Thai Micro Crab: New Breeding Progress

20 Mar, 2014

The Thai Micro Crab, or Spider Crab, is a diminutive crustacean with a carapace size roughly the diameter of a pencil eraser. Plant and shrimp safe, they have been gaining quick popularity in recent years. Despite their relatively frequent availability within the hobby, almost no breeding reports have been published.

Microcrabs (Limnopilos naiyanetri) busy filtering for food.

Microcrabs (Limnopilos naiyanetri) busy filtering for food.

Limnopilos naiyanetri (Chuang & Ng, 1991) are a Hymenosomatid crab found in Southeast Asia. The species is characterised by its flat, pilose (hairy) carapace and chelipeds (legs). A popular and enchanting addition to a small invertebrate tank, they are completely peaceful and tolerant of a wide range of parameters and add an additional level of interest to a small tank.

While a shy and unassuming addition, once the crabs settle into a tank, they can usually be found clinging to decor or on the roots of plants, as shown in the video below.

While it has long been said that they complete their life cycle in freshwater, there have not been documented breeding reports with photographs to support suggested success. There is much anecdotal evidence available on the internet, and many reports of the female holding eggs, which change from orange to tan to grey, under her pleon until they hatch into larvae and are released. Some anecdotal breeding information suggests that the larvae may need an orienting light. Many people, myself included, have been working with various strategies to rear them with little success.

In the past, I have seen females release larvae many times, and have seen rare instances of baby crabs in the tank, but have not had any success with any consistent rearing of young. I have had a female holding eggs for several weeks. Without my notice, they hatched into larvae and she continued to hold them. It appears that they have transitioned into young crabs, a very exciting discovery! This suggests that the larval release may be premature, and would explain a lot of my previous failures.

Female microcrab seemingly holding young crabs.

Female microcrab seemingly holding young crabs.

I have them set up in a tank with leaf litter, driftwood, and some low light plants including red root floater, anubias and some bolbitis fern. They spend most of their time in the dense roots of the plants, or the crevices of the wood. They appear to use their pilose (hairs) to detect food, largely eating particulate foods (I use Golden Pearls, and Nano Bites, as well as occasional frozen cyclops).

The tank temperature is around 74F, with a pH of 7.4, gh 7, kh 8, tds around 180. Water changes are done twice a week, consisting of a 25% exchange. Hopefully the baby crabs will be released soon and I will have further success in order to have a better idea of what exactly was the difference with this setup over previous attempts.

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About the author

Rachel O'Leary
Rachel O'Leary

Rachel O'Leary is the owner and operator of msjinkzd.com, a business specializing in freshwater nano fish and dwarf invertebrates. She is a published contributor to such magazines as Amazonas, as well as a renowned national and international speaker. Rachel is a frequent, and colorful, presence at many clubs and conventions in the United States and Canada.

23 Comments

  1. March 30, 2014

    What are the water parameters that you keep them in?

  2. April 02, 2014

    They are kept in my well water, which has a pH of about 7.4, gh 6, kh 7, tds which varies from 150-180. Their tank is unheated, at about 72 degrees this time of year.

    • September 29, 2015

      Have you figured out exactly what got the crabs to survive past the zoa stage?

  3. July 23, 2015

    Where the young successfully raised to adulthood?

  4. July 26, 2015

    I’m looking foward to doing nano aquarium sized animal breeding soon. Sadly I’ll probably not be able to start for a year, but while reading alot about thai micro crabs, I think I know something fail safe for breeding, I can’t wait to try it out, would you be willing to donate some adults?

  5. January 20, 2016

    So I purchased one and poor it in a separate breeder tank with my daughters guppies. A couple of days later my tank was filled with babies. At first I thought it was an infestation of some sort. It had been almost a month and they appear to have grown a tiny bit. I don’t know how I have kept them alive this long but they are still doing great. The guppies don’t bother them and they don’t bother the fish.

  6. March 16, 2016

    Linda are the babies growing or did they die?

