Can Least Killifish (Heterandria) and Royal Pleco (L190) Live Together?

Least Killifish (Heterandria) is a peaceful species (1/10), while Royal Pleco (L190) is moderately assertive (5/10). This notable difference means Royal Pleco (L190) may occasionally assert dominance over Least Killifish (Heterandria).

Least Killifish (Heterandria) and Royal Pleco (L190) 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: Royal Pleco (L190) is nocturnal and will be most active after lights-out, naturally reducing daytime encounters.

To improve the chances of a peaceful coexistence in this community tank: Provide a significantly larger tank (at least 50% more volume than the minimum) to allow both Least Killifish (Heterandria) and Royal Pleco (L190) to establish separate territories. Add plenty of line-of-sight breaks using driftwood, rocks, and dense planting to reduce territorial confrontations. 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 22°C and 27°C. Aim for the midpoint of this range (around 24.5°C) for optimal comfort.

Both fish can tolerate a pH between 7 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 5–15 dGH. Regular testing will ensure conditions stay within this range. An aquarium test kit is recommended for monitoring.

To house Least Killifish (Heterandria) and Royal Pleco (L190) together, plan for an aquarium of at least 540 litres with a minimum length of 150 cm. This accounts for the larger species' space requirements with an additional 20 % buffer to reduce territorial tension.

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: Plants - Densely covered, Plants - Floating, Driftwood (Digestion/Hiding). Meeting these requirements will help both species thrive.

Note a potential conflict in setup requirements: Royal Pleco (L190) is a plant destroyer, which conflicts with Least Killifish (Heterandria)'s requirement for live plants. Compromise where possible or prioritise the more critical need.

Least Killifish (Heterandria) prefers Low (Still Water) flow while Royal Pleco (L190) needs High (River/Stream) flow. Consider positioning filter outlets and using baffles to create zones of different current intensity within the same tank.