Halocaridina rubra are more commonly known as Opae Ula Shrimp (lit. – Tiny red shrimp), Volcano shrimp, Hawaiian red shrimp, Supershrimp, and Anchialine shrimp. They are known for being bright, beautiful, and easy to care for.
Opae Ula Shrimp are very hardy and low maintenance pets. They can survive in any sized aquarium. They do not need filters, air pumps or heaters. There is almost no need to feed them. Opae Ula Shrimp can live up to 20 years if cared for properly and breed in brackish water.
These extraordinary shrimp are probably the lowest maintenance pet you can possibly get. As long as you keep them appropriately you can keep them for decades!
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Quick Notes about Opae Ula Shrimp
Previously identified as Caridina brevirostris Stimpson, this species was redescribed as a new genus and species by Holthuis in 1963.
|Name||Opae Ula shrimp|
||Tiny red shrimp, Super shrimp, Hawaiian lava shrimp, Hawaiian red shrimp, Hawaiian volcano shrimp, Anchialine shrimp, Micro lobster, Wonder shrimp|
|Scientific Name||Halocaridina rubra|
|Tank size (optimal)||5 gallons (~20 liters)|
|Size||1.5 cm (0.5 inches)|
|Optimal Temperature||20 – 27°C (~68°F – 80°F)|
|Water type||SG = 1.008 – 1.018 (or 10 to 23 ppt)|
|Optimal PH||8.0 – 8.5|
|Optimal KH||0 – 12|
|Nitrate||Less than 20 ppm|
|Life span||up to 20 years|
|Color Form||Vary in redness and opaqueness|
The Legend of Waianapanapa Caves
Do you know that Opae Ula Shrimp are a part of Hawaiian folklore?
According to the legend, “Once upon a time, a Hawaiian princess named Popoalaea fled from her cruel husband, the chief Kakae. She hid on the ledge just inside the underwater entrance to this cave. A faithful serving maid sat across from her fanning the princess with a feather kahili, a symbol of royalty. Noticing the reflection of the kahili in the water, the chief Kakae discovered Popoalaea’s hiding place and killed her. At certain times of the year, tiny red shrimp appear in the pool, turning the water red. Some say it is a reminder of the blood of the slain princess.”
Origins, Natural Habitat of the Opae Ula Shrimp
Opae Ula Shrimp are indigenous to the Hawaiian Islands and are found in tidal and anchialine pools (pronounced “An-key-ah-lin”, from Greek ankhialos, “near the sea”) there. Anchialine waters are those that are found inland, but are linked below the surface with the ocean and thus are brackish and susceptible to tidal flux.
Anchialine pools have salinity that varies both from pool to pool and from the surface to the depths of the pools (from less than 2 % to 33.5 % or more). This makes Opae Ula Shrimp extremely hardy and capable of withstanding a wide range of salinity levels and temperatures.
These shrimp occupy two physically different habitats, the well – lighted shallow pools and the habitat of dark crevices in the water table below the pools.
Description of the Opae Ula Shrimp
Opae Ula Shrimp are quite small, growing to no larger than half an inch (roughly 1.5 centimeters) in length. Though they may be seen in many colors – clear, yellow, orange, nearly translucent, pale cream and pink, for example – the most numerous and most recognizable form of Opae Ula Shrimp is a vibrant red.
So vibrant in fact, that shrimp can transform the appearance of water and benthic surfaces of an anchialine habitat when large numbers of individuals aggregate together.
When Opae Ula shrimp are disturbed, they turn pale or lose the red color over a part or most of their body. This adjusts after variable periods of minutes or hours to the original intensity of redness.
Molting Opae Ula Shrimp
Unfortunately, nobody has ever documented the process of molting in this species. In addition, because of their tiny size and slow metabolism, there is no data about the frequency of their molt.
Sexing Opae Ula Shrimp
In most Caridean shrimp the structures on the first and second pleopod are the features used to distinguish mature males from females. Because of Opae Ula shrimp small size, determining the sex of the shrimp is done at an almost microscopic level.
There are subtle differences between the structures of male and female pleopods – the limbs that they use for swimming. These can be seen on shed exoskeletons as well as on live shrimp.
