Chameleon Loach

Erromyzon sinensis is one of the most unusual hillstream loaches available to the specialist keeper, possessing the remarkable ability to change colour rapidly in response to its background substrate — earning it the common name Chameleon Loach. The colour-change mechanism involves rapid redistribution of chromatophores and is most dramatic when fish move between dark and pale substrates. In repose on a pale stone, the species displays a subtle warm grey patterning; moved to a dark substrate, it rapidly darkens to near-black.

Native to the river systems of southern China, E. sinensis inhabits the same type of fast-flowing, cool, highly oxygenated hill streams as Beaufortia and Pseudogastromyzon species, and its care requirements follow the same demanding template. Water temperature must be maintained in the 18–24 °C range, strong flow and near-saturated dissolved oxygen are non-negotiable, and organic waste must be minimised through regular water changes and excellent mechanical filtration.

The Chameleon Loach is an advanced-level species not because it is particularly fragile, but because it demands consistently excellent water conditions and cool temperatures year-round. Keepers in warm climates must invest in a chiller. In a well-maintained specialist hillstream aquarium, however, E. sinensis is a highly rewarding and genuinely unique fish whose colour-change ability alone makes it a remarkable display species.

Water: 18–24°C, pH 6.5–7.5, GH 4–15, KH 2–8; high flow and near-saturated dissolved oxygen essential; a chiller is recommended in warm climates. Tank: 80 L minimum; mix of pale and dark-coloured smooth stones to demonstrate the colour-change behaviour; strong directional flow throughout. Feeding: Herbivore — biofilm, diatoms, and green algae; supplement with spirulina wafers, Repashy algae gel food, and blanched greens. Breeding: Not documented in captivity; condition with cool water changes and increased flow; treat as per other Chinese hillstream loaches. Compatibility: Peaceful; suitable for mixed Chinese hillstream biotopes; its colour-change ability is best appreciated in a well-lit tank with contrasting substrate areas.