Can Betta Macrostoma and Threadfin Rainbowfish Live Together?

Betta Macrostoma is a moderately assertive species (6/10), while Threadfin Rainbowfish is peaceful (1/10). This notable difference means Betta Macrostoma may occasionally assert dominance over Threadfin Rainbowfish.

Betta Macrostoma and Threadfin Rainbowfish both frequent the Top (Surface) and Middle (Open Water) 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. Aggressive eaters may outcompete shy fish for food, leading to malnutrition. 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 23°C and 25°C. Aim for the midpoint of this range (around 24.0°C) for optimal comfort.

Both fish can tolerate a pH between 5.5 and 6. Maintaining a stable value within this band is more important than hitting an exact number.

For general hardness, the shared comfort zone is 1–5 dGH. Regular testing will ensure conditions stay within this range.

To house Betta Macrostoma and Threadfin Rainbowfish 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 Threadfin Rainbowfish 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 Threadfin Rainbowfish. Threadfin Rainbowfish is an aggressive eater that may prevent Betta Macrostoma from getting enough food.

Because Threadfin Rainbowfish is a fast, competitive feeder, consider using sinking pellets or feeding at opposite ends of the setup to ensure Betta Macrostoma receives an adequate share.