Fish atlas

Geographical Origin and Habitat: Endemic to the Pearl River basin and numerous mountainous coastal rivers in Guangdong province and Hong Kong, southern China. Inhabits exclusively crystalline mountainous 'hillstreams', where water flows immensely fast forming freezing rapids, and where the rocks are covered by a velvety carpet of 'Aufwuchs' (algae and associated microorganisms).

Taxonomy and Morphology: Gastromyzontidae family. Its body (about 5.5 - 6 cm / 2.2-2.4 inches) is the pinnacle of hydrodynamics: it is flattened into a lens or disc shape, with enormous pectoral and pelvic fins expanded laterally to form a giant 'suction cup'. This seals its body to flat stones, allowing it to withstand terrifying water flows without wasting muscular energy.

Social Behavior: Not a tight schooling fish, but requires aggregation (groups of 4-6) for interactions. Highly territorial over food patches. Males challenge each other in hilarious, bloodless rocky 'pancake fights': they lift each other up, trying to peel the opponent off the stone by covering its back. Totally peaceful toward fish swimming in the upper water column.

Coloration and Sexual Dimorphism: Camouflage yellowish-brown/olive base color, studded with a dense network of black and brown spots or specks on the back and fins. The dorsal fin is distinctive: a deep scarlet red margin framed in black. Females are noticeably plumper and wider when viewed from above; males develop showy breeding tubercles (little 'horns') along the fleshy snout and pectoral fins.

Aquarium Setup: Demands a specialized aquarium, the famous 'River-Manifold' or 'Hillstream Setup'. Minimum size 80-90 cm (32-36 inches). Background and floor composed of massive, smooth, flat river pebbles. EXCEPTIONALLY STRONG lighting to promote the growth of soft green algae and diatoms on the stones (their pasture). An oversized additional powerhead (e.g. 2000 l/h) sweeping the rocks with a linear, roaring flow is indispensable.

Diet and Feeding: Aufwuchs grazers. Their flat belly and tiny half-moon ventral mouth equipped with horny 'teeth' serve to scrape epilithic algae and biofilm from smooth stones. In sterile, new aquariums, they will starve to death. They require natural green algae, supplemented by Repashy bottom-scratcher gel (smeared on stones and allowed to dry), spirulina wafers, and small thawed bloodworms.

Water Quality: TEMPERATE/SUBTROPICAL FISH. HEAT SUFFOCATES THEM. The ideal temperature is 20-24°C (68-75°F) (tolerates short summer spikes only with monstrous aeration). They have microscopic gills and depend on violent currents to push oxygen through. They do not need soft Amazonian water: pH 6.5 - 8.0 and medium hardness (GH 5-15) are perfect. Zero pollutants tolerated.

Compatibility and Cohabitation: Perfect roommates for a cold hillstream aquarium with White Cloud Mountain Minnows, Zebra Danios, other river loaches (Sewellia, Gastromyzon), or Rhinogobius. Absolutely NOT to be kept with classic Plecostomus or Ancistrus (Bristlenose plecos), which, due to their size, would eat all the algae, starving the Hillstream Loaches.

Aquarium Breeding: Possible in mature tanks. The male digs a small spawning crater under a rounded stone by displacing fine gravel. If the water flow is excellent for oxygenation, some juveniles will mysteriously appear weeks later.

Risks and Diseases: 1. Lethal thermal suffocation if placed in typical stable tropical tanks at 28°C (82°F) without water movement. 2. Lethal starvation in pristine, design-perfect aquariums lacking mature algal slime.