The Harlequin Shark (scientifically valid as Labeo cyclorhynchus, though commonly sold as L. variegatus) is a highly territorial, bottom-dwelling cyprinid native to the Congo River basin. Famous for the spectacular cream and black mottling of juveniles, their colors sadly fade to a darker tone as they mature. They are voracious algae and aufwuchs grazers that require high water flow, smooth substrate to protect their delicate barbels, and must absolutely be kept as a solitary specimen due to their extreme intolerance of conspecifics and other bottom-dwellers.
Harlequin Shark At a Glance
Harlequin Shark Tank Requirements
Will Harlequin Shark fit in your tank?
Care guides tell you what Harlequin Shark needs, the next question is whether your tank can safely provide it. Test Harlequin Shark against your tank size, maintenance needs, and the fish you already keep before you buy.
Useful setup supplies
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Harlequin Shark Water Parameters
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Harlequin Shark Temperament & Compatibility
Harlequin Shark Varieties
Each variety inherits the species defaults above. Only differences are highlighted.
Standard (Adult)
The mature form. Their vibrant juvenile colors fade to a darker grey/black. They are relentlessly territorial toward similar species and must be kept as a solitary bottom dweller in a spacious tank.
Same care requirements as the base species
Also known as: Adult Harlequin Shark, Wild Type
Juvenile
Displays the magnificent contrasting colors that make the species popular in the aquarium trade. While smaller and slightly more shy, they still require adequate space and will quickly develop aggressive tendencies as they grow.
Differs in 5 traits from base species
Also known as: Baby Harlequin Shark, Juvenile
Harlequin Shark Care Guide Summary
The Harlequin Shark, scientifically known as Labeo variegatus, belongs to the Cyprinids family group. Adults reach a maximum size of approximately 16 cm and have a fusiform body shape with a moderate growth rate. Classified as aggressive, this species primarily occupies the bottom zone of the aquarium and produces a medium level of biological waste.
To thrive, the Harlequin Shark requires a freshwater only aquarium with a minimum volume of 150 litres and a tank length of at least 120 cm. Water temperature should be maintained between 21°C and 27°C, with a pH range of 6–7.5 and a general hardness of 3–15 dGH. A high water flow is preferred.
Due to its specialist needs, the Harlequin Shark is best suited for fishkeepers who can provide a carefully planned setup. This species is available in 2 varieties: Standard (Adult) and Juvenile. Each may differ slightly in size, temperament, or care needs, so it is worth checking the specific requirements of the variety you plan to keep.
Harlequin Shark Habitat Setup
When setting up an aquarium for the Harlequin Shark, a high water flow best suits their natural preferences. Because this species occupies the bottom zone, the aquarium layout should prioritise sufficient floor space with hiding spots among rocks, wood, or dense planting. Useful additions include a sand substrate to accommodate their sifting behaviour, driftwood, which can serve as both a hiding place and a dietary supplement, and an established tank with natural algae growth, as they depend on it as a primary food source.
Harlequin Shark Compatibility Notes
Classified as aggressive, the Harlequin Shark is best housed alone, as they do not tolerate others of their kind in confined spaces. When choosing tankmates, conspecific aggression can be intense, especially in smaller tanks, territorial behaviour may cause issues if hiding spots or floor space are limited, and their energetic swimming style may stress more sedentary or timid species. Selecting tankmates that favour different water layers from the bottom zone can help reduce competition and territorial overlap.
Harlequin Shark Recommended Tank Sizes
Standard aquarium sizes that meet the minimum volume and length requirements for Harlequin Shark.
55 Gallon Standard
60 Gallon Breeder
75 Gallon Standard
90 Gallon Standard
125 Gallon Standard
150 Gallon High
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Frequently Asked Questions About Harlequin Shark
How big does Harlequin Shark get?
Harlequin Shark (Labeo variegatus) typically reaches a maximum adult size of approximately 16 cm. They have a fusiform body shape and a moderate growth rate.