However, most aquarists are not scientists and use other ways to sex the shrimp. For example, like some other shrimp, mature females have broader abdomens where they carry the eggs. Males tend to be slimmer and have straighter undersides. Also, the females of Opae Ula shrimp usually have a more vibrant red color than the male. The saddle and clutch of eggs are the easiest way to tell the sex of these shrimp.
The Feeding Behavior of the Opae Ula Shrimp
Opae Ula shrimp exhibit two feeding methods in their natural habitat.
- Scraping (plucking or grasping)
They use both pairs of chelipeds (pereopods I and 2) with the palm down, to the substrate and then lifted up and reapplied in rapid succession.
- Filter feeding
In this method, Opae Ula shrimp hold chelipeds so that the fans of setae are open and directed anteriorly. As the shrimp swims, the fans filter small particles from the water. This is considered to be the typical feeding mode of stream-dwelling shrimp (Vampire shrimp or Bamboo shrimp), but these shrimp remain stationary with the fans oriented into the current.
The first method is the most common. Opae Ula shrimp are primarily grazers. This scraping activity is crucial in maintaining the integrity of the crust, actively growing algae, bacteria, diatoms, protozoans, etc. Filter feeding is only observed in pools with dense phytoplankton blooms.
Feeding Opae Ula Shrimp
The shrimp will primarily eat algae and biofilm that forms in a tank but can be fed blanched vegetables, fish food, and shrimp flakes. Spirulina is also an excellent supplement to Opae Ula Shrimp diet. If the shrimp tank is placed in indirect sunlight the shrimp will need to be fed only every few weeks or even months! As algae and biofilm will naturally form on surfaces within.
Note: Laboratory and field studies have shown that Opae Ula shrimp are also attracted to insects that float at the surface and carrion. Before this, shrimp have been kept in aquaria for periods in excess of 3 years without receiving any additional food!
To supplement their algae diet, you can also feed them for color enhancing shrimp pellets once every week or month.
Tip: Do not feed Opae Ula shrimp for a month or two after you introduce them to the tank. Do not worry, they will feed on algae and bacteria during this time. You need to do that to prevent overfeeding. Remember, if there as algae in the tank then there is enough food for the shrimp.
Overfeeding Opae Ula Shrimp
These shrimp need a very small amount of food. For example, a single tiny pellet (few millimeters) is sufficient for a 5 – 10 gallon tank (~20 – 40 liters) housing hundreds of Opae Ula shrimp.
Even if you go on vacation and do not feed them for a month or more it will not affect them. Always remember that Opae Ula shrimp have an extremely slow metabolism. They simply do not eat that much. In any case, it is much better to underfeed than to overfeed.
Tip: Use feeding dishes and remove any uneaten food the next day to avoid polluting the water.
Keeping and Housing Opae Ula Shrimp
Opae Ula Shrimp are known for being hardy and surviving in a wide range of conditions. They can be found in pools, aquariums, ecospheres, and even mason jars. In order for the shrimp to thrive and breed they should be given the best possible environment.
Opae Ula Shrimp can be kept in containers as small as a half-gallon (~2 liters). However, these are difficult to keep balanced, and, in addition, they will reproduce better if they are in larger containers. Therefore, people who wish to keep Opae Ula Shrimp should plan on housing them in a tank of at least 5-gallons (~20 liters).
Cycle your tank
Opae Ula Shrimp are hardy enough that some people even introduce them before the tank fully cycles. Well, I hope that you are not one of them! Although these shrimp are very resilient, it will be unnecessary stress, which will affect their life cycle anyway.
Most tanks have to cycle for 6 to 8 weeks and sometimes even longer so that the level of ammonia and nitrates that build up from waste don’t kill whatever you have in your aquarium. Do not buy your shrimp until the tank has had a chance to cycle.
Tip: You can add some snails to boost cycling. Read more about it in my articles:
Step-by-Step Cycling your Shrimp Aquarium Fishless.
Benefits of Snails for a Shrimp Aquarium.
Water for Opae Ula Shrimp
The water should be brackish, with a salinity between one and eight thousandths and one and eighteen thousandths specific gravity (1.008-1.018 sg) as measured with a refractometer. An appropriate and simple way to determine the appropriate salinity for the initial tank setup is to ask the breeder for the salinity upon purchase and match it.
