Gastromyzon monticola

Gastromyzon monticola is a small loach with a unique body shape for life in fast currents. The body and head are strongly flattened, and the pectoral and ventral fins are positioned horizontally and partially fused to form a powerful sucker disc. This allows the fish to grip firmly to rocks and move across them. Adults reach 7–8 cm in length. Sexual differences are subtle, but females are usually larger with a broader body, visible from above.

The species is endemic to Borneo: it is known only from streams in Malaysian Sabah—rivers flowing into Marudu Bay and the Wario River system descending from Mount Kinabalu slopes. In nature it inhabits the upper reaches of mountain rivers and streams with fast flow, clear water, and high oxygen content. It prefers areas with stony or pebble beds where a rich biofilm of algae and microorganisms covers the rocks. Fish typically stay in zones with moderate or strong flow, holding position behind or on vertical surfaces of boulders.

This is a peaceful but territorial species. Intraspecific squabbles over the best feeding spots are common, but they rarely result in injury. In an aquarium, keeping a group of 4 or more individuals is recommended, allowing you to observe their natural social behaviour. The species is primarily bottom-dwelling and active during the day. It is well compatible with small schooling fish occupying the middle and upper layers, as well as with other inhabitants of fast streams.

A tank of at least 100 litres is needed with strong aeration and powerful filtration to maintain high water flow. Rounded pebbles and large rocks that develop algae over time work best as substrate. Lighting should be bright enough to stimulate biofilm growth. A tight-fitting lid is essential, as these fish can move across glass surfaces and may leave the tank. Water parameters: temperature 20–24 °C, pH 6.0–8.5, water hardness 2–12 dGH.

In nature the fish feeds primarily on algae and microorganisms scraped from rocks. In an aquarium the diet should include quality dry foods and frozen or live foods (artemia, bloodworm). Avoid excess protein, as this can cause digestive problems. Use specialized plant-based foods and ensure rocks with natural algae growth are present in the tank.

Breeding in an aquarium is possible under suitable conditions. Spawning occurs on stony substrate. The eggs are small and non-adhesive, settling in crevices between rocks. The fry are extremely tiny and require abundant microorganisms (infusoria) in the first days of life. Successful breeding requires stable conditions with good water quality and shelter among large gravel for the young.

The species is sensitive to low oxygen levels and organic pollution. Bacterial or parasitic infections (for example, flagellates) occur under poor conditions. Prevention consists of maintaining high water cleanliness, regular water changes, and ensuring active circulation. When treating, account for the fish's high sensitivity to some medications and salts.

When buying, choose active fish that show interest in foraging on rocks and glass. Avoid individuals showing signs of starvation, sunken bellies, or damaged fins. Healthy fish should grip surfaces firmly and have no white coating or spots on the body. It is worth asking what the fish was fed at the shop to ease adaptation to the new diet.