The Harlequin shrimp (Hymenocera Picta) is becoming a much more common sight in domestic aquariums. These wonderful little invertebrates are interesting to watch and are relatively low maintenance to care for.
The Harlequin shrimps are the most striking crustaceans in the world, showing unique coloration and morphological features. They can also serve as diligent little security guards, keeping your corals safe from parasites (like Asterina starfish) by hunting and eating them, before the pests have the chance to do any harm. By taking care of your Harlequin shrimp, they will return the favor by keeping your aquarium safe and healthy.
The colorful Harlequin shrimp is an extremely valuable marine ornamental species. Unfortunately, the feeding habit of this species also possesses a problem for hobbyists wishing to display it in reef aquariums.
Quick Notes about Harlequin Shrimp
| Name | Harlequin Shrimp |
| Other Names |
Harlequin Shrimp, Painted Shrimp, Clown shrimp |
| Scientific Name | Hymenocera Picta |
| Tank size (minimal) | 10 gallons (~40 liters) |
| Keeping | Easy-Medium |
| Breeding | Difficult |
| Size | 4 – 5 cm (~1.5 – 2 inches) |
| Optimal Temperature | 28 – 32°C (~82°F – 89°F) |
| Water type | SG = 1.023 – 1.025 |
| Optimal PH | 8.0 – 8.4 (7.5 – 9) |
| Optimal KH | 8 – 12 |
| Nitrate | Less than 20 ppm |
| Diet | Carnivorous (eats only starfishes) |
| Temperament | Aggressive (Territorial) |
| Life span | up to 7 years |
| Color Form | Large colorful spots (red or blue blotches in the body) |
Natural Habitat of the Harlequin Shrimp
In the wild, Harlequin shrimp are typically found in the Indo-Pacific and Central Pacific regions Ocean. However, there are also several reports of this species in the eastern Pacific region as well.
Note: Literature records indicate that Hymenocera Picta inhabits the oceanic islands of Galapagos, Gorgona, Malpelo, Perlas, Clipperton, and in the coastal zone of Costa Rica.
Harlequin shrimp are usually observed between 1 – 30 m depth. They usually live in pairs and associated with holes, crevices, and caves in coral reefs.
Description and Behavior of the Harlequin Shrimp
Harlequin shrimp are not only kept simply to keep pests away, but marine enthusiasts also keep them for their natural and unique beauty, which is making them a rather fashionable addition to many people’s aquariums.
Hymenocera picta is commonly known as “Harlequin Shrimp” or “Painted Shrimp”. The shrimp are usually white with large colorful spots (red or blue blotches in the body) adorning their bodies, almost giving them a fluorescent look. Harlequin shrimps are shaped slightly like a praying mantis with leaf-like appendages.
This is a relatively small shrimp. A fully-grown Harlequin shrimp can reach up to ~5 cm (2 inches) in size, which can really make them stand out in smaller aquariums.
Hymenocera picta species can live up to 7 years, so your fish and other animals in the aquarium will hopefully have a companion for plenty of time.
This species is monogamous and territorial. Combat is something the Harlequin shrimp are capable off when underwater.
Sexing Harlequin Shrimp
1. In Harlequin shrimp, females are generally larger than males.
2. Females also exhibit larger colored blotches in the ventral region of their abdominal segments (they have blue/purple spots under the tail). Adult males lack the blue tips of the pleopods, present in adult females, and have the second color patch on the side of the abdomen only weakly developed.
3. Harlequin males develop an appendix masculina and an appendix interna, while females develop only an appendix interna.
Note: Unfortunately, you will need a microscope for that. Therefore, it is just easier to look under the tail.
Asterina Starfish and Harlequin shrimp
To make the long story short, Harlequin shrimp eat Asterina starfish. These creatures are not like regular starfish. They are smaller and can act as an infestation that can negatively affect other marine wildlife.
Note: There are many species of Asterina starfish. Some of them are coral safe. While others can destroy your reef tank. The problem is that it is very difficult to tell which species of Asterina you have. Another problem is that they multiply like rabbits. Therefore, if you see only one Asterina starfish there are probably many others hiding somewhere.
Harlequin shrimp help reduce these infestations by feeding on them, having a beneficial impact on the corals. Harlequin shrimp are very adept hunters and their hunting behavior is fascinating to watch to marine enthusiasts.
Diet of the Harlequin Shrimp
Many people add Harlequin shrimp to tanks to keep the pest (Asterina starfish) population down. However, in time they may eat them all and run out of food. So what else can you give your shrimp?
