Can Freshwater Harlequin Shrimp (Sulawesi) and Red Bellied Pacu Live Together?

Freshwater Harlequin Shrimp (Sulawesi) is a peaceful species (0/10), while Red Bellied Pacu is generally mild-mannered (4/10). This notable difference means Red Bellied Pacu may occasionally assert dominance over Freshwater Harlequin Shrimp (Sulawesi).

Freshwater Harlequin Shrimp (Sulawesi) and Red Bellied Pacu 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: Hyperactive swimmers can stress shy, slow-moving species through constant motion. Aggressive eaters may outcompete shy fish for food, leading to malnutrition.

Worth noting: Freshwater Harlequin Shrimp (Sulawesi) is nocturnal and will be most active after lights-out, naturally reducing daytime encounters. Also, Red Bellied Pacu is a known jumper, so a tight-fitting lid is essential.

To improve the chances of a peaceful coexistence in this community tank: A larger aquarium with ample hiding spots can help diffuse aggression and give the less dominant fish space to retreat.

The safe temperature window for both species falls between 26°C and 28°C. Aim for the midpoint of this range (around 27.0°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 4–8 dGH. Regular testing will ensure conditions stay within this range.

To house Freshwater Harlequin Shrimp (Sulawesi) and Red Bellied Pacu together, plan for an aquarium of at least 3800 litres with a minimum length of 300 cm. This recommendation combines the stricter species minimums with a community-load allowance so the pairing has realistic long-term space and filtration headroom.

Because this pairing requires extra vigilance, include plenty of hiding spots — caves, driftwood, and dense plant clusters — so the less dominant fish can retreat when needed.

Specific environmental needs for this combination include: Established Algae (Otocinclus), Smooth Gravel (Sensitive Barbels). 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.

This pairing usually fails when the tank is treated like a standard mixed community and the caution flags are ignored. Freshwater Harlequin Shrimp (Sulawesi) and Red Bellied Pacu need extra room, more cover, and closer observation during the first few weeks so small aggression, feeding, or territory issues do not snowball into a long-term problem.

Feeding time deserves special attention with this pairing. Red Bellied Pacu is an aggressive eater that may prevent Freshwater Harlequin Shrimp (Sulawesi) from getting enough food.

Because Red Bellied Pacu is a fast, competitive feeder, consider using sinking pellets or feeding at opposite ends of the setup to ensure Freshwater Harlequin Shrimp (Sulawesi) receives an adequate share.