Can Freshwater Flounder and Freshwater Harlequin Shrimp (Sulawesi) Live Together?

Freshwater Flounder is a peaceful species (2/10), while Freshwater Harlequin Shrimp (Sulawesi) is peaceful (0/10). This modest difference means Freshwater Flounder may occasionally assert dominance over Freshwater Harlequin Shrimp (Sulawesi).

Freshwater Flounder and Freshwater Harlequin Shrimp (Sulawesi) both frequent the Bottom (Substrate) region of the setup. This overlap can increase competition for space, so providing ample room and cover is important to keep both species comfortable.

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

Worth noting: Freshwater Flounder is nocturnal and will be most active after lights-out, naturally reducing daytime encounters.

The safe temperature window for both species falls between 26°C and 26°C. Aim for the midpoint of this range (around 26.0°C) for optimal comfort.

Both fish can tolerate a pH between 7.5 and 8.5. Maintaining a stable value within this band is more important than hitting an exact number.

Hardness requirements are incompatible: Freshwater Flounder needs 10–25 dGH while Freshwater Harlequin Shrimp (Sulawesi) requires 4–8 dGH.

Crucially, these species require different water types — one needs freshwater while the other requires brackish conditions. This is a hard barrier to keeping them together.

To house Freshwater Flounder and Freshwater Harlequin Shrimp (Sulawesi) together, plan for an aquarium of at least 110 litres with a minimum length of 90 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: Sand (Sifters), Established Algae (Otocinclus), Smooth Gravel (Sensitive Barbels). Meeting these requirements will help both species thrive.

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

Freshwater Flounder and Freshwater Harlequin Shrimp (Sulawesi) 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. Freshwater Flounder is a known shrimp eater and may prey on small invertebrates or nano fish like Freshwater Harlequin Shrimp (Sulawesi).