Note: In the laboratory, Opae Ula shrimp tolerated salinities of 0 – 50%. They can adapt to lower or higher salinities. However, they do really well at around 50% seawater and they do not breed very well if the salinity is too high or too low.
The pH should be kept around eight (8.0). A source of calcium carbonate, such as aragonite or coral, is essential as well.
Note: Only marine salt should be used to maintain the salinity of the tank. Do not use aquarium salt or table salt or any other salt you can think of just use marine salt.
Distilled water or reverse osmosis water is your choice. RO water is foolproof. It means that you will never have things in it that can wipe out your shrimp colony. The marine salt mix does a fine job of remineralizing.
Tap water contains chemicals like chlorine and chloramine. You do not need that. Of course, you can use Seachem Prime (link to check the price on Amazon) to remove them but why shot yourself in the foot, right?
A filter is not strictly necessary for an Opae Ula shrimp tank. They do not need filtration beyond the natural biological filtration that will occur in the aquarium when it is properly setup.
Temperature and Heater
Opae Ula shrimp originate from the anchialine pools of Hawaii. There they are found primarily near the surface, in the water warmed by the sun. Thus, the temperature of the Opae Ula Shrimp tank should be kept between 68 – 80 °F (20 – 27 °C).
Therefore, they do not need a heater as long as you have reasonable room temperatures (unless the room gets below about 60 F or 15 С).
Opae Ula shrimp do not need any additional aeration. They thrive in low oxygen environments in the wild. In addition, it stresses them.
If ambient light allows algae to grow, it is usually enough for the shrimp. In case you really like an aquarium light, do not choose something too bright. First of all, Opae Ula shrimp do not need too bright light, they live mostly in darkness in lava tubes in Hawaii. Second, it can encourage excess algae growth, and you do not need that either. You will have to find some balance.
You can use any substrate you want in your tank from rocks to gravel to sand. However, ideally, it should provide calcium in the form of calcium carbonate to the shrimp. For example, aragonite sand. There is no need to add a lot, 1.5 – 2.5 cm (0.5 – 1 inch) will be enough.
Tip: Rinse it first. Make sure it is clean.
Tip #2: The black sand also helps to bring out their red color
Opae Ula Shrimp should be provided with coral, limestone, lava rocks, etc. to provide shelter as well as surface area for grazing on algae and microbes.
Tip: Do no use things like live rock from marine tanks. Most of the organisms on that rock cannot survive in low salinity and will die off.
Unfortunately, you cannot keep live plants in Opae Ula shrimp tank. I am sure that you read somewhere else that most low-tech plants do fine in brackish water. For example, Anubias, Java fern, Lava moss, etc. Well, this is not true.
Sure, the plants can stay green for a very long time even in brackish water. In some cases, they even start growing a little. However, eventually, they will all die off. Basically, the green color should not trick you. They are “dead man walking”.
The only plant you can keep in Opae Ula shrimp tank is Chaetomorpha macro algae. It is completely adapted to salinity.
How often do you need to do water changes in Opae Ula shrimp tank? Amazingly unlike most aquatic organisms, this species does not require partial water changes if maintained properly. However, to compensate evaporation, you will need to top off the tank with distilled or RO water.
Important: Do not add salt when you do top off. Salt does not evaporate! So if you keep adding saline water all the time you will increase the salinity every time in the tank.
Number of shrimp
How many shrimp can you keep in your tank? Fortunately, since Opae Ula shrimp do not require a lot of space and do not seem to overpopulate their environment you do not have to worry about where to put all the extra shrimp.
For example, in a 10-gallons (~40 liters) tank you can keep 100 – 200 shrimp with no problem. Basically, you can have 5 – 10 Opae Ula shrimp per 1 gallon (4 liters).
Opae Ula shrimp may be very pale (based on stress) when they arrive and that is pretty normal. Therefore, if they look a little pale when you get them do not worry about it they should darken up later. Do not put them in the tank at once. It will be better to acclimate Opae Ula shrimp first. Read my article “How I Drip Acclimate Shrimp and Why”.
