Reticulated Hillstream Loach

Sewellia lineolata is widely regarded as the jewel of the hillstream hobby, its intricate reticulated pattern of cream lines on black making it one of the most visually arresting loaches available. Native to the fast-flowing rivers of central Vietnam, it uses its highly modified paired fins and flattened ventral surface to anchor itself against powerful currents and graze constantly on biofilm, diatoms, and green algae.

In the aquarium, S. lineolata rewards attentive keepers with active, engaging behaviour and, given sufficient flow and water quality, occasional spawning activity. Males are easily distinguished by the reticulated fleshy ridge on the snout and generally more intense patterning. Groups of five or more are recommended to diffuse inter-specimen territorial interactions while encouraging natural shoaling behaviour.

This species is unforgiving of stagnant or warm water. A turnover rate of 10–15× tank volume per hour, supplemented by surface agitation, is the minimum requirement. Water temperature should be kept firmly in the 18–24 °C range year-round, and nitrates must be held below 20 ppm through regular water changes.

Water: 18–24°C, pH 6.5–7.5, GH 4–15, KH 2–8; high flow (10–15× turnover/hour) and strong surface agitation are non-negotiable. Tank: Minimum 80 L, smooth river pebbles and boulders, no sharp substrate; broad flat stones essential for grazing and resting. Feeding: Primarily biofilm and algae; supplement with spirulina wafers, blanched courgette, and occasional frozen daphnia or cyclops. Breeding: Egg-scatterers spawning beneath flat stones; condition with cooler water changes and increased flow; remove eggs to a tumbler if possible. Compatibility: Peaceful with most community fish; mildly territorial with own species — keep groups of 5+ to distribute aggression.