Can Betta Macrostoma and Japanese Ricefish (Medaka) Live Together?

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

Betta Macrostoma and Japanese Ricefish (Medaka) 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 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..

Additional behavioural considerations to keep in mind: Hyperactive swimmers can stress shy, slow-moving species through constant motion. Shrimp eaters may also prey on very small nano fish.

Worth noting: Betta Macrostoma is a known jumper, so a tight-fitting lid is essential.

The safe temperature window for both species falls between 20°C and 25°C. Aim for the midpoint of this range (around 22.5°C) for optimal comfort.

The pH requirements of Betta Macrostoma (4–6) and Japanese Ricefish (Medaka) (6.5–8.5) do not overlap, making it impossible to satisfy both species simultaneously.

For general hardness, the shared comfort zone is 5–5 dGH. Regular testing will ensure conditions stay within this range.

To house Betta Macrostoma and Japanese Ricefish (Medaka) together, plan for an aquarium of at least 80 litres with a minimum length of 60 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: Leaf Litter/Blackwater, Driftwood (Digestion/Hiding), Plants - Floating, Plants - Densely covered. 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.

Betta Macrostoma and Japanese Ricefish (Medaka) 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. Betta Macrostoma is a known shrimp eater and may prey on small invertebrates or nano fish like Japanese Ricefish (Medaka).