The answer is that Harlequin shrimp feed exclusively on starfish. We all know that in general, shrimp feed on a variety of food and do not display selective feeding regimes, because they are scavengers. However, Hymenocera picta species has a special feeding behavior, which, feeds only on starfishes.
I have mentioned this problem at the beginning of the article. As an owner, you will have to buy starfish from a pet store in order to keep your shrimps well fed.
Do not worry about the size of the starfish. Harlequin shrimp is a predator, hunting for large prey. For example, a mature pair of shrimp can eat two to three specimens of starfish (6 – 10 cm or 2.4 – 4 inches in diameter) each week.
Pair of Harlequin shrimp is pretty good at cooperation. They can help each other to turns the starfish upside-down and then pierce its skin with the first pair of legs, which possess sharp and tiny claws.
Note: According to observations, both the sexes are equally effective in hunting. However, males are more agile and find new prey faster. But females feed more on prey because of the larger size and their need to increase their reproductive value.
In the laboratory, the Harlequin shrimp took every kind of starfish offered.
| Types (Families) of Starfish for Harlequin shrimp (Food Menu) | |
| Acanthaster | Leiaster |
| Astropecten | Mithrodia |
| Asteropsis | Nardoa |
| Archaster | Nidorellia |
| Asterina | Oreaster |
| Ceramaster, | Oreasteridae |
| Culcita | Pentaceraster |
| Fromia | Protoreaster |
| Linckia | Phataria |
| Holothuria | Etc. |
Basically, Hymenocera Picta will eat almost any starfish you give them. The harlequin might eat the Serpent (Brittle) star as well if it gets hungry.
Interesting fact: Biologists noticed that Harlequin shrimp responded rapidly to fast-moving specimens. However, their response and time to initiate feeding on the comparatively slower-moving species of starfish were much slower.
If starfish were almost “static” specimens (for example, Culcita novaeguineae) they did not even attempt to hunt it down!
Molting of the Harlequin Shrimp
One important aspect of Harlequin shrimp care is being aware of their molting habits. This is when the shrimp shed their shell (exoskeleton) as they grow. “Old” shell prevents their growth and development because their exoskeletons are rigid. Meaning, eventually it will need replacing.
Sometimes these exoskeletons can look like your shrimp is lying dead and motionless. If you see this, don’t panic, it may just be the discarded shell. It will be worth checking the shrimp’s favorite hiding spots to see if they are in there, recovering from the shedding. However, DO NOT disturb them at that time. Like all shrimp, after molting, Harlequin shrimp are soft and extremely vulnerable.
Both sexes usually molt every 18 – 20 days. Fully-grown Harlequin shrimp can molt every 20 – 30 days.
Note: Naturally, the discarded shell will be much more transparent and lighter than the shrimp themselves, so careful inspection will reveal this.
Harlequin shrimp need adequate calcium supplement and trace minerals in the molting process. I highly recommend reading my article “How to Supplement Shrimp and Snails with Calcium”.
Keeping Harlequin Shrimp
There are other environmental factors to consider when bringing a Harlequin shrimp home such as the temperature of the water. Ideally, it needs to be set between 28 – 32 C (82 and 89 F). In most guides about Harlequin shrimp, you will see that it is possible to keep them at lower temperatures like 22C (72F). Of course, you can but they will not breed. Meaning that this is not their optimal temperature.
The specific gravity required is 1.023 – 1.025. The optimal pH for the Harlequin shrimp is between 8.0 and 8.4. The carbonate hardness has to be from 8 to 12.
In addition to the filter and water pump, you will have to take into consideration that dead or rotting starfish will pollute your water very quickly. Therefore, a Protein skimmer (link to check the price on Amazon) is a very important piece of equipment as well.
Like all shrimp, Harlequin shrimp do not tolerate large ammonia and nitrate level. Be very careful with copper.
It’s important to also be aware that the shrimp are sensitive to water chemistry and any sudden changes can have a negative impact on them so, if mild changes are made it’s safer to do it slowly, giving the shrimp time to adjust.
Also don’t move a Harlequin shrimp into a tank that has a strong current. Some types of fish need this so that means they are not the best tank mates for a shrimp. Only move a shrimp into an aquarium that has a mild current. The shrimp needs to be able to move around the tank comfortably for their own safety, so don’t move shrimp into a tank that has a very powerful filtration system.
Note: You need to acclimate any shrimp before putting them in the tank.
You can read my article “How Copper Affects Dwarf Shrimp”.
You can read my article “Nitrates in Shrimp Tank. How to Lower them”.
