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Red Claw Crabs (
Perisesarma bidens) are a brackish species and out of my typical wheelhouse, but I'm happy to help if I can.
A very important note to start: these crabs are noted as being highly aggressive, and they are known to kill and cannibalize each other in aquariums. The males are noted as being more likely to actually fight. Generally, I would recommend either only keeping one or keeping either a male/female pair or a female/female pair, but these crabs are also noted as being difficult to sex accurately, so that a pair may be tough here.
These crabs live in mangrove sand/mudflat areas; they're known burrowers, but they also reportedly like to have natural hides (overhangs, crevices they can climb into, mangrove roots to hide in, etc.),* so a fine sand bottom with plenty of naturalistic hiding places is a good start. I have also heard that they need land available,** and this is, to my knowledge, supported by the respiratory system anatomy,*** so I would be sure to include a way for them to get up out of the water into similar hides if they want (ensuring that they have an easy way to get back in the water no matter where they go in the tank). Something like a mudskipper aquarium may be appropriate inspiration for the tank setup.
For the brackish water, I'd probably aim for around 18 ppt/1.0135 sg for the salt levels, but I don't know what would be ideal for the species, and it may change depending on their life stage (to say nothing of how much salinity levels change in the wild in mangrove forests).
P. bidens has had it's diet analyzed via gut contents (unfortunately, these did not go into specifics on what true plants these ate) and some very, very basic experiments (I take issue with at least one or two of these, but that's honestly irrelevant). Anyway, they primarily eat "plant material" and "inorganic detritus" (making up ~85% of the crab's diet, with the makeup being ~65% and 20% respectively), with a little bit of macroalgae, microalgae, "animal material," and "unidentified material" in the wild,*** so something mimicking that may be wise. However, the one experiment I came across (also describe in the *** source) that tried to offer them a decent imitation of their natural diet, including leaf litter and other plant parts from various species of mangrove plants (including the Tall-stilt Mangrove,
Rhizophora apiculata; the Loop-root Mangrove,
Rhizophora mucronata; and the White/Grey Mangrove,
Avicennia marina) noted that the crabs reacted very quickly and nervously to any sort of mechanical disturbance in the aquaria they were kept in - so while they likely eat these sorts of things in the wild, it seems the crabs may have been too nervous/not adapted enough to eat them in captivity. Some other mangrove species that may be worth trying as well include:
Kandelia obovata, Ceriops tagal, Avicennia alba, Avicennia officinalis, Avicennia rumphiana, and
Bruguiera gymnorhiza.
If I had access to all of the above but could only pick one for this species, I would go with
Kandelia obovata, as while I can't confirm that they eat the leaves, these crabs have been kept in tanks for breeding purposes successfully with the leaves offered as their food item (so I have strong reason to suspect they feed on them).****
Assuming you don't have access to a relatively large number of mangrove leaves, twigs, etc. from, it may be worthwhile to try and find a more readily available alternative, but I'm not sure how suitable the standard alternative feeds like algae pellets or lettuce might be for these critters. Maybe
@Jay Hemdal would have some insight there or into appropriate alternatives?
As far as equipment goes, I don't think these would be too demanding:
-Flow/aeration like from a powerhead, gyre, pump, and/or air stone.
-Lighting may not even be necessary for the crab (lighting is important for some critters, but not so much for others), but if you're wanting either to imitate their natural habitat better, stimulate spawning (these crabs rely on light cues for spawning),**** or grow something that's photosynthetic (like plants, algae, coral, etc.), then I would pick up some some lights. What you want to grow with the light changes what I would specifically recommend, but the quotes below can help you get started, and I'm happy to answer questions if I can (a few general rules: more blue and less red for corals; with true plants, blue is for growth and red is for flowering; if the lights can grow other things, they can grow algae):
(Quick technical note about PAR and PPFD for anyone who cares: the "PAR" values people talk about are technically the PPFD values:)
Some people prefer metal halide lights, others LEDS, others T5's - they all work when done correctly. As a general rule, either 12 hours of light and 12 hours of dark (which these crabs have been kept with for spawning before)**** or 14 hours of light and 10 hours of dark are recommended.
-Filtration is honestly more of a personal choice than most things in the hobby - the point of filtration is basically just to remove excess nutrients (for our purposes, primarily nitrate and phosphate) from the water. Mechanical filtration (like canister filters, HOB filters, skimmers, etc.) can be used for this, as can biological filtration (live rocks/sand, refugia/cryptic refugia, algae reactors, etc.) or a combination of the two. I personally am biased toward biological filtration methods as they're friendlier to pelagic larvae (and aquaculture is a big interest of mine), so I'm not much help as far as specific equipment goes for filtration purposes, but there's plenty of info here on R2R to help with that, and you can always start your own thread asking for help with it too.
Other considerations:
-You'll need temperature regulation, so most likely at least a heater (and possibly a chiller too, depending on your local climate); a controller (like an Inkbird controller or similar) is generally recommended as well in case of heater malfunctions (lots of tanks have been wrecked by heater malfunctions roasting them). Without knowing the specific critter's ideal temperature range, 77F-81F is generally a safe range to aim for, and I know these crabs have been kept at 77F before in breeding tanks successfully,**** so I'd recommend that range here.
-I always personally recommend an RO/DI system (it isn't always needed, but it ensures clean water for the tank; you can buy distilled water or similar instead, but it generally is less cost effective long-term; I don't recommend getting water from your LFS - I've heard too many stories of people having issues with LFS water).
-Depending on your circumstances, you may need to consider how to keep the tank running in an extended power outage (things like generators, battery backups/battery powered backups, etc.).
-Water parameters like mentioned in one of my earlier posts:
With crustaceans, some parameters you may want to check include:
-Calcium
-pH
-Nitrate
-Phosphate
-Alkalinity would probably be good to test as well.
*Source:
**Source:
***Source (I had to request this one from the source; it was free and easy to access, but it makes it difficult to share easily):
THE POPULATION DYNAMICS AND FEEDING ECOLOGY OF THE MANGROVE CRABS METOPOGRAPSUS FRONTALIS (GRAPSIDAE) AND PERISESARMA BIDENS (SESARMIDAE), IN HONG KONG
The author is Poon Yiu Nam David.
****Source:
