HARLEQUIN SHARK - Aquarium Advice and Care Sheet

HARLEQUIN SHARK – Aquarium Advice and Care Sheet

Just like most other so-called aquarium sharks, the Harlequin shark (Labeo cyclorhychus) is a freshwater fish species from the Family Cyprinidae.

Most Aquarium hobbyists desire this fish because of its attractive body patterns. The aquarium hobby also recognizes this fish as harlequin sharkminnow or variegated shark. The latter name goes with the description of this species by Pellegrin (1901) as Labeo variegatus.

The Harlequin shark is a central African fish that will make your fish tank look special. Certainly, you will enjoy your “shark” keeping hobby with this species. Especially, if you learn to keep it happy always.


Harlequin Shark Scientific Classification

Kingdom: Animalia

Phylum: Chordata

Class: Actinopterygii

Order: Cypriniformes

Family: Cyprinidae

Sub-family: Labeoninae

Genus: Labeo

Species: L. cyclorhynchus

Binomial Nomenclature: Labeo cylorhynchus

The Harlequin Shark Appearance

The Harlequin shark has a base body color of creamy yellow with grey markings and black blotches. Further, the black blotches extend to their translucent fins.

As juvenile fish, they have the most intense coloration and markings. However, these colors that make the Labeo cyclorhynchus stand out fade as it attains maturity.

They have an elongated body and stiff fins just like other shark species from its family. This is what marks their vague resemblance to the true sharks.

This shark species have 12 soft rays on their dorsal fin with a prominent curve on the upper edge.

They possess rows of transverse ridges of tissues in their lips making their lips thick. Also, they have two pairs of barbels (Whisker-like sensory organs) well-developed for sensation.

Both the male and female Harlequin shark have a similar appearance. As such, there is nothing much to differentiate them with except that in spawning conditions the females develop thicker bodies than the male that will always look slender.

This freshwater shark species will usually grow to a maximum size of about 16 inches (40.6 cm).

Habitat and Distribution in Nature

The Harlequin shark is an indigenous species to the middle and lower Congo River basin of the Republic of Congo and the Democratic Republic of Congo.

They are also extant in the Ubangui River in the Central African Republic and Ogowe (spelled ‘Ogooue’ at times) River in Gabon.

The region of Congo stands as a center of diversity for the Genus Labeo. As a result, there are over fifteen different species native to the waters within this region. Thus, forming a subgroup of monophyletic species within the Genus.

The habitat of the Harlequin shark is usually forest streams mostly characterized by thick marginal vegetation. Often times, there is a shade provided by thick rainforest in the form of a canopy above these waters.

At the bottom of these forest streams lies a substrate of a thick layer of silt littered with fallen tree branches and leaves. The water may have a color of weak brown resulting from tannins being released from organic matters decomposing. However, it is still quite clear looking at it.

Behavior in Nature

The Harlequin shark is an omnivorous fish species. Their source of food comprises mainly of aufwuchs, which includes algae and microfauna. They get this from growth at the bottom of the waters.

As an adult, these fish species are aggressively territorial. Consequently, they prefer to be in solitude. They do not socialize but prefer to secure a territory where they do not allow others except during the season they spawn.

However, juvenile sharks are not as territorial as adults. Instead, they hide most of the time.

Human use and Conservation

Locally, these fish species serve as a source of food to the people. Also, it is being collected for the aquarium trade.

There has not been any breeding of the Labeo cyclorhynchus in aquarium settings. This is due to its solitary and aggressive nature. Thus, available in the aquarium trade are only specimens collected in the wild.

The conservation status of this shark species according to the IUCN redlist as ‘Least Concern’.

There is no major activity yet known to threaten its existence in nature. More so, the habitat where it is still extant is widespread in the Congo region.

The Harlequin Shark as an Aquarium Pet

Most aquarium hobbyists who go for this shark species do so because of their unusual but attractive body coloration. But, some do not know what to expect while keeping this fish in captivity.

In line with this, special attention should be paid to the tank size, tank mates, and tank decorations. Certainly, this freshwater shark is very aggressive and territorial as well.

