Gastromyzon viriosus

Overview

The sturdy Gastromyzon viriosus has complete pale body bars and fine head reticulation against a dark brown background. Occasionally imported with other hillstream fishes, it requires a mature flowing aquarium with ample oxygen and grazing resources.

Distribution & habitat

Its known range is the Tatau catchment in central Sarawak, Malaysian Borneo. The type site is the Sawi River in Tatau District, Bintulu Division.

Members of the genus typically occupy shallow, clear, oxygen-rich streams. Algae and microscopic organisms coat the rocky bottom. Fish face the current beside, behind, or beneath stones, while aquatic vegetation is often scarce.

Aquarium setup

Begin with approximately 75 × 30 cm of floor space. Arrange smooth stones of varied sizes over sand or gravel. Ample filtration, circulation, and supplementary aeration should maintain cleanliness and oxygen; turnover around ten to fifteen aquarium volumes hourly is suggested. Oxygen supply deserves particular attention in warmer conditions.

Strong illumination supports grazing surfaces. Weathered wood is usable, but heavy staining from fresh wood can reduce useful light. Hardy plants and exposed filter sponges provide additional feeding surfaces. Use only a mature aquarium, change water regularly, and retain established growth on most rocks. Glass-climbing ability calls for a secure lid.

Diet & feeding

Algae and associated microscopic life probably form much of the natural diet. Prepared foods and live or frozen bloodworms are accepted, but excessive animal protein may cause internal problems. Vegetable-rich gel foods with spirulina can supplement grazing.

Maintain abundant mature surfaces. If necessary, grow algae on stones in another brightly lit container and rotate them into the aquarium. Diatoms and soft green growth are more useful than tough brush algae. Thin arrivals need continuous suitable food without competition until condition improves.

Behaviour & compatibility

Peaceful behavior does not protect this fish from much larger, aggressive, or highly competitive companions. Suitable small open-water cyprinids, stream gobies, and catfish may be considered. Compatibility of other loaches needs individual assessment.

The genus forms loose aggregations; groups of at least four are recommended. Some individuals defend favored feeding patches more strongly than others.

Sexual dimorphism

Mature females are distinctly fuller-bodied and often slightly larger. Comparison from above or below makes the difference clearer.

Breeding

Captive spawning has not been recorded for this species. Reports of reproduction or spontaneously appearing fry in relatives provide comparative context, not an established breeding procedure for this fish.

Notes

Eight to ten cream bars continue across the flanks, accompanied by fine pale head reticulation, a rounded snout in dorsal view, and an angular gill opening. These characters are more informative than broad Borneo-sucker trade labels.