Can Japanese Ricefish (Medaka) and Royal Pleco (L190) Live Together?

Japanese Ricefish (Medaka) is a peaceful species (2/10), while Royal Pleco (L190) is moderately assertive (5/10). This modest difference means Royal Pleco (L190) may occasionally assert dominance over Japanese Ricefish (Medaka).

In terms of spatial distribution, Japanese Ricefish (Medaka) prefers the Top (Surface) zone, whereas Royal Pleco (L190) 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: Royal Pleco (L190) is nocturnal and will be most active after lights-out, naturally reducing daytime encounters. Also, Japanese Ricefish (Medaka) 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 Japanese Ricefish (Medaka) and Royal Pleco (L190) to establish separate territories. Add plenty of line-of-sight breaks using driftwood, rocks, and dense planting to reduce territorial confrontations.

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 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 5–15 dGH. Regular testing will ensure conditions stay within this range.

To house Japanese Ricefish (Medaka) and Royal Pleco (L190) together, plan for an aquarium of at least 450 litres with a minimum length of 150 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.

Note a potential conflict in setup requirements: Royal Pleco (L190) is a plant destroyer, which conflicts with Japanese Ricefish (Medaka)'s requirement for live plants. Compromise where possible or prioritise the more critical need.

Japanese Ricefish (Medaka) prefers Low (Still Water) flow while Royal Pleco (L190) 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 Royal Pleco (L190) 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.