Can Arapaima and Thai Micro Crab Live Together?

Arapaima is a semi-aggressive species (7/10), while Thai Micro Crab is peaceful (0/10). This notable difference means Arapaima may occasionally assert dominance over Thai Micro Crab.

Large aggression gap (7 points) between Arapaima and Thai Micro Crab increases stress risk for the more peaceful fish.

In terms of spatial distribution, Arapaima prefers the Top (Surface) and Middle (Open Water) zones, whereas Thai Micro Crab 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.

There is a critical concern: the Piscivore (Eats small/nano fish) behaviour of one fish directly conflicts with the Nano / Bite-sized (Predation Risk) trait of the other — piscivorous fish will prey on nano-sized tank mates..

Additional behavioural considerations to keep in mind: Hyperactive swimmers can stress shy, slow-moving species through constant motion.

Worth noting: Thai Micro Crab is nocturnal and will be most active after lights-out, naturally reducing daytime encounters. Also, Arapaima is a known jumper, so a tight-fitting lid is essential.

The safe temperature window for both species falls between 24°C and 28°C. Aim for the midpoint of this range (around 26.0°C) for optimal comfort.

Both fish can tolerate a pH between 6.5 and 7.5. Maintaining a stable value within this band is more important than hitting an exact number.

For general hardness, the shared comfort zone is 6–15 dGH. Regular testing will ensure conditions stay within this range.

To house Arapaima and Thai Micro Crab together, plan for an aquarium of at least 15000 litres with a minimum length of 600 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.

Note a potential conflict in setup requirements: Arapaima is a plant destroyer, which conflicts with Thai Micro Crab's requirement for live plants. Compromise where possible or prioritise the more critical need.

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