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

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

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

Japanese Ricefish (Medaka) and Largemouth Bass 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.

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..

Additional behavioural considerations to keep in mind: Shrimp eaters may also prey on very small nano fish.

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 10°C and 28°C. Aim for the midpoint of this range (around 19.0°C) for optimal comfort.

Both fish can tolerate a pH between 6.5 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 5–25 dGH. Regular testing will ensure conditions stay within this range.

To house Japanese Ricefish (Medaka) and Largemouth Bass together, plan for an aquarium of at least 1135 litres with a minimum length of 240 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, Driftwood (Digestion/Hiding). Meeting these requirements will help both species thrive.

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

Japanese Ricefish (Medaka) and Largemouth 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.

Feeding time deserves special attention with this pairing. Largemouth Bass is a known shrimp eater and may prey on small invertebrates or nano fish like Japanese Ricefish (Medaka).

Because Largemouth Bass is a fast, competitive feeder, consider using sinking pellets or feeding at opposite ends of the setup to ensure Japanese Ricefish (Medaka) receives an adequate share.