Can Fiddler Crab (Brackish) and Flagtail Prochilodus Live Together?

Fiddler Crab (Brackish) is a generally mild-mannered species (3/10), while Flagtail Prochilodus is moderately assertive (6/10). This modest difference means Flagtail Prochilodus may occasionally assert dominance over Fiddler Crab (Brackish).

Fiddler Crab (Brackish) and Flagtail Prochilodus 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.

Worth noting: Flagtail Prochilodus is a known jumper, so a tight-fitting lid is essential.

The safe temperature window for both species falls between 24°C and 28°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 7.5. Maintaining a stable value within this band is more important than hitting an exact number.

For general hardness, the shared comfort zone is 10–15 dGH. Regular testing will ensure conditions stay within this range.

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 Fiddler Crab (Brackish) and Flagtail Prochilodus together, plan for an aquarium of at least 500 litres with a minimum length of 150 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), Driftwood (Digestion/Hiding), Established Algae (Otocinclus). Meeting these requirements will help both species thrive.

Fiddler Crab (Brackish) prefers Low (Still Water) flow while Flagtail Prochilodus needs High (River/Stream) flow. Consider positioning filter outlets and using baffles to create zones of different current intensity within the same tank.

Fiddler Crab (Brackish) and Flagtail Prochilodus 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.