What tank size does Harlequin Shark need?
A minimum aquarium volume of 150 litres and a tank length of at least 120 cm are recommended for Harlequin Shark. This ensures enough swimming space and helps maintain stable water conditions.
What water parameters does Harlequin Shark need?
Harlequin Shark thrives in freshwater only conditions with a temperature range of 21–27°C, a pH between 6 and 7.5, and a general hardness of 3–15 dGH. A high water flow is preferred.
Is Harlequin Shark peaceful or aggressive?
Harlequin Shark is classified as aggressive with an aggression score of 8 out of 10. Careful tankmate selection is essential to avoid conflict.
Can Harlequin Shark live with others of its kind?
No. Only one Harlequin Shark should be kept per tank. Keeping multiples in the same aquarium typically results in aggression and stress.
Does Harlequin Shark have any special tank requirements?
Yes. Harlequin Shark benefits from sand (sifters), driftwood (digestion/hiding), and established algae (otocinclus) in the aquarium. These features help replicate their natural habitat and promote overall health and well-being.
Plants That Suit Harlequin Shark
These plants pair well with Harlequin Shark based on shared water preferences, layout fit, and how likely they are to hold up in the same aquarium.
African Water Fern
Bolbitis heudelotii
Boivin's Aponogeton
Aponogeton boivinianus
Capuron's Aponogeton
Aponogeton capuronii
Madagascar Lace Plant
Aponogeton madagascariensis
African Onion Plant
Crinum calamistratum
Afzel's Anubias
Anubias afzelii
Fish Similar to Harlequin Shark
Harlequin Rasbora
Trigonostigma heteromorpha
A highly popular, peaceful schooling fish recognizable by its metallic copper/orange body and the distinct black triangular 'porkchop' patch on its hindquarters. Originating from peat swamps and blackwater streams in Southeast Asia, they are active swimmers that thrive in heavily planted aquariums with gentle to moderate water flow.
Red Tailed Black Shark
Epalzeorhynchos bicolor
A striking and highly active bottom-dwelling cyprinid known for its jet-black body and vibrant red tail. While beautiful, they are notoriously territorial, especially toward their own kind, similar-looking species (like Rainbow Sharks), and sometimes other bottom-dwellers. They must be kept as the only 'shark' in the tank and require a large footprint with plenty of caves and broken sightlines.
Bala Shark
Balantiocheilos melanopterus
Despite its name, the Bala Shark is a peaceful, schooling cyprinid. They are extremely active, fast swimmers that grow very large and startle easily. They are notorious for injuring themselves by crashing into the aquarium glass if kept in small tanks or easily spooked. They must be kept in groups and eventually require massive, custom-sized aquariums.
Rainbow Shark
Epalzeorhynchos frenatum
A popular, active freshwater 'shark' (actually a cyprinid) known for its striking red fins contrasting with a dark or albino body. They are highly territorial bottom-dwellers. Only keep one per tank, as they are notoriously aggressive toward their own kind, other 'sharks' (like the Red Tail Shark), and similar-looking bottom feeders.
Loricaria lundbergi
Loricaria lundbergi
A slender, highly camouflaged whiptail catfish native to the deep, blackwater river channels of the Rio Negro and Rio Madeira basins. Unlike many suckermouth catfish, they are primarily insectivores and detritivores, actively sifting through the substrate for aquatic insect larvae rather than eating algae. They are peaceful, facultative air-breathers that require a soft sand substrate to prevent damage to their delicate mouths.
Freshwater Harlequin Shrimp (Sulawesi)
Caridina cf. spongicola
An expert-level, tiny freshwater shrimp endemic to Lake Towuti in Sulawesi. Known for its striking red and white bands and shy nature. In the wild, they live symbiotically with a specific freshwater sponge, though in aquariums they can be sustained on mature biofilm. They require extremely stable, warm, alkaline water parameters and should only be kept by advanced aquarists.