Can Arapaima and Kuhli Loach Live Together?

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

Large aggression gap (7 points) between Arapaima and Kuhli Loach increases stress risk for the more peaceful fish.

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

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

Worth noting: Kuhli Loach 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.

To improve the chances of a peaceful coexistence in this community tank: 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 24°C and 30°C. Aim for the midpoint of this range (around 27.0°C) for optimal comfort.

Both fish can tolerate a pH between 6 and 7. Maintaining a stable value within this band is more important than hitting an exact number.

For general hardness, the shared comfort zone is 3–10 dGH. Regular testing will ensure conditions stay within this range.

To house Arapaima and Kuhli Loach 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.

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: Sand (Sifters), Leaf Litter/Blackwater, Smooth Gravel (Sensitive Barbels), Plants - Densely covered. Meeting these requirements will help both species thrive.

Note a potential conflict in setup requirements: Arapaima is a plant destroyer, which conflicts with Kuhli Loach'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.