Hillstream loaches, also known as butterfly loaches, are a species of freshwater fish that are native to the fast-moving streams and rivers of Southeast Asia. They have a unique flattened body shape that helps them to cling to rocks and move around in strong currents.

Hillstream loaches require specific water parameters in order to thrive in captivity. They prefer a pH range of 7.0-8.0 and a temperature range of 68-76°F (20-24°C). It's important to provide adequate water flow in the aquarium to mimic their natural habitat.

In terms of behavior, hillstream loaches are active and social fish that prefer to live in groups. They are peaceful and can be kept with other non-aggressive species, such as small tetras or rasboras.

Hillstream loaches are also known for their algae-eating abilities and can help to keep aquariums clean. They enjoy having plenty of hiding places, such as rocks and driftwood, to explore and rest on.

Overall, hillstream loaches are a fascinating and unique addition to any aquarium with the proper setup and care.