  7. February 15, 2017

    Hi, have you ever noticed a behaviour in them where they ‘install’ rotten plant materials on themselves, at the top of their carapace? I just got one and observed this interesting behaviour but could not find any other information on that.

  8. guy
    March 04, 2017

    are they violent as i am interested in buying one but if it will attack/harm my asian stone catfish i’ll just forget it

  9. May 04, 2017

    Thank you for sharing. Very nice.

  10. May 31, 2017

    Has anyone tried removing the parents and raising the salinity?

  11. June 13, 2017

    It would seem to me almost obvious if water quality was such they were breeding, carrying eggs full term, and birthing successfully but then the young die we are talking about the young needing a certain dietary food source not available in most tank environments. These crab come from one river in Thailand and nowhere else so it’s not a salinity thing or water issue as the water would remain somewhat constant in a river system although does any know what the parameters are in this river. It has to be a micro algae or maybe algae in general that most aquarium environments lack. I just picked a few up for my shrimp tanks wish me luck..

    • January 12, 2018

      smartest reply ive seen.
      Why not just replicate what goes on in nature. well within our ability ( we got to the moon ). Would be VERY interested to know what the parameters are in the thai river and also what kind of vegetation including (well pointed out) micro algae/basic algae.

      • February 15, 2018

        Well, I just got myself 20 of the little creatures. I’ve been searching my rear end off, to find out the name of the river in Thailand, where they come from. I guess it’s not documented anywhere, to prevent people from taking out too many of them, illegally. So: no success in finding out the name of the river yet, and consequently no way to determine the paramters of the crabs’ natural environment.
        However, even though we are talking about Thailand, I feel it hard to believe that the minimum temperature of a river / stream (flowing water) there is acutally 22 degrees Celsius, as suggested by just about everybody selling them.
        If I look at my self-made water-stream in the back yard, and take the water temperature at minimum 22 degrees Celsius air temperature at night (in summer), the water temperature is significantly lower (at least 3 – 4 degrees Celsius). I live by the Rhine river in Germany, so I don’t even want to mention the water temperature in that river, with the mentioned air temperature.
        So perhaps, it’s also a temperature issue, where the temperature for a certain period of time must fall below a certain limit, in order to get the right breeding result, besides the natural dietary food, which must be important too.
        At any rate, I will find out about the crabs’ reaction to slightly lower temperatures, their possibilities to adjust, and perhaps the breeding, in due time – and maybe come back with my experience…

        • February 15, 2018

          Sorry!
          Forgot to mention that the outside air temperatures in Thailand (on average) go down to:
          – Bangkok = minimum approx. 20° C in December
          – Phuket = minimum approx. 22° C in January
          – Koh Samui, Koh Phangan, Koh Tao (= South-Eastern Islands) = minimum approx. 22° C in January
          – Chaing Mai (the North) = minimum approx. 14° C in January
          So even if the sea temperature for swimming tends to be warmer, the temperature of a river / stream / flowing water has a tendency to be lower.
          Just thought I’d add that to my previous ideas.
          And Yes, I also think that James’ reply was the smartest I’ve seen, matching my own thoughts too.

          • February 17, 2018

            The beauties explore all corners of their new home, a 30 Liter Dennerle Nano Cube, at room temperature, which means approx. 18° C water temperature right now. Very active, some decided to move into the 25 x 15 cm Mopani root with many “caves”, others dwell on/around/underneath Moss-balls, again others seem to enjoy Zeolith rocks, a few hang out in the plants – altogether an enjoyable bunch to search for and watch thereafter. The European Freshwater Shrimp “Atyaephyra Desmaresti”, the Heterandria Formosa, the local Gammarus and the Ramshorn Snails pay them a visit occasionally, but without any harm, all very peaceful. I love it!!! 🙂
            Will report more later.