Basic Tank Equipment (links to check the price on Amazon)
Ecospheres For Opae Ula Shrimp
A special note should be made about ecospheres. These are closed system habitats containing Opae Ula shrimp, usually along with a sea fan and often with a bit of algae in a glass enclosure. They are sold as a self-sustaining ecosystem that does not require any maintenance. Well, they are not!
They are not designed to produce enough algae to properly feed the shrimp for their natural lifetime. These novelty items have an average lifespan of 2 – 3 years. The natural lifespan of the Opae Ula Shrimp is 10 – 20 years.
Do not use the ecospheres. It will be a torture chamber for your Opae Ula shrimp. An open system habitat, such as an aquarium, at least allows for adjustment of conditions if there should be any sort of catastrophic system failures, such as a spike in pH.
Mating Opae Ula Shrimp
There are several requirements that must be met before Opae Ula Shrimp will begin breeding. The first cannot be controlled for by the tank owner and that is the sexual maturity of the shrimp. They reach maturity approximately one (1) year after hatching. This could be anywhere from 3 to 8 months after they are added to a tank, as most Opae Ula shrimp are sold while they are juveniles.
An important consideration is keeping the water conditions stable and appropriate for breeding. While Opae Ula Shrimp can survive in a wide range of settings, they will only breed if the water in their tank meets their needs properly.
A pH level between eight and eight point four (8.0 – 8.4) is ideal for breeding. Nitrate, nitrite, and ammonia levels should be at or approaching zero (0). There must be sufficient space for the shrimp – they are unlikely to breed in a half gallon (2 liter jar). The temperature must be warm and stable, between 21-24 °C (70-75 °F). Salinity levels should be kept between 1.010 – 1.013 specific gravity as measured on a refractometer.
When sexually mature female Opae Ula Shrimp molt, they will release pheromones that attract the attention of the male shrimp letting them know that they are available for mating. For this purpose, there need to be dark, hidden places in the tank in which mating can occur.
Breeding Opae Ula Shrimp
I would like to start off by saying that Opae Ula shrimp do not breed very often. So do not expect them to breed like Neocaridina or Caridina shrimp. Opae Ula shrimp are low form breeders and have a very slow metabolism. It takes them a lot of time to become ready. That is why females can produce only a few times per year.
Once fertilized, the female shrimp will carry eggs on her belly in a stage called “berried”. According to the study, adult females of Opae Ula shrimp (12 mm long) carry about 14 – 18 large (1mm) eggs on their abdomens for approximately 27 – 38 days that release larvae over 1 to 5 days.
The larvae will float and develop in the water column in the tank, eating their yolk sacs for about 25 – 30 days, progressing through 4 zoeal stages and 1 mysis stage before metamorphosis and settlement.
Note: You do not need to feed the larvae.
Then they will look and behave more like the adult shrimp during their final larval stage of development, called megalopa, which lasts just over a week. After this point, they will enter their juvenile stage, at which point they are distinguishable from adult shrimp only in size.
Important: Survivorship of Opae Ula shrimp larvae from early developmental stages to metamorphosis as juveniles differed significantly among salinities. For example, according to experiments, 88% and 72% survived and underwent metamorphosis into juveniles at 15% and 32% respectively. While only 12% did so at 2%. At the same time, larvae at 15% were also 2 times more likely to survive to settlement as juveniles than were those at 32%.
Interesting facts about Opae Ula shrimp larvae:
- They are phototaxic (adjust orientation in response to light).
- They can hang almost motionless in a head-down position in the water.
- The adults do not attack larvae. So you do not need to worry about that.
Opae Ula Shrimp Larval Development
Morphology of zoeae, megalopa, and juveniles is described in the studies. Juveniles are readily distinguishable from the adults by their small size and pale coloration. In the post-larval juvenile stage, they begin to move horizontally and diagonally.
Opae Ula Shrimp and Suitable Tankmates
Opae Ula shrimp are not predaceous nor are the chelae utilized in defense. In the wild, this species appears to be successful, where predators are absent.
