Pom Pom Crab Propagation

davidflagg

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Anyone know why pom pom crabs are so notoriously difficult to rear? Google shows a couple of dedicated reefers who have tried with all kinds of complicated equipment. Apparently breeding them is about as easy as it is for any invert, but once the young hatch, it suddenly gets too difficult to manage. Apparently they eat a lot. But it seems like the problem isn't in just providing food.
 

ISpeakForTheSeas

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once the young hatch, it suddenly gets too difficult to manage. Apparently they eat a lot. But it seems like the problem isn't in just providing food.
I'd guess it's probably a matter of providing enough of the right food at the right time(s) and figuring out their settlement cues. This is just a guess though.

For the food: some species in their larval stage will eat provided feeders even if they're not (adequately) nutritious for them; so they'll eat but still starve. So challenge one is figuring out a proper first feed. Then, some species also go through periods where that nutritious first feeder is no longer nutritious in the way they need it to be - so they may need to switch to a different feeder that meets their current nutrition needs at a certain time in the species' development, or the species will starve (even if they're eating that first feeder still). Some species go through multiple of these bottleneck periods.

I've heard that either ciliates or copepods would be necessary feeders for these, and that makes sense to me, as if BBS and Rots worked, they'd probably have been reared by now. So, personally, I would assume copepods would be needed, and probably not the easier, more common ones; if you're going to try raising these, I'd probably suggest starting with Parvocalanus crassirostris nauplii and seeing how it goes from there. If they accept the Parvocalanus pods, then I'd expect to need to move up in food size every few days.

For the settlement cues: Some inverts are highly selective about where/when they'll settle and why - if they cues aren't just right, they'll die out. I don't know if Pom Pom Crabs are picky with it, but they may be.
With regards to the substrate settlement:
- Some species need sand, rock, dark areas, specific colors, or other oddly specific things to settle on/in (from what I've seen, inverts are usually a lot more picky with this), so it may help to have a ledge or cave (PVC should be fine for this, if it's even needed, which I honestly kind of doubt) and a little sand in the larval rearing tank.
The above are just some examples of what may be needed; they could also need certain chemical cues, certain available feeds, the anemones they have a symbiotic relationship with, etc., etc.


All of that said, there are still a number of other, less understood factors at play in breeding (such as lighting) that sometimes throw a curveball in breeding plans, so they could be difficult for quite a few different reasons as well. The feeding and settlement just seem like more likely issues to me at this point.
 
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davidflagg

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I'd guess it's probably a matter of providing enough of the right food at the right time(s) and figuring out their settlement cues. This is just a guess though.

For the food: some species in their larval stage will eat provided feeders even if they're not (adequately) nutritious for them; so they'll eat but still starve. So challenge one is figuring out a proper first feed. Then, some species also go through periods where that nutritious first feeder is no longer nutritious in the way they need it to be - so they may need to switch to a different feeder that meets their current nutrition needs at a certain time in the species' development, or the species will starve (even if they're eating that first feeder still). Some species go through multiple of these bottleneck periods.

I've heard that either ciliates or copepods would be necessary feeders for these, and that makes sense to me, as if BBS and Rots worked, they'd probably have been reared by now. So, personally, I would assume copepods would be needed, and probably not the easier, more common ones; if you're going to try raising these, I'd probably suggest starting with Parvocalanus crassirostris nauplii and seeing how it goes from there. If they accept the Parvocalanus pods, then I'd expect to need to move up in food size every few days.

For the settlement cues: Some inverts are highly selective about where/when they'll settle and why - if they cues aren't just right, they'll die out. I don't know if Pom Pom Crabs are picky with it, but they may be.

The above are just some examples of what may be needed; they could also need certain chemical cues, certain available feeds, the anemones they have a symbiotic relationship with, etc., etc.


All of that said, there are still a number of other, less understood factors at play in breeding (such as lighting) that sometimes throw a curveball in breeding plans, so they could be difficult for quite a few different reasons as well. The feeding and settlement just seem like more likely issues to me at this point.
Wasn't expecting something this helpful. I've read and reread the points you made and afterward I tried to research some of these things out, but there just isn't a lot of resources out there yet (as far as I can tell). I have to ask how you know so much about this? Have you talked around with breeders?

If you don't mind me prying with more questions...

What little I've learned from research is that crabs in particular are extremely hard to rear from their larval stage because no one knows what makes them tick - apparently all of it is dictated by hormonal triggers, which are probably hugely affected by environment factors. What you said sounds like the larvae might switch from one kind of plankton to another as they grow, and if any of these are in short supply at the time of feeding, crash. Stuffing the tank with a trail mix of plankton species sounds like a good idea, but quantity might not be enough. What makes you think Parvocalanus crassirostris is a good starting choice? Is there some kind of understanding of which nutrients crab larvae require to grow? That could be a good way to choose which species to use.