  12. Jon
    August 19, 2018

    As a scientist and someone who is interested in breeding microcrabs in the near future, I have looked into some old papers to try and determine the location which the Thai micro crabs are originating. My purpose in doing so is to provide further information to the community on the ecology and habitat in which the Thai micro crab lives in order to facilitate successful breeding within the hobby. While I have done the scrounging and cross referencing, the information provided here is not mine, but is largely due to the work of Dr. Peter K. L. NG from the National University of Singapore. I have provide links to all papers which were used in the process of my analysis.
    Please note: there seems to still an update to the genus of the species in the following papers. Older papers will refer to them as Hymenosomatidae; whereas, more recent papers refer to them as Limnopilos. All of these papers are by the same primary author, Dr. Ng. I’m a molecular biologist/neuroscientist and could care less what it gets called, especially when based on physical characteristics. :p From this point forward the species may be referred to as falling in either the Limnopilos or Hymenosomatidae genera.
    Another important note: The journal through which some of these papers are linked will only allow you to open a limited number of their articles per day. Once open, download the article and keep the page open until you are sure it downloaded properly.
    https://lkcnhm.nus.edu.sg/app/uploads/2017/06/39rbz363-368.pdf (Chuang &Ng, 1991 paper). Detailed morphological data but nothing about development, offspring, or region of collection.
    (https://australianmuseum.net.au/uploads/journals/17555/199_complete.pdf) This paper mentions how to discern hymenosomatidae (genus that naiyanetri was originally classified as) larvae from plankton, suggesting that they exist within the same column, rather than on the riverbed. I have made the assumption that colocalization would result in predation (this is not necessarily true).
    Possible foods to try are: Rotifers, diatoms, copepods.
    Locations of collection:
    After much difficulty, I have finally found the location of the Thai micro crab Limnopilos naiyanetri, in addition to information on two other species within the same genera, Limnopilos sumatranus (http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.652.7163&rep=rep1&type=pdf) and Limnopilos microrhynchus ().
    Limnopilos naiyanetri is listed in the afore mentioned paper as being collected in the Tha Chin River, Nakhon Chai Si District, of the Nakhon Pathom Province, in Thailand. No coordinates are given.
    A large number of changes can occur during speciation, or very few; it’s all a role of the dice. Using Limnopilos sumatranus and Limnopilos microrhynchus as a guide is admittedly flawed, but may provide further insight into the ecology of the genera. This additional information may result in comparative analysis of the river systems and determination of common factors that may lead to determination of proper food, water conditions, and successful rearing of larvae.
    Ng notes that Limnopilos sumatranus was collected when gathering floating vegetation in the center of a stream. The water was acidic (ph not provided) and was colored (presumably by tannin). Specimens were collected on June 5th 1996 at 1°15´9.3″ S, 104°6´49.6″ E (https://www.google.com/maps/place/1%C2%B015'09.3%22S+104%C2%B006'49.6%22E/@-1.2633265,104.1105747,15.5z/data=!4m5!3m4!1s0x0:0x0!8m2!3d-1.2525833!4d104.1137778) When following this link, please note that it is slightly off. The paper states that it was at the junction into the black water reserve.
    Limnopilos microrhynchus specimens were collected at 0°42´ S, 117°38´ E (https://www.google.com/maps/place/0%C2%B042'00.0%22S+117%C2%B038'00.0%22E/@-0.8079812,117.5533196,11.75z/data=!4m5!3m4!1s0x0:0x0!8m2!3d-0.7!4d117.6333333). Again, these coordinates seem to be off. Description of the site states: Bengalon River, East Kalimantan, Indonesia.
    This was my primary source of literature: http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.652.7163&rep=rep1&type=pdf
    I hope to start a micro crab tank in the near future and will begin to experiment with conditions and food sources as soon as possible. This may take a few months. In the meantime, please let me know if any of you manage success or if any of this information has been helpful.
    Cheers,
    Jon
    nelsjm17@wfu.edu

  13. January 24, 2019

    any update?

  14. February 14, 2019

    Very interested in this post! Have been thinking of adding some myself.

