Can Japanese Ricefish (Medaka) and Smallmouth Bass Live Together?

Japanese Ricefish (Medaka) is a peaceful species (2/10), while Smallmouth Bass is semi-aggressive (7/10). This notable difference means Smallmouth Bass may occasionally assert dominance over Japanese Ricefish (Medaka).

In terms of spatial distribution, Japanese Ricefish (Medaka) prefers the Top (Surface) zone, whereas Smallmouth Bass occupies the Middle (Open Water) and Bottom (Substrate) zones. 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 Nano / Bite-sized (Predation Risk) behaviour of one fish directly conflicts with the Piscivore (Eats small/nano fish) 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 15°C and 25°C. Aim for the midpoint of this range (around 20.0°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 5–20 dGH. Regular testing will ensure conditions stay within this range.

To house Japanese Ricefish (Medaka) and Smallmouth Bass together, plan for an aquarium of at least 680 litres with a minimum length of 180 cm. This recommendation combines the stricter species minimums with a community-load allowance so the pairing has realistic long-term space and filtration headroom.

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: Plants - Densely covered, Plants - Floating, Smooth Gravel (Sensitive Barbels), Driftwood (Digestion/Hiding). Meeting these requirements will help both species thrive.

Japanese Ricefish (Medaka) prefers Low (Still Water) flow while Smallmouth Bass needs High (River/Stream) flow. Consider positioning filter outlets and using baffles to create zones of different current intensity within the same tank.

Japanese Ricefish (Medaka) and Smallmouth Bass are the kind of pair that can look acceptable in a shop but become a maintenance problem at home. The main risk is not a single number in the chart; it is the way incompatible behavior, water needs, or pressure on space compounds over time once both fish are established in the same tank.