Can Northern Mountain Swordtail and Thai Micro Crab Live Together?

Northern Mountain Swordtail is a generally mild-mannered species (3/10), while Thai Micro Crab is peaceful (0/10). This modest difference means Northern Mountain Swordtail may occasionally assert dominance over Thai Micro Crab.

In terms of spatial distribution, Northern Mountain Swordtail 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.

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, Northern Mountain Swordtail 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 22°C and 25°C. Aim for the midpoint of this range (around 23.5°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 Northern Mountain Swordtail and Thai Micro Crab together, plan for an aquarium of at least 110 litres with a minimum length of 90 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, Plants - Floating, Leaf Litter/Blackwater. Meeting these requirements will help both species thrive.

Northern Mountain Swordtail prefers High (River/Stream) flow while Thai Micro Crab needs Low (Still Water) flow. Consider positioning filter outlets and using baffles to create zones of different current intensity within the same tank.

This pairing usually fails when the tank is treated like a standard mixed community and the caution flags are ignored. Northern Mountain Swordtail and Thai Micro Crab need extra room, more cover, and closer observation during the first few weeks so small aggression, feeding, or territory issues do not snowball into a long-term problem.