  15. August 18, 2019

    I currently have 13 Thai Micro Crabs, and after watching behavior that seemed like possible breeding I began to look into it. I quickly found most people attempt breeding them like neocaridina shrimp. Like you guys im sitting here wondering, why dont you just set up the same environment from which they came? Clearly you guys beat me to that though. If it helps, In search of their habitat I got in touch with a few people in Thailand and they said they believed Thai Micro Crabs were caught in the Chao Phraya river? Also from dntaqua : “It is important to use a tank illumination during breeding attempts, as the zoea are dependent on light to orientate themselves correctly in the water column.” Might help, i kept my tanks light low thinking the hiding space would help, maybe lighting should be high though? ALSO multiple forums now ive seen people saying theyve seen their micro crabs preying on small shrimp fry? Most inverts do very poorly when fed things like shrimp, maybe its the opposite for them and theres a nutrient in shrimp that the baby crabs need??? Also according to an article on mdpi, these “pill-box crabs” definitely spawn in full freshwater, not brackish. Also, alot of sources say theyre mainly found in roots of hyacinth plants, does anyone know if those plants have a specific property thatd attract these crabs? Maybe ill set up an enclosure like that. SUPRISINGLY, i had a hunch that if they are really from the chao phraya river, theyd be used to heavy water flow. I turn up my filters flow all the way throughout the day, and they stay active and even will come up to the filter “with padding on it” and rest and eat off it. They handle the currents extremely well. Maybe they lay eggs and send their offspring down stream to diff conditions? Im trying to think outside the box here… though they genuinely do seem to be more active during the higher flow (probably because more particle movement in the water for food.) ALSO IT IS JUST ASSUMED THAT THESE CRABS LARVAE DEVELOP IN WATER!!! It is not recorded yet, just assumed, for all we know they may bury in substrate or even be layed on land to return to water. It hasnt been documented yet. Im going to try to make a land area in the tank for them with moist substrate, just incase. I currently have 13 thai micros which i got for an unbeatable $19.99 , im waiting for more to come in stock so i can double or triple down on that in hopes of breeding them. In the meantime im going to try to contact some people from the areas these are present, and see what they can tell me about their habitats. U/satansearthworm on reddit posted footage of his crab spawning underwater, and the eggs seemed to float off drifting away, this lead me to believe in the wild, the eggs float down stream and many most likely end up on the riverbank or stuck on floating plants right? The videos here: https://www.google.com/amp/s/amp.reddit.com/r/Aquariums/comments/aqx3iv/caught_a_rare_sight_my_thai_micro_crab_spawning/ also on the same thread: “The biology is not well known. I have kept them in wholly freshwater with water weed and they have bred. Try using slightly harder water – maybe pH7 or 7.5 …. you should keep them in large groups as they seem to do poorly in small groups.” Right now my ph and kh are a bit high, ill try to keep it that way, my shrimp seems to really thrive in high kh. A video from Rachel O’Leary says that she believes the female crab carries the eggs until after hatching, where she continues carrying the babies for weeks, however the footage from the reddit clip is contrary to that. Were all keeping our tanks in the mid to high 70s but why? I find it somewhat hard to believe that river stays so warm. Also WHY do the crabs change color from brown to clear?? Is it indicitive of anything? Ive never seen my micro crabs molt, and ive heard it happens when they change aquariums, but do we know for sure? Does it have to do with sterility? The reddit threads crab was pretty dark red/brown, NOT clear, so maybe only a few, like the darker colors are capable of spawning? Also, apparently the mother crab was spawning the eggs in the dark, then the redditor turned on the lights and the crab released the eggs in the water, they suggest it may be a defense mech. Maybe try keeping them in the dark, with little noise so that the mother crab keeps the babies held onto? Anyways thats all i got for now, hopefully i can get my hands on even more of them to increase chances of breeding. Please guys lets try to find out more about their natural habitats. If you guys have any useful info on breeding them email me please!

  16. August 28, 2019

    Have you checked your salt content in the water? Usually all freshwater has about 0.5 ppt or lower so there’s a chance the level of salt present my determine premature release and holding the larva

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