All the rearing tanks I've seen for inverts are bare bottom. Is this a requirement, or do you think they can settle on substrate?

Rearing these larvae can't be this difficult, the requirements are probably simpler than we think, it's just a matter of learning them and providing them. If this can be done with different reef crabs then we'd be sparing a lot of wild populations. That's a pretty good goal.
 

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there just isn't a lot of resources out there yet (as far as I can tell).
Yeah, there’s almost no info out there on pom pom crab culturing.
I have to ask how you know so much about this? Have you talked around with breeders?
I’ve done quite a lot of reading up on scientific aquaculture research about a number of different species (pretty much anything I can find info on - fish, invert, coral, etc. - I read about).
What makes you think Parvocalanus crassirostris is a good starting choice? Is there some kind of understanding of which nutrients crab larvae require to grow?
Parvo is my go to suggestion for species that either haven’t been bred yet (especially if attempted in the past, as I know pom poms crabs have been) or if they’ve only been aquacultured recently. My reasoning is that rotifers and Artemia nauplii have been the go-to staple for breeding for decades (BBS especially for crabs), so it’s practically guaranteed they’ve been tried before unsuccessfully (it’s possible they work as a first feed, then hit a bottleneck though). Beyond that, Parvo pods are small enough to be used in place of rotifers (pretty well all other pods on the market at this point are too big), and the other pods on the market are both typically easier to culture than Parvocalanus pods and have been in use by professional aquaculturists for longer now, so the odds are relatively high that someone has tried them before unsuccessfully as well. Again, these may work, be the right size, move the right ways, etc. for these, but I’d assume not (at least for the first feeding).

Generally speaking, as far as the nutrition goes, most crabs (such as decorator crabs, arrow crabs, mud crabs, fiddler crabs, Mithraculus spp., etc.) have done well from a larval-survival perspective when fed either brine shrimp nauplii exclusively or both BBS and rotifers (not rotifers alone). So, feeding BBS makes sense, as it seems to meet most crabs nutritional needs at least relatively well. However - given my assumption above - I’m assuming something is wrong with that diet for these guys specifically (at least, at some point).

Relatively little crab aquaculture research that I’ve looked at involved copepods (though looking back at the decorator crab research, they were offered Parvocalanus and did worse on a Parvo and BBS diet than just on a BBS only diet, so it may not be a great first feed suggestion for crabs). That brings me the quote and questions below:
Apparently they eat a lot.
Have you found anyone who has confirmed these guys eating something as larvae? If so, what were they feeding, and when (meaning, from what days post hatch and for how many days post hatch)? Do you have any links to their efforts that I could read?

If they’re already shown to be eating specific foods, them looking into why those foods didn’t work is a good starting point: was it not meeting their nutritional needs? was it too big? did it not move in the right way to encourage predation? was it in the right part of the larval rearing tank for the larvae? was there enough of it for the larvae? was there too much of it for the larvae (this one sounds odd, but having too many feeders in a tank can cause serious issues for some species)? Etc.

If you can narrow down why it doesn’t work, then you can try to figure out ways around the issue.
All the rearing tanks I've seen for inverts are bare bottom. Is this a requirement, or do you think they can settle on substrate?
Not a requirement, but barebottom tanks have a few benefits in larval rearing (cheaper, easier to keep clean, easier to see the larvae, etc.), so most people run them. That said, as I mentioned before, some species literally require substrate to settle on (and some need very specific substrates, such as specific species of diatoms), so it depends a bit on the species and on how much labor is being put into the rearing (some species get graded into different tanks based on size at different ages - this is commonly done to avoid cannibalism - so the specimens may only have a settlement substrate in a specific tank, but moving specimens between tanks every few days is obviously pretty labor intensive/time-consuming).

Again, the settlement cues vary from one species to another, and some have very specific cues needed while others just settle on their own. With situations like this one where settlement cues aren’t known, it may be wise to try one batch with none and then branch out from there to see if they need a specific cue.
 
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davidflagg

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Yeah, there’s almost no info out there on pom pom crab culturing.

I’ve done quite a lot of reading up on scientific aquaculture research about a number of different species (pretty much anything I can find info on - fish, invert, coral, etc. - I read about).

