Discolouration on hermit crab limbs

[TeaDragon]

1. What kind of substrate is used in your tank and how deep is it?
10cm/4inches. I use play sand and coco fiber, mixed to the recommended ratio, but can't remember what that was.

2. Do you have gauges in the tank to measure temperature and humidity? If so, where are they located and what temperature and humidity do they usually read?
My gauge is located at the centre of my tank. Currently reads 21C and 75%. Having trouble heating the tank this winter.

3. Is a heat source used in the tank? If so, what?
3 heatmats, 2 smaller ones on a side of the tank and a large one on the back. Ordering another large one for the back of the tank, which will then cover the entire back of the tank.

4. What types of water are available (fresh or salt) and how is the water treated (what brands of dechlorinator or salt mix and what ratio is used to mix it)?
Fresh and salt water is provided. I use Jurassisafe and API for conditioner, as I can't find one conditioner that targets heavy metals, chroline, chloramine and the nitrates and nitrites.
I currently use hermit crab salt for the salt water, as I haven't found instant ocean here yet.

5. What kinds of food do you feed and how often is it replaced?
Assortment of food. Sardines, powdered, additive free food, fresh fruit and veggies, olive oil, molasses occasionally. Leaf litter, wood, cuttlebone and sphag moss are always available. Green sand and worm castings are in transit atm.
Swap out the food once every 3 days for dry food and usually once a day for fresh foods.

6. How long have you had the crab and what species is it, if known?
I've had Gourden 6 months. Knoppie for 2 months. TBN for 2 weeks. All crabs are Aussies.

7. Has your crab molted, and how long ago did it happen?
Gourden moulted on 3/6/2021. Knoppie was buried for 3 weeks not too long ago, tho I think this was just pps. TBN is underground still.

8. What type of housing are the crabs kept in, what size is it and what kind of lid is on the housing?
A reptile one 40gal. Lid is mesh with clingwrap.

9. How many crabs are in the tank and about how large are they?
Gourden is 5cm diameter, Knoppie and TBN are 3cm in diameter.

10. How many extra shells are usually kept in the tank, if any?
10

11. Have there been any fumes or chemicals near the crabitat recently?
Don't think so.

12. How often do you clean the tank and how?
Pick up old, spilt food when I change their bowls. Water dishes get changed every 2 weeks. Have isopods and springs, so they pick up the other waste.

13. Are sponges used in the water dish? If so, how are they cleaned?
None

14. Has anything new been added to your crabitat recently?
Lacewing larvae to deal with some scale on the bromeliads.

15. Is there any other information you would like to share that might be helpful (anything that is regularly part of your crab care, playtime, bathing, etc.)?
No

16. Please describe the emergency situation in detail.
So, I noticed that Knoppie has some discolouration on his legs and pinchers. Dark coloured blotches on his pinchers. Almost looks like bruising. He is also missing a leg on his left side, that I only noticed a few days ago. I don't think he had a missing leg when I bought him.
I looked at Gourden too and he seems to have some purple marks on his big claw, which are not nearly as bad as Knoppie's. I'm very stressed about it.

Here you can see the two spots of discolouration on Gourden's claw. I will attach a photo of Knoppie asap, but he's vanished in the cage lol.
Please help.

[aussieJJDude]

I may of missed it, but is the diameter (size of crab) inclusive of shell or leg span?

[TeaDragon]

I may of missed it, but is the diameter (size of crab) inclusive of shell or leg span?

Yes, sorry, it is the diameter of the shell

[TeaDragon]

So, while not the clearest, managed to get some photos of Knoppie, who has the discolouration the worst.

Here are the spots on his claws.

Here is the only leg on his left side, with the worst of the discolouration. It looks grayish.
I don't know how I didn't notice this earlier, I feel super bad.

[DragonsFly]

[Following. Could it be something introduced by the most recent addition?]

[TeaDragon]

[Following. Could it be something introduced by the most recent addition?]

The newest guy had no such markings, from memory, and burrowed right away. Did not even see the other crabs. TBN and Knoppie, the one who has it the worst, came from the same place. I'm thinking Knoppie brought the disease home, but I just didn't notice, as he also buried himself as soon as I put him in the tank.
They seem fine though. Very active at night and eating lots of cuttlebone.
The spots aren't natural colouration, are they?
Hoping to find a solution soon. Or at the very least, an answer.

