Can Japanese Ricefish (Medaka) and Mountain Rainbowfish Live Together?

Both Japanese Ricefish (Medaka) and Mountain Rainbowfish are peaceful species with an aggression score of 2/10. Their matching temperaments mean neither fish is likely to dominate the other in a shared aquarium.

Japanese Ricefish (Medaka) and Mountain Rainbowfish both frequent the Top (Surface) region of the setup. This overlap can increase competition for space, so providing ample room and cover is important to keep both species comfortable.

Worth noting: Japanese Ricefish (Medaka) is a known jumper, so a tight-fitting lid is essential.

The safe temperature window for both species falls between 17°C and 24°C. Aim for the midpoint of this range (around 20.5°C) for optimal comfort.

Both fish can tolerate a pH between 7.4 and 8.5. Maintaining a stable value within this band is more important than hitting an exact number.

For general hardness, the shared comfort zone is 8–20 dGH. Regular testing will ensure conditions stay within this range.

To house Japanese Ricefish (Medaka) and Mountain Rainbowfish 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, Driftwood (Digestion/Hiding). Meeting these requirements will help both species thrive.

Japanese Ricefish (Medaka) prefers Low (Still Water) flow while Mountain Rainbowfish needs High (River/Stream) 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. Japanese Ricefish (Medaka) and Mountain Rainbowfish 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.