These fish are so mean! Therefore, we do not recommend it for beginner hobbyists. Instead, any shark keeper that would keep this species happily in an aquarium must have a strong prior experience of shark keeping.

Tank Conditions

In a Glance

  • Max. Size : 6 inches (15.2 cm).
  • Size of Tank Required: 55 gallons and above.
  • Suitable Tankmates: a relatively large fish that swims fast. Also with a temper as the Harlequin. For example, minnows, carps, danios, and barbs.
  • Optimal Tank Temperature: 72 to 82 F.
  • Water Ph: 6.5 to 7.5
  • Water Hardness: 3 – 15dGH
  • Diet: Omnivore
  • Temperament: Aggressively Territorial
  • Expected Lifespan: 4 to 6 years
  • Minimum Aquarist Experience Level: Intermediate

Size of Tank Required to Keep the Harlequin Shark

Choosing a tank for your Harlequin shark may not be the biggest challenge in keeping this species of aquarium fish. This is because while this shark might grow substantially large up to 16 inches (40.6 cm) in the wild, they would only attain about 6 inches (15.2 cm) in captivity.

This includes them in the list of the smallest sharks you can keep in your aquarium. More so, they do not require a community tank due to their territorial and aggressive nature. And, they would never tolerate their own species. Thus, they are better kept alone and in solitude instead of in shoals.

As a result of these, you can choose a tank of 55 gallons to keep your Harlequin shark. This can keep them until adulthood. Although, you can make use of a larger tank to increase space, especially when considering tank mates for your pet shark.

Aquarium Decoration

Having an idea of the natural habitat of the Harlequin shark would help you to choose the best aquascape for your pet shark. Thus, you need to densely plant the tank to keep this species.

For the substrate, make use of silt or round rocky gravel of varying sizes. Rocks with sharp edges such as lava rock may injure your shark since they are bottom-dwellers and have delicate mouthparts and barbels. As such, you must avoid them.

Add some driftwood branches and small boulders. Create as many nooks and crannies in the tank as possible. These will serve as hiding places for your pet shark. Of course, they would make the most use it as juveniles hiding the majority of the time.

You can also grow and attach hardy plants such as Java fern, Bolbitis, or Anubias on the driftwoods or rocks to promote algae growth and biofilm. The Harlequin sharks will naturally graze on these.

Compatible Tank Mates for Your Harlequin Shark

Most aquarists would prefer to keep the Labeo cyclorhynchus in a single-species aquarium with no tank mates. Of course, this is due to the challenge encountered in keeping them with other species.

This shark in the aquarium is very aggressive and territorial and would eventually harm anything that gets too close to it. As such, any compatible tank mate should spend most of its time in the middle or top level of the tank.

Not only that, but they should also be fast swimmers with similar temperament as the Harlequin shark. At least, they can keep themselves safe.

Examples of compatible tank mates include species of larger barbs, carps, danios, and minnows.

Do not make the mistake of keeping this fish together with its kind or any species with similar body shape. They are so intolerant of their species and will definitely tear themselves apart.

While keeping the Harlequin shark with tank mates, make sure to watch out for any signs of aggression and transfer them before any harm is done. If not, leave them alone in the tank.

Suitable Tank Water Condition for the Harlequin Shark

To keep your pet shark healthy and happy, you need to prepare the water you keep them in to meet some specific conditions. That is to say, you must consider the temperature of the tank, the pH level, level of water movement, and the lighting condition as well.

To set up the water conditions properly, keep in mind the water condition of their natural habitat. Thus, we recommend the following conditions:

Water Temperature

The Harlequin shark is most comfortable in tropical freshwater with temperatures ranging from 72 to 82F.

A basic thermometer will help you achieve the desired tank temperature all the time.

Water pH Level

Keep the pH level of the tank within a range of 6.5 to 7.5. In shark keeping the ability to maintain the desired pH level of the water is very crucial.

