Harlequin Shrimp

English name: Harlequin Shrimp
Scientific name: Caridina spongicola
Origin: Indonesia
Size: 0.25 to 0.5 in
Water temperature: 78 - 85 °F / 25.5-29 °C
Recommended pH range: 7.0 - 8.5
Behaviour: non-aggressive
Difficulty: hard
Breeding rate: low

Introduction to Harlequin Shrimp

The Harlequin shrimp hails from Sulawesi in Indonesia. It is called Caridina spongicola since it lives on sponges.     

Geographical origin and habitat

The Harlequin shrimp lives the island Sulawesi in Indonesia. The hobby is currently supplied with Harlequin shrimp from several different lakes on this island. In the wild, the Harlequin shrimp lives on freshwater sponges and keeps them clean by eating algae and other particles found on the surface. In captivity, it is not obligatory to give your Harlequin shrimp sponges but they will of course be appreciated.

Physical appearance

The Harlequin shrimp is the smallest of the recently discovered shrimps from Sulawesi and has a distinct harlequin coloration and pattern. When introduced to a new aquarium, the Harlequin shrimp will often lose its true colouration and become paler. As soon as it feels safe in its new home the colours will start coming back. The only thing you can do is decorate the aquarium in a way that makes the shrimp feel secure and at home and then wait for it to recover.

Keeping Harlequin Shrimp

Try to resemble the lakes of Sulawesi in your aquarium since this is what the Harlequin shrimp is used to. The water should be hard and the pH-value should preferably be alkaline even though this shrimp usually adapts to neutral conditions as well (the recommended pH-range is 7.0-8.5). Do not let the temperature sink below 78 °F / 25.5 °C. Since this shrimp is used to fairly warm water, it is best to stick to the upper part of the recommended temperature range.

It is very important to keep the levels of nitrogenous waste down. If you encounter a sudden spike, it is okay to let the shrimps be without food for a few days while you figure out the problem.  

When newly introduced to a new aquarium, the Harlequin shrimp is normally very shy. It is important to decorate the aquarium in a way that offers many suitable hiding spots. This shrimp is for instance known to appreciate plants under which it can seek cover. Eventually, the shrimp will realise that the aquarium is a safe place without any dangerous predators and start spending more time out in the open.

In the wild, Harlequin shrimps always lives on sponges but sponges are not mandatory in captivity – they can survive without them.

Feeding Harlequin Shrimp

As mentioned above, the Harlequin shrimp lives on sponges where it east algae and other particles found in the surface of the sponge. In captivity, it can adapt to eating from other surfaces than sponges.

Keep your Harlequin shrimp on varied diet to ensure optimal health. Use algae and algae based foods as a base and supplement with occasional meaty treats. Don’t forget the diminutive size of this shrimp when you chose food for it.

Ideally feed your Harlequin shrimp when the aquarium is dark. Do not feed it more than what it can devour in 2-3 hours.     

Sexing and breeding Harlequin Shrimp

We still do not know if it is possible to sex Harlequin shrimp based on any exterior signs. Males and females have the same colouration. The females might possibly grow somewhat larger than the males (it is common among shrimps) but it is hard to tell in a shrimp this tiny. 

The Harlequin shrimp is known to reproduce in aquaria. The best advice for the prospective breeder is to keep your shrimps in ideal conditions (see recommendations above) and feed them a suitable diet.

Each batch typically contains 10-15 eggs and you can expect them to hatch after 20-30 days.  
The female Harlequin shrimp will carry the fertilized eggs until they hatch. The emerging shrimp look like tiny copies of their parents; they even show the characteristic Harlequin colouration (albeit not as intense).