanced.

The safe temperature window for both species falls between 16°C and 24°C. Aim for the midpoint of this range (around 20.0°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 8–15 dGH. Regular testing will ensure conditions stay within this range.

To house Dusky Millions Fish and Mexican Dwarf Crayfish (CPO) together, plan for an aquarium of at least 40 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, Established Algae (Otocinclus), Sand (Sifters), Driftwood (Digestion/Hiding), 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.

Dusky Millions Fish and Mexican Dwarf Crayfish (CPO) work best when the tank gives each fish enough room to use its preferred level of the aquarium and enough cover to avoid constant visual contact. The score matters, but the real-world success usually comes from matching their pace, keeping water stable, and resisting the urge to crowd the tank just because the pair looks safe on paper.