This is because a slight deviation from the recommended range can lead to serious health implications for your pet shark. Therefore, always keep an eye out for changes in your tank pH level. And, be careful of the things you introduce into the tank that might cause changes in pH condition.

Range of Water Hardness

Keep your Harlequin shark in the water with a hardness of range 3 – 15dGH (degree of General Hardness). From the water hardness table, this means soft water ranging to medium-hard water.

Water Current and Filtration

Make sure to install a powerful filter and maintain a good water flow rate in the tank you keep your Harlequin shark. Of course, this is a River-dwelling fish and would love to swim against the water current.

Tank Lighting

We recommend you introduce relatively bright light. And, let it shine for longer periods. At least, this will encourage algal growth which the Harlequin shark will graze upon.

Apart from this, there is no specially recommended lighting condition for your pet shark.

Note: to meet with all the recommended water conditions for your Harlequin shark tank, you will need to acquire a basic water testing kit. And, constantly check to ensure everything is working right.

Food for the Harlequin Shark

The Harlequin shark is an omnivorous species and will eat almost anything you place into the tank.

When you keep this species in your tank offer them regular meals consisting of live frozen or freeze-dried food materials such as bloodworms, brine shrimp, mosquito larvae, and daphnia. Also, mix the diet with quality flake foods, algae wafers, sinking granules, and a lot of vegetable matter.

Occasionally include blanched spinach, finely chopped fruits, cucumber, and shelled peas to your Harlequin shark’s diet. This will help to improve their color.

These shark species are bottom-feeders and will swim around the floor of the tank in search of food. Most of the time, they will graze upon the algae growing in the tank with their fleshy mouth.

Due to the grazing habit of the Harlequin shark, use plants with robust nature in the tank. This is so they can withstand constant nibbling from this shark species.

Sexing and Reproduction

Labeo cyclorhynchus breeds naturally in their native habitat. There are currently no reports of captive breeding of these species. And, it is unlikely to be possible. This is due to the solitary lifestyle of adult sharks. And of course, their aggressive nature toward their kind.

This aggression is most visible within the confines of a home aquarium. Thus, making it practically impossible to keep a group of these species in a tank.

Even in large public aquaria where these fish species are on display, you will likely see them with tattered fins showing the level of their incompatibility.

As such, all of the Harlequin sharks available in the aquarium trade are collected from their natural habitat.

Threat to Human

The Harlequin shark is actually harmless to humans. However, do not go dipping your hand into its tank as it may mistake you to be food.

Once the necessary tank conditions for keeping this shark species is met, you would not really notice their aggressive behavior. Thus, if the shark is happy, you will be happy with your aquarium as well.

Points to Keep in Mind

To have peace in your tank with the Harlequin shark and other tank mates, make sure to introduce the tank mates first and the Harlequin shark last. By so doing, this shark would not be able to claim all the spaces as its territory.

Anything that is not food or tank décor for your pet shark must not reach the bottom of the tank. Else, there would be trouble within the tank.

If you are a beginner hobbyist and must keep this species of freshwater shark, then get ready to do extra work. In all, do not introduce tank mates for this shark yet. Just keep it alone and get used to it first.

Using enough aquarium décor will create various favorite spots for your pet shark. This will make it less aggressive as it can alternate between spaces.

It is good you also know about the Harlequin rasbora (Trigonostigma heteromorpha). This is just a fish for the aquarium bearing “Harlequin” in its name. It is not among the shark family and very different in appearance from the Harlequin shark (Labeo cyclorhynchus). Of course, this is for knowledge sake as you would never mistake the two in the aquarium pet store.

To Wrap it Up

For shark keepers, the Harlequin shark is a stand out fish species for any home aquarium. Of course, it would get the attention of any hobbyist. But, special caution should be taken when keeping this fish species.

This is while we created this page, to guide you in the adventure of keeping a Harlequin shark (Labeo cyclorhynchus).

Keep to the recommendations herein and you would be glad to own this shark species. Even more, pay attention to the caution and avoid chaos.

If this freshwater pet shark seems too aggressive for you to handle, then, take a look at other Freshwater Sharks suitable for a Home Aquarium.