Can Freshwater Harlequin Shrimp (Sulawesi) and Regan's Julie Live Together?

Freshwater Harlequin Shrimp (Sulawesi) is a peaceful species (0/10), while Regan's Julie is semi-aggressive (7/10). This notable difference means Regan's Julie may occasionally assert dominance over Freshwater Harlequin Shrimp (Sulawesi).

Large aggression gap (7 points) between Freshwater Harlequin Shrimp (Sulawesi) and Regan's Julie increases stress risk for the more peaceful fish.

Freshwater Harlequin Shrimp (Sulawesi) and Regan's Julie 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: Freshwater Harlequin Shrimp (Sulawesi) 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 27°C. Aim for the midpoint of this range (around 26.5°C) for optimal comfort.

Both fish can tolerate a pH between 8 and 8.5. Maintaining a stable value within this band is more important than hitting an exact number.

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

To house Freshwater Harlequin Shrimp (Sulawesi) and Regan's Julie 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: Established Algae (Otocinclus), Smooth Gravel (Sensitive Barbels), Sand (Sifters). 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.

Freshwater Harlequin Shrimp (Sulawesi) and Regan's Julie 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.