Reticulated hillstream loach

The reticulated hillstream loach (Sewellia lineolata) is a specialised freshwater fish from the swift, oxygen-rich streams of central Vietnam. Its flattened body and large, horizontally aligned pectoral and pelvic fins form a powerful suction cup that allows it to cling to rocks and survive in torrent-like flows that would sweep away most other fish. Reaching a maximum size of around 5.7 cm (2.2 in), it is a peaceful, social species that should be kept in groups of at least three to five individuals in a tank of 60 L (15 gal) or larger.

This species demands excellent water quality and very high oxygen levels. The aquarium must be well-established with strong water movement — ideally 10–15 times turnover per hour — provided by powerheads or an oversized filter. A rounded gravel or sand substrate with smooth water-worn stones, driftwood, and bright lighting promotes the growth of biofilm and algae, which form the bulk of their natural diet. Water temperature should remain cool at 18–24°C with pH 6.5–7.5; they struggle in warm, stagnant conditions.

Sewellia lineolata is primarily a grazer of biofilm and soft algae, and a mature tank with naturally colonised surfaces is essential for long-term health. Supplement with high-quality sinking algae wafers and occasional live or frozen foods such as brine shrimp and bloodworm in moderation. They are compatible with other peaceful, cool-water species such as white cloud mountain minnows, small Danio species, and other hillstream loaches but should not be kept with large or aggressive fish. Breeding is uncommon but possible in spacious, well-oxygenated setups.