Can Dwarf Molly and Red Swamp Crayfish Live Together?

Dwarf Molly is a generally mild-mannered species (3/10), while Red Swamp Crayfish is highly aggressive (9/10). This notable difference means Red Swamp Crayfish may occasionally assert dominance over Dwarf Molly.

Large aggression gap (6 points) between Dwarf Molly and Red Swamp Crayfish increases stress risk for the more peaceful fish.

In terms of spatial distribution, Dwarf Molly prefers the Top (Surface) and Middle (Open Water) zones, whereas Red Swamp Crayfish 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.

Worth noting: Red Swamp Crayfish is a known jumper, so a tight-fitting lid is essential.

To improve the chances of a peaceful coexistence in this community tank: Provide a significantly larger tank (at least 50% more volume than the minimum) to allow both Dwarf Molly and Red Swamp Crayfish to establish separate territories. Add plenty of line-of-sight breaks using driftwood, rocks, and dense planting to reduce territorial confrontations. 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 22°C and 28°C. Aim for the midpoint of this range (around 25.0°C) for optimal comfort.

Both fish can tolerate a pH between 6.5 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 10–20 dGH. Regular testing will ensure conditions stay within this range.

To house Dwarf Molly and Red Swamp Crayfish together, plan for an aquarium of at least 75 litres with a minimum length of 60 cm. This recommendation combines the stricter species minimums with a community-load allowance so the pairing has realistic long-term space and filtration headroom.

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, Established Algae (Otocinclus), Driftwood (Digestion/Hiding), Leaf Litter/Blackwater, Shells (Breeding/Hiding). Meeting these requirements will help both species thrive.

Note a potential conflict in setup requirements: Red Swamp Crayfish is a plant destroyer, which conflicts with Dwarf Molly's requirement for live plants. Compromise where possible or prioritise the more critical need.

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