The Harlequin Shark, scientifically known as Labeo cyclorhynchus, is a distinct and visually striking freshwater fish native to the Congo River basin in Africa. This species is appreciated for its unique appearance among aquarium enthusiasts but is known to present some challenges in terms of care and compatibility with other fish.

The Harlequin Shark has a slender, elongated body with a high contrast color pattern that makes it stand out in any aquarium setting. The base color of the body is typically dark, ranging from deep brown to almost black, with bold white or cream-colored markings that cover the fins and part of the body, giving it the 'harlequin' appearance it's named for. Another distinctive feature is its snout, which is slightly upturned and gives the fish a unique profile.

Despite its appealing appearance, the Harlequin Shark is known for its territorial behavior, especially as it matures. It tends to become more aggressive towards other bottom-dwelling fish, making it a challenging species to incorporate into a community tank. To minimize territorial disputes, it's recommended to provide plenty of space and hiding places such as caves, driftwood, and dense plantings. This allows the Harlequin Shark and other tank inhabitants to establish their own territories and retreats.

In terms of care, the Harlequin Shark thrives in well-filtered, clean water with moderate flow, mimicking the conditions of its natural riverine habitat. The water temperature and pH should be maintained within the species' tolerance range to promote good health. Regular water changes are essential to keep nitrate levels low and ensure the overall well-being of the fish.

Diet-wise, the Harlequin Shark is omnivorous but shows a preference for vegetable-based foods. A balanced diet should include high-quality sinking pellets or wafers formulated for herbivorous fish, supplemented with occasional offerings of live or frozen foods for protein. Vegetable matter, such as blanched spinach or zucchini, can also be offered to ensure a varied and nutritious diet.

Breeding the Harlequin Shark in captivity is rarely reported, likely due to the specific environmental conditions required for spawning and the species' territorial nature. Those interested in breeding this fish would need to mimic seasonal changes and provide an optimally designed habitat to encourage reproductive behaviors.

Overall, the Harlequin Shark is best suited for experienced aquarists who can meet its specific care requirements and manage its territorial tendencies. When properly cared for, this species can be a captivating and rewarding addition to a suitably designed aquarium, offering a glimpse into the diversity and beauty of African riverine fish.