Can Flagtail Prochilodus and Japanese Ricefish (Medaka) Live Together?

Flagtail Prochilodus is a moderately assertive species (6/10), while Japanese Ricefish (Medaka) is peaceful (2/10). This notable difference means Flagtail Prochilodus may occasionally assert dominance over Japanese Ricefish (Medaka).

In terms of spatial distribution, Flagtail Prochilodus prefers the Middle (Open Water) and Bottom (Substrate) zones, whereas Japanese Ricefish (Medaka) occupies the Top (Surface) zone. Because they use different levels of the water column, territorial disputes are less likely and the tank will appear more balanced.

Worth noting: Flagtail Prochilodus 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 23°C and 28°C. Aim for the midpoint of this range (around 25.5°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 Flagtail Prochilodus and Japanese Ricefish (Medaka) together, plan for an aquarium of at least 500 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: Established Algae (Otocinclus), Driftwood (Digestion/Hiding), Plants - Densely covered, Plants - Floating. Meeting these requirements will help both species thrive.

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

Flagtail Prochilodus prefers High (River/Stream) flow while Japanese Ricefish (Medaka) 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. Flagtail Prochilodus and Japanese Ricefish (Medaka) 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.