[DragonsFly]

I've never had Aussies, so I really don't know if it might just be natural coloration. I was just following this thread to find out what our resident Aussie expert thinks. AussieJJDude, what do you think???

[wodesorel]

I don't like this. I've been staring at this since you posted it trying to figure out if it's worth the scare to say it could be something infectious.

My suggestion would be a full substrate change out, and then monitoring. With luck it goes away the next time they molt. I've had very similar but not exactly the same markings (possibly due to the difference in species and supplies) and the substrate change nipped whatever it was before it got worse. Once it was too much added salt, a couple times I think I just got a bad bag of sand.

If it continues spreading after the change and after they molt, I would be leaning heavily towards bacterial or fungal, and we do not have good treatment answers for those.

[TeaDragon]

I don't like this. I've been staring at this since you posted it trying to figure out if it's worth the scare to say it could be something infectious.

My suggestion would be a full substrate change out, and then monitoring. With luck it goes away the next time they molt. I've had very similar but not exactly the same markings (possibly due to the difference in species and supplies) and the substrate change nipped whatever it was before it got worse. Once it was too much added salt, a couple times I think I just got a bad bag of sand.

If it continues spreading after the change and after they molt, I would be leaning heavily towards bacterial or fungal, and we do not have good treatment answers for those.

Hey there, thank you so much for getting back to me. That's terrible to hear ugh. My newest crab has buried himself, should I wait until he resurfaces or just dig him up? Will rinsing, then freezing/baking the substrate make it reusable? I also have live plants, will they be savable? This is quite upsetting, as I have a very healthy population of isopods and springtails in that tank. Also had to chuck out a bunch of my isopod tubs and land snails this week due to phorid flies. When it rains, it pours.
Could phorid flies be eating my crabs? I heard some varieties can do that, though I think the ones I found were just after the decaying matter in my isopod tubs.

I've heard about herbal bacterial baths while trying to figure out what was wrong with my crabs. It was on the Crab Street Journal. Is that worth trying if the sub change shows no positive results?

Again, thank you for getting back to me. Devastating news, but a possible solution.

[wodesorel]

It sounds like you have an awesome tank, so if you don't want to go nuclear yet, might I suggest keeping an eye on the progression for now and then isolating future molters to fresh substrate. That way you can keep things going for your current molter and keep the tank intact until you know for sure it will work.

I don't think anything looks horrible right now, the exo is intact. I've never used the medicinal baths myself because I believe it's too much stress to continually treat them, and stress itself can make an illness much worse in animals. It's usually a tradeoff between being helpful and being too stressful and we don't have any hard data on the herbs having an effect.

Phorid flies go after dead and rotting things. There are fly species whose maggots eat living flesh but it wouldn't be half-hearted like these spots, they eat to kill. So I don't think those are the issue, though they are a pain to deal with!

Do you have old photos to go back and see when it started? If they molted into it, they will probably molt out of it in new substrate. Is there also a chance that they came with the marks and are in the process of molting out already?

I'm honestly not sure if cleaning the sand will do it, it might. When it was too much salt in my huge tank, I tossed like 75% of it and mixed what was left with fresh substrate and everything went fine for them afterwards. When I had iso tanks with new crabs who molted into spots I didn't even bother fussing, I just tossed the bag or two of sand out and got fresh for a few bucks- but I have a wookie for a husband and he does the heavy lifting so it wasn't a huge project. I started out with fish, and the first thing aquatic vets do when there is weird trouble is flush it out with as much new water as possible. I've always applied that to the crabs and my other critters and it's brought good results.

[TeaDragon]

I started out with fish, and the first thing aquatic vets do when there is weird trouble is flush it out with as much new water as possible. I've always applied that to the crabs and my other critters and it's brought good results.

This really helped put me at ease --- Thank you for that. I'll remember this for the future.

You make lots of very good points. It's reassuring to hear about the phorid flies too. I've heard about them killing wounded tarantulas and was very worried.

You also just mentioned isolating future molters, by that do you mean waiting for pms to show up and then chucking the premolt crab in an iso tank with new sub?

I didn't even consider the fact that they could be moulting out of the spots. I'll keep an eye out in case it gets any worse. I'll document the progress with photos so that I can tell if it's getting worse. If it does, I'll do as you did and replace the substrate.

Again, thank you so much for taking time out of your day to help. It's really helping me keep afloat today!! It's so good to be able to talk to experienced crabbers. Thank you <3