Opae Ula Shrimp and Fish
Opae Ula shrimp are very small and will become prey for most fish when kept in the same tank. The brackish water further limits the available options. In addition, the presence of potential predators will directly affect their behavior by making them less active during the day (or night).
According to the results of experiments, Opae Ula shrimp hid in the refuges in more than 95% of observations during the day but were abundant in those locations at night. In contrast, in a pool dominated by the nocturnal predator, Opae Ula shrimp density was significantly lower during the night than during the day (i.e., a pattern opposite to that of shrimp in pools containing fish).
As we can see Opae Ula shrimp do not like to be kept with fish.
Opae Ula Shrimp and Snails
There are not many snails that can live in the specialized environment for Opae Ula shrimp. Once again, the main reason is shrimp’s slow metabolisms. Therefore, if you are feeding the snails enough you are feeding shrimp way too much! In addition, snails produce a lot of bio-load. As a result, you will have to add filtration to your tank, which Opae Ula shrimp do not need.
I know that some aquarists manage to keep Malaysian Trumpet Snails with Opae Ula shrimp. When you put them in a brackish water situation and without food, they never get large and barely reproduce. As a result, they will not overcrowd the tank.
Sometimes the Hawaiian endemic pipipi snails (The Black Nerite Snail) become neighbors of the shrimp. The Pipipi snails (which means “small and close together” in Hawaiian) are typically about a centimeter in size and tend to aggregate in large groups just above the water level. Like all Nerite snails, they are great algae eaters so keep it in mind. Make sure they get enough algae to eat.
Opae Ula Shrimp and Hermit Crabs
Hawaii dwarf hermit crabs (Calcinus laevimanus) can safely be kept in a tank with Opae Ula Shrimp. This is one of the smallest Hermit Crabs (less than 1 inch or 2.5 cm) will not harass shrimp. However, it will require more food leading it to overfeeding.
Overall, Opae Ula shrimp will be better in species only tank.
Opae Ula shrimp are the easiest shrimp for the beginner. They are so hardy that you can use almost any glass container with good a light source for algae growth. Once you have a cycled tank, the best thing to do is just leave them alone.
You do not even have to feed them often. These shrimp tend to thrive a lot better if they are not disturbed. They are also cool to watch and don’t hide as much as some shrimp.
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- Reproduction and Development in Halocaridina rubra Holthuis, 1963 (Crustacea: Atyidae) Clarifies Larval Ecology in the Hawaiian Anchialine Ecosystem. Biological Bulletin. 229, No. 2, October 2015. DOI: 10.1086/BBLv229n2p134.
- Feeding, Reproduction, and Sense Organs of the Hawaiian Anchialine Shrimp Halocaridina rubra (Atyidae). Pacific Science (1993), vol. 47, no. 4: 338-355.
- Behavioral Responses of the Endemic Shrimp Halocaridina rubra (Malacostraca: Atyidae) to an Introduced Fish, Gambusia affinis (Actinopterygii: Poeciliidae) and Implications for the Trophic Structure of Hawaiian Anchialine Ponds. Pacific Science (2009), vol. 63, no. 1:27–37.
- Intrusion of Anchialine Species in the Marine Environment: The Appearance of an Endemic Hawaiian Shrimp, Halocaridina rubra, on the South Shore of O’ahu (Hawaiian Islands). Pacific Science. October 1999.
- Islands under islands: The phylogeography and evolution of Halocaridina rubra Holthuis, 1963 (Crustacean: Decapoda: Atyidae) in the Hawaiian archipelago. Oceanogr., 53 (2), 2008, 675–689.
- Osmoregulation in the Hawaiian anchialine shrimp Halocaridina rubra (Crustacea: Atyidae): Expression of ion transporters, mitochondria-]rich cell proliferation and hemolymph osmola. Journal of Experimental Biology. April 2014. DOI: 10.1242/jeb.103051
- Predator-dependent diel migration by Halocaridina rubra shrimp (Malacostraca: Atyidae) in Hawaiian anchialine pools. Aquatic Ecology. March 2011. DOI: 10.1007/s10452-010-9321-0.
- Larval development of Halocaridina rubra Holthuis (Decapoda, Atyidae). Crustaceana 34 (3) 1978, E.J. Brill, Leiden.