Parvo is my go to suggestion for species that either haven’t been bred yet (especially if attempted in the past, as I know pom poms crabs have been) or if they’ve only been aquacultured recently. My reasoning is that rotifers and Artemia nauplii have been the go-to staple for breeding for decades (BBS especially for crabs), so it’s practically guaranteed they’ve been tried before unsuccessfully (it’s possible they work as a first feed, then hit a bottleneck though). Beyond that, Parvo pods are small enough to be used in place of rotifers (pretty well all other pods on the market at this point are too big), and the other pods on the market are both typically easier to culture than Parvocalanus pods and have been in use by professional aquaculturists for longer now, so the odds are relatively high that someone has tried them before unsuccessfully as well. Again, these may work, be the right size, move the right ways, etc. for these, but I’d assume not (at least for the first feeding).

Generally speaking, as far as the nutrition goes, most crabs (such as decorator crabs, arrow crabs, mud crabs, fiddler crabs, Mithraculus spp., etc.) have done well from a larval-survival perspective when fed either brine shrimp nauplii exclusively or both BBS and rotifers (not rotifers alone). So, feeding BBS makes sense, as it seems to meet most crabs nutritional needs at least relatively well. However - given my assumption above - I’m assuming something is wrong with that diet for these guys specifically (at least, at some point).

Relatively little crab aquaculture research that I’ve looked at involved copepods (though looking back at the decorator crab research, they were offered Parvocalanus and did worse on a Parvo and BBS diet than just on a BBS only diet, so it may not be a great first feed suggestion for crabs). That brings me the quote and questions below:

Have you found anyone who has confirmed these guys eating something as larvae? If so, what were they feeding, and when (meaning, from what days post hatch and for how many days post hatch)? Do you have any links to their efforts that I could read?

If they’re already shown to be eating specific foods, them looking into why those foods didn’t work is a good starting point: was it not meeting their nutritional needs? was it too big? did it not move in the right way to encourage predation? was it in the right part of the larval rearing tank for the larvae? was there enough of it for the larvae? was there too much of it for the larvae (this one sounds odd, but having too many feeders in a tank can cause serious issues for some species)? Etc.

If you can narrow down why it doesn’t work, then you can try to figure out ways around the issue.

Not a requirement, but barebottom tanks have a few benefits in larval rearing (cheaper, easier to keep clean, easier to see the larvae, etc.), so most people run them. That said, as I mentioned before, some species literally require substrate to settle on (and some need very specific substrates, such as specific species of diatoms), so it depends a bit on the species and on how much labor is being put into the rearing (some species get graded into different tanks based on size at different ages - this is commonly done to avoid cannibalism - so the specimens may only have a settlement substrate in a specific tank, but moving specimens between tanks every few days is obviously pretty labor intensive/time-consuming).

Again, the settlement cues vary from one species to another, and some have very specific cues needed while others just settle on their own. With situations like this one where settlement cues aren’t known, it may be wise to try one batch with none and then branch out from there to see if they need a specific cue.

This is a thread where someone tried to raise pompom crabs to adulthood (apparently not their first attempt). Based on their experience, the larvae apparently ignored bbs almost entirely. They did however eat rotifers, copepod nauplii, and especially ciliates. The ciliates seemed to encourage hunting behavior - they'd use their tails to propel themselves through the water to catch prey. They were also accepting tetraselmis at around the 6 day mark.

They settled on the bare tank bottom at roughly 2 weeks, where they continued to chase things (supposedly more ciliates). No updates were given afterward, so there's no knowing if the person had any true success. What they did find though was that underfeeding was the culprit for larval deaths pretty much every time. A larger container size and higher zoa/zooplankton densities raised their chances for success. Their "larger container" though was 1.5L. Tiny compared to an actual reef tank. I'd imagine success would be much more likely in a nano tank with no predators.




Here is another later thread with the same person trying again. Here they confirm the crab larvae feeding on rotifers and copepod nauplii for about a week. Then crashed. They suspect inadequate spacing this time (they're still using very small containers). Interesting note they made - apparently the larvae need to retreat to a sheltered area to molt, which suggests an empty tank won't cut it.
 

Paul B

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I personally never heard of anyone raising any kind of crabs in a home aquarium. Crabs spawn constantly. I see it all the time in my tank and may even see the fry just after they hatch, but they never live long. My tank is very old and not very clean so you would think something would survive, but I have never seen a baby crab.

In the sea they hang out at the surface and become part of the plankton where they eat very tiny foods. Probably smaller than rotifers like single celled algae.

But good luck. I hope you get a bumper crop of Pom Pom crabs, :beaming-face-with-smiling-eyes:
 

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Some really good observations in those links. The fact that some settled tells me that whatever they were eating worked for them, so I'd say Phyto, Rotifers, Ciliates, and Copepod nauplii are a good place to start food-wise; with the note that they seem to show hunting behavior for the ciliates, trying to find a pod species that moves similarly to a ciliate may be a good idea.