Basic Tank Equipment (links to check the price on Amazon)
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Harlequin Shrimp and Hiding Places
Once a solo shrimp is inserted into an aquarium, they will try and locate a home for themselves. This is usually somewhere covered and remote. Harlequin shrimps are often drawn to cave-dwelling, so marine ornaments like toy skulls or sunken pirate ships make an ideal lair. Somewhere the shrimp can retreat if it feels threatened in any way.
The creatures will search out such a location as soon as they arrive and will venture out and explore their surroundings once they become more comfortable and acclimatized to their new home. This can actually be a joy to watch, especially if your shrimp have been particularly shy. Seeing them go exploring can be a satisfying thing to see.
Mating Harlequin Shrimp
Harlequin shrimp have a clear preference for their individual mate with whom they stay most of the time. Once they do so, they usually do not straying too far from their mate. As romantic as humans may find this shrimp pairing, it is really more of nature’s way of keeping both shrimp safe to reproduce faster. Harlequin shrimp are more likely to mate successfully if they stay close to each other, increasing their chances of producing offspring.
Paring is very important. Biologists observed that single females attained puberty at a significantly greater age and larger size than did females paired with males.
The problem is that in with wild, they have a low population density, which was confirmed by field data. That is why, in Harlequin shrimp, partner-fidelity is not sexual fidelity. Males will try to copulate with every available freshly molted female. This is another nature’s way to sustain and increase the colony. It ensures fertilization of the paired female every time she molts. In some cases, it would also allow fertilization of lone females, which happen to be near the pair.
Nonetheless, after mating with another female, the male Harlequin shrimp immediately returns to his preferred female.
Breeding Harlequin Shrimp
Females of Harlequin shrimp become mature only at 200 – 240 days old. Once matured, they spawn after each molt (every 18–26 days). Two hours after fertilization, they transfer the eggs to their abdomens. In general, they are ready to spawn 1000 eggs. However, according to different observations, the number of eggs can range from 100 – 5000. In most cases, it depends on the size of the female, feeding regime, and temperature.
Important: Temperature plays a huge role here. Harlequin shrimp stop spawning when the water temperature drops below 25 C.
Once the eggs begin to turn transparent, it means that they are about to hatch. It is quite an interesting fact but, in the experiments, the female typically stops eating the day before the larvae hatch. Harlequin shrimp larvae hatch out of the eggs within 12 – 18 days. After that, larvae pass through 12 planktonic zoeal stages and reach the settlement stage in 5–6 weeks.
Feeding Harlequin Shrimp Larvae
For the first two weeks, to keep Harlequin shrimp larvae alive you will have to provide a mixed diet of:
- The rotifer (Brachionus rotundiformis).
- Mixed microalgae (Tetraselmis gracilis, Chaetoceros calcitrans, Isochrysis galbana)
- Artemia salina nauplii (Brine shrimp eggs – check the price on Amazon).
After that, you can feed them only Artemia nauplii until they become 40 days old post-hatch. Post-larvae begin eating starfish five days after metamorphosis.
In truth, Harlequin shrimp enjoy living as a breeding pair. So, if you have space and the inclination to let them, the shrimp will be happier for it. This can cost more money in terms of food but you may be able to breed and sell the spawn to other enthusiasts or pet/aquarium stores. Just be aware of the commitment you are taking on, as it’s pretty hard to breed them.
Harlequin Shrimp and Tankmates
Speaking of tank mates, it is essential to know which sea creatures make ideal neighbors for Harlequin shrimp.
They usually cannot live with other Harlequins. Both males and females are aggressive towards individuals of the same sex. There are also reports that males can readily fight each other to death in an encounter.
However, I would not recommend mixing them with other breeds of shrimp as well. Once the shrimp moves into his/her tank they will consider it Harlequin territory and will not want to share this with any other breeds. Fights can and will happen.
Harlequin shrimp can live alongside small fish (for example, Panda goby) in harmony.
Do not include them in an aquarium with much larger or potentially aggressive fish (like Wrasse, Puffers, Damsels, Larger Hawkfish, Lionfish, etc). Even if fish do not tend to attack Harlequin shrimp, the shrimp may feel intimidated by much larger creatures. This can be detrimental to their long-term health. Either causing them to hide away and starve or just generally living in a stressful environment.
Some aquarists manage to keep Harlequins with crabs. Personally, I do not thank that it will be a good idea (for example with Grapsus grapsus (The Sally Lightfoot crab), Stenorhynchus seticornis (Arrow crabs), etc.). Crabs are opportunistic eaters. They will eat whatever they can catch. Therefore, I would not risk keeping Harlequin shrimp with them.