The Mottled Hillstream Loach, scientifically known as Sewellia sp. “Spotted SEW01,” is a captivating freshwater fish native to the fast-flowing, oxygen-rich streams of Southeast Asia. This species is admired for its unique adaptations to strong currents, striking patterns, and peaceful demeanor, making it a fascinating choice for aquarists who enjoy naturalistic river-style setups. SEW01 has a flattened, elongated body with broad pectoral and pelvic fins that allow it to cling securely to rocks and resist strong currents. Its coloration is a complex mosaic of earthy browns and cream tones, often forming mottled spots or intricate patterns across the body and fins. This camouflage not only gives it a visually appealing appearance but also helps it blend into rocky streambeds, reflecting its natural habitat. The fins are often subtly patterned as well, providing additional elegance when the fish moves gracefully across stones or rests in the flow. In the aquarium, the Mottled Hillstream Loach thrives in conditions that mimic its native environment. A substrate of smooth rocks, pebbles, or sand is ideal, along with ample water flow to simulate stream currents. High oxygenation and clean, well-filtered water are crucial for maintaining their health. Adding driftwood, leaf litter, and hardy plants such as Anubias or Java fern can create shaded areas and resting spots, though open rock surfaces are essential for grazing and movement. This species is peaceful and best kept in small groups, as social interactions help reduce stress and encourage natural behavior. They coexist well with other gentle, current-loving species such as small danios, rasboras, and other hillstream loaches. Watching them cling to rocks, glide in the current, and forage for biofilm is both engaging and calming. Feeding should focus on the natural diet of algae and biofilm that they graze from surfaces. In the aquarium, this can be supplemented with algae wafers, blanched vegetables such as zucchini or spinach, and small amounts of protein foods like frozen daphnia or bloodworms. Offering a variety of foods ensures they remain healthy, active, and vividly patterned. Breeding Sewellia sp. “SEW01” in captivity is not well-documented and is considered challenging. Like other hillstream loaches, they may require very specific water flow, temperature, and environmental cues to encourage spawning. Most individuals in the hobby are therefore maintained for their beauty and behavior rather than reproduction. The Mottled Hillstream Loach is an excellent choice for aquarists seeking a small, peaceful, and highly specialized species. Its intricate patterns, flowing movements, and river-adapted lifestyle make it a remarkable addition to well-oxygenated, carefully arranged aquariums that replicate the serenity and dynamics of natural streams.