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The Gastromyzon lineolata, also sold under the names Sewellia and Borneo Loach, is a small rheophilic loach adapted to tropical streams in Borneo. Its flattened body and sucker-like pectoral and pelvic fins allow it to remain firmly attached to rocks despite strong current. This species is considered very common in the aquarium trade, but it is still demanding when it comes to water quality. It is best kept in a mature, highly oxygenated aquarium with steady flow, mineral surfaces covered in biofilm and peaceful tank mates.

General description

The Gastromyzon lineolata belongs to the family Gastromyzontidae, a group of loaches specialized for life on rocky bottoms and in flowing water. It is a peaceful bottom-dweller, usually seen resting on stones or moving in short bursts from one surface to another. Its most notable adaptation is its adhesive ventral disc, formed by the pectoral and pelvic fins, which helps it withstand current. In aquariums, it is generally active during the day, especially when algae and biofilm are available. It should be kept in a group and provided with several rocky shelters.

Geographical origin and habitat

Country of reference: Malaysia, on the island of Borneo, in the state of Sabah. The species inhabits clear, cool and highly oxygenated forest streams with steady to fast current. The bottom is generally made up of pebbles, slabs and larger rocks covered by a thin layer of algae and microorganisms. Aquatic vegetation may be sparse, while dense streamside vegetation provides shade. Water depth remains shallow, often from a few centimetres to less than one metre depending on the season. An aquarium designed around this habitat should emphasize water movement rather than dense planting.

Precise location and local name

The Gastromyzon lineolata is associated with waterways in Malaysian Borneo, particularly Sabah. Precise local names vary among communities and are not commonly used in the aquarium trade. Internationally, it is most often sold as Borneo Loach, while Sewellia is also used, although that name normally refers to another genus of stream loaches. To avoid confusion, the scientific name should be checked on the label or with the supplier. This species is widely available in aquaria and is not considered rare in the general trade.

Appearance and physical characteristics

The body of the Gastromyzon lineolata is short, flattened and shaped for adhesion to surfaces exposed to current. Its base colour ranges from beige to olive brown, with dark longitudinal and irregular markings that break up its outline. The pectoral and pelvic fins are broad and help it remain attached to rocks. The mouth is positioned underneath the head and is adapted for grazing surfaces. Adult size remains small, reaching about 5 cm at most. As in many stream loaches, its body is designed more for stability and adhesion than for prolonged open-water swimming.

General diet

The Gastromyzon lineolata mainly grazes on the natural biofilm that develops on rocks, glass, wood and other illuminated surfaces. This biofilm contains algae, bacteria and tiny organisms. In a new or overly clean aquarium, this resource may be insufficient, so the fish should preferably be added to a mature system. Supplement its diet with vegetable wafers, algae-based tablets and small portions of soft or frozen foods. Meals should remain moderate, since this species is not simply a waste eater. A varied diet and healthy algae growth are essential.

Essential data

• River of origin: Waterways of Malaysian Borneo, particularly within the Sabah drainage
• Local name used: Borneo Loach in the trade; Sewellia is also used but may cause confusion
• Origin of the scientific name: The genus name Gastromyzon and the epithet lineolata
• Meaning of the full name: Gastromyzon comes from the Greek gaster, belly, and myzon, sucking or adhering; lineolata means marked with small lines
• Common or vernacular names: Borneo Loach, Sewellia, Borneo hillstream loach
• Family: Gastromyzontidae
• Subfamily: No commonly recognized subfamily
• Name pronunciation: gas-tro-MY-zon - lin-ee-oh-LAH-ta
• Discovery: Tyson R. Roberts, 1982
• Maximum adult size: Approximately 5 cm
• Water temperature and pH: 20 to 24 °C; pH 6.5 to 7.5
• Stream appearance and surrounding vegetation: Clear, shallow, fast-flowing and shaded stream, with biofilm-covered rocks and dense bank vegetation
• Typical tank mates: Other Gastromyzon, Beaufortia, Pseudogastromyzon, small stream loaches and other peaceful rheophilic fish
• Temperament and behaviour: Peaceful, social, active on rocks and generally diurnal
• Water depth: Shallow, from a few centimetres to less than one metre
• Sexual dimorphism: Females are often broader; differences are difficult to see in juveniles
• Bottom structure and flow: Pebbles and rock slabs, sustained to fast current and high oxygenation

In your aquarium

To succeed with the Gastromyzon lineolata, set up a mature aquarium with smooth rocks, constant flow and highly oxygenated water. Efficient filtration, regular water changes and biofilm that is continuously available are priorities. Avoid boisterous tank mates, high temperatures and sterile systems. A well-fed group, suitable current and several resting areas will allow this small loach to display natural behaviour and maintain good long-term condition.