Either way, you could try one food at a time, or (my suggestion if you're up for culturing that many things at once/running multiple larval-rearing tanks at once) you could split one batch of crab zoea into multiple testing conditions, offering each group different foods to see which works for them (at least for certain days). Basically, you'd offer each group one food item, and any groups beyond that you would offer multiple food items at once in the combinations that you think are most likely to succeed.

Providing sheltered areas to molt for the settled young could be tough if you get a lot of them surviving, but it shouldn't be too bad if you only have a few; basically just set up a bunch of little caves for them to hide in at the bottom of a tank (depending on the size of the settled crabs, you could potentially make these out of eggcrate; if they're too big for that, you could pretty easily use pvc pipe halves) - you may want to move the settled young into a grow-out tank separate from the larval-rearing tank for that so that you can more easily manage the food populations in the larval-rearing tank while having enough room for the caves in the grow-out tank.
 
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davidflagg

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I personally never heard of anyone raising any kind of crabs in a home aquarium. Crabs spawn constantly. I see it all the time in my tank and may even see the fry just after they hatch, but they never live long. My tank is very old and not very clean so you would think something would survive, but I have never seen a baby crab.

In the sea they hang out at the surface and become part of the plankton where they eat very tiny foods. Probably smaller than rotifers like single celled algae.

But good luck. I hope you get a bumper crop of Pom Pom crabs, :beaming-face-with-smiling-eyes:
How often do crabs breed-? I thought it was only after a molt, but if they're doing in constantly then maybe not.

Next time you see some larvae, try and throw in some extra microbial food to see what happens. You could be sitting on a tank with goldilocks conditions.
 
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davidflagg

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Some really good observations in those links. The fact that some settled tells me that whatever they were eating worked for them, so I'd say Phyto, Rotifers, Ciliates, and Copepod nauplii are a good place to start food-wise; with the note that they seem to show hunting behavior for the ciliates, trying to find a pod species that moves similarly to a ciliate may be a good idea.

Either way, you could try one food at a time, or (my suggestion if you're up for culturing that many things at once/running multiple larval-rearing tanks at once) you could split one batch of crab zoea into multiple testing conditions, offering each group different foods to see which works for them (at least for certain days). Basically, you'd offer each group one food item, and any groups beyond that you would offer multiple food items at once in the combinations that you think are most likely to succeed.

Providing sheltered areas to molt for the settled young could be tough if you get a lot of them surviving, but it shouldn't be too bad if you only have a few; basically just set up a bunch of little caves for them to hide in at the bottom of a tank (depending on the size of the settled crabs, you could potentially make these out of eggcrate; if they're too big for that, you could pretty easily use pvc pipe halves) - you may want to move the settled young into a grow-out tank separate from the larval-rearing tank for that so that you can more easily manage the food populations in the larval-rearing tank while having enough room for the caves in the grow-out tank.
Yes, they uncovered some very helpful info. Rotifers, copepod nauplii, and ciliates are confirmed successful feeders for crab larvae. Apparently all other factors - temperature, lighting, flow, water chemistry - don't need extremely unique conditions. The fact that they settled on the bottom is very encouraging, it's just confusing how they still crashed afterward.

I'm wondering if the truly damning thing about all these experiments is the isolation. Dragging the larvae from their breeding grounds to a separate cramped tank with lab-like conditions might be tossing out all the complex factors that trigger their hormones. I don't believe that these breeding tanks can mimic the open ocean at all. If food isn't a problem now, then the rest might be environment - a larger tank with normal reef conditions might just do the trick. It would take care of sheltering too.

The fact that inverts like these might be able to be captive bred to preserve wild populations is a huge personal motivator here. I've seen the hobby do good things for all kinds of species. Getting rid of the hobby's negative parts would be great.
 

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a larger tank with normal reef conditions might just do the trick. It would take care of sheltering too.
You just need to make sure there's nothing there that would prey on the young crabs.
Apparently all other factors - temperature, lighting, flow, water chemistry - don't need extremely unique conditions. The fact that they settled on the bottom is very encouraging, it's just confusing how they still crashed afterward.
Yeah, reading through the threads, they don't seem too difficult at all (it's actually surprising to me given how easy they apparently were to get to settle that I haven't seen these captive bred); it's possible that they still crashed because of nutrition deficits from their previous larval stages (this has been known to happen in some species), or because they need something post settlement to fully settle (like how hermit crabs need shells to fully settle/survive settlement) - I'd guess this would be related to their "pom pom" anemones if this is the case, but I don't know for sure.
 

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How often do crabs breed-? I thought it was only after a molt, but if they're doing in constantly then maybe not.
They do spawn when the female molts, But they do that all the time, more often when they are young.
 

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