Gastromyzon monticola

Gastromyzon monticola is a small fish from the family Balitoridae, possessing a unique morphology for life in fast-flowing currents. The body and head are greatly flattened, and the pectoral and pelvic fins are positioned horizontally and partially fused, forming a powerful suction disc. This allows the fish to firmly attach to rocks and move across them. Adults reach 7–8 cm in length. Sexual dimorphism is subtle, but females are typically larger and have a wider body, which is noticeable when viewed from above.

The species is endemic to the island of Borneo: it is known only from watercourses in the Malaysian state of Sabah — streams emptying into Marudu Bay and the Wariu River basin, all of which drain Mount Kinabalu. In nature, it inhabits the headwaters of mountain rivers and streams with fast currents, clean, and oxygen-rich water. It prefers areas with a rocky or gravel bottom, where a rich biofilm of algae and microorganisms forms on the surface of the stones. The fish often stay in zones with moderate or strong currents, occupying spots behind boulders or on their vertical surfaces.

This is a peaceful but territorial fish. Intraspecific skirmishes for the best feeding spots are common, but they rarely result in injuries. In an aquarium, it is recommended to keep a group of 4 or more individuals to observe their natural social behavior. The species is primarily bottom-dwelling, active during the day. It is well compatible with small schooling fish that occupy the middle and upper water layers, as well as with other inhabitants of fast-flowing streams.

For keeping, an aquarium of at least 100 liters is required with strong aeration and powerful filtration, ensuring a high water flow rate. Rounded pebbles and large stones, which will eventually be covered with algae, are best used as substrate. Lighting should be bright enough to stimulate biofilm growth. A tight-fitting lid is essential, as the fish can move along the glass and may leave the aquarium. Water parameters: temperature 20–24 °C, pH 6.0–8.5, hardness 2–12 dGH.

In nature, it feeds primarily on algae and microorganisms scraped from rocks. In the aquarium, the diet should include high-quality dry foods, frozen or live foods (brine shrimp, bloodworms). It is important to avoid an excess of protein-rich food, as this can cause digestive problems. It is recommended to use specialized plant-based foods and ensure the presence of rocks with natural algal growth in the aquarium.

Breeding in an aquarium is possible if suitable conditions are provided. Spawning occurs on a rocky substrate. The eggs are small, non-adhesive, and settle in crevices between stones. Fry are very small and require an abundance of microorganisms (infusoria) in the first days of life. Successful breeding requires a stable environment with good water quality and the presence of hiding places for offspring among large gravel.

The species is sensitive to low oxygen levels and organic water pollution. Infections caused by bacteria or parasites (e.g., flagellates) are common under poor keeping conditions. Prevention involves maintaining high water purity, regular water changes, and ensuring active circulation. When treating, the high sensitivity of the fish to certain medications and salts should be considered.

When purchasing, choose active fish that show interest in foraging on rocks and glass. Avoid individuals with signs of emaciation, sunken bellies, or fin damage. Healthy fish should firmly attach to surfaces and not have whitish coatings or spots on their bodies. It is recommended to inquire about what the fish were fed in the store to facilitate adaptation to a new diet.