Can Jack Dempsey and Japanese Ricefish (Medaka) Live Together?

Jack Dempsey is a semi-aggressive species (8/10), while Japanese Ricefish (Medaka) is peaceful (2/10). This notable difference means Jack Dempsey may occasionally assert dominance over Japanese Ricefish (Medaka).

Large aggression gap (6 points) between Jack Dempsey and Japanese Ricefish (Medaka) increases stress risk for the more peaceful fish.

In terms of spatial distribution, Jack Dempsey 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.

There is a critical concern: the Piscivore (Eats small/nano fish) behaviour of one fish directly conflicts with the Nano / Bite-sized (Predation Risk) trait of the other — piscivorous fish will prey on nano-sized tank mates..

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 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 8. 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. An aquarium test kit is recommended for monitoring.

To house Jack Dempsey and Japanese Ricefish (Medaka) together, plan for an aquarium of at least 240 litres with a minimum length of 120 cm. This accounts for the larger species' space requirements with an additional 20 % buffer to reduce territorial tension.

Providing a mix of open swimming space and sheltered areas with rocks, driftwood, or plants will keep both species comfortable and allow natural behaviour.

Specific environmental needs for this combination include: Sand (Sifters), Driftwood (Digestion/Hiding), Smooth Gravel (Sensitive Barbels), Plants - Densely covered, Plants - Floating. Meeting these requirements will help both species thrive.

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

Both species do well with moderate (standard) water movement, so a standard filtration setup rated for the tank volume should suffice.