Shell Disease in O. scyllarus Revisited (Dr. R. Caldwell)
I recently received another request for information about shell disease in Odontodactylus scyllarus (Peacock Mantis Shrimp) and I though it might be useful to post my response. For those of you who have seen this before - sorry!
Erosion of the cuticle is commonly called "shell disease" in crustaceans. There are probably many different causes. This really just describes the symptom which includes discoloration and eventual erosion of patches of exoskeletion. Why shell disease is common in O. scyllarus is unknown, but large males in particular seem particularly susceptible. It is not just a disease of the aquarium. I have seen many animals in the field with it. Another large burrowing species, Hemisquilla californiensis, also seem particularly susceptible. I have also seen it in large Gonodactylus chiragra. My impression is that larger smashers that don't molt very often are most likely to get it.
We don't know the cause or even the primary pathogen. Usually by the time you start to notice rusty brown discoloration of the cuticle - typically on the carapace or dorsal abdomen, erosion has started and there is a whole community of fungus, bacteria, protozoa, etc. feasting on the diseased tissue. Gradually the patches spread and deepen until they eat entirely through the exoskeleton. At this point the disease is usually fatal. It weakens the animal and/or makes it impossible for it to molt successfully.
I know of no "cure", but there are ways to treat the disease. It makes sense that antibiotic dips might help, but I don't have any information on this. Unfortunately, stomatopods are quite susceptible to chemicals like formalin and other treatments that are used for skin diseases in fish, so I would not recommend experimenting. The good news is that if the disease does not advance too far and the animal successfully molts, they can literally shed the disease and recover. This is one case where I would recommend immediately removing the molt skin and not allowing the animal to bury or eat it.
I have found a few things that help. First, water quality seems to be key. Be sure your nitrites and nitrates are low. Also, good circulation seems to help. O. scyllarus do well in fairly strong currents. (I've collected them in areas where the currents were ripping at 2 or 3 knots.) I have also found that uv sterilization of the water seems to slow the disease and also reduce transmission to other stomatopods. (Actually, I haven't done the experiments to prove that it is contagious. It is difficult to separate out various environmental conditions that might cause the disease from transmission from another animal.) Strong lighting also seems to cause problems. A deep, dark burrow (black or grey pvc pipe at least twice the length of the animal and just a little bigger in diameter is about right) also can help. A good diet is also important. If I have an animal that shows signs of shell disease, I usually start adding supplements such as "Selco" to its diet. This is one time that I recommend feeding the animal as much as it will eat. The more quickly it molts, the better the chance that it will get rid of the diseased tissue and recover. Just be careful to remove uneaten or buried food to maintain good water quality.
I wish I could offer more help, but in general I have found that if I catch the disease early, take care of water parameters, hook up a uv filter, reduce lighting, increase flow, and add supplements to the diet, the animals usually survive. Sorry if this sounds like the usual laundry list of aquarium care, but it seems to work.
- Dr. Roy Caldwell
Web Site Author: A. San Juan
Site Created February 3, 1998