Shell Rot & Treatment

General/Background information: One of the more common diseases to affect most crayfish, many owners have or will see this disease at some point. This disease is also know as box burnt disease, shell rot, brown/black spot, burn spot and rust disease. And is caused by one of two fungu. The first of the two (which is the more deadly of the two) is Ramularia, having much higher death rates. The second is Didymaria, which causes smaller lesions.

When larger lesions and injuries are present, the crayfish's shell has been breeched and this gives microorganisms (bacteria, fungi or protozoans) an opportunity to invade the injury. At such a point, things will begin to eat into the shell and once all three layers have been penetrated they will start to eat the soft layers (the new shell). Since the outer and inner layers are fused together, this can prevent the crayfish from molting which will result in death. This is often seen as when a crayfish gets stuck in a molt.

Signs of the disease: Brown/Black or Rust colored lesions appear on the carapace. Giving it the appearance of rust, burnt flesh and decay.

Cause of the disease: Other causes of this disease include the stress of capture, high temperatures along with high suspended nutrient, over-crowding and poor water quality (this being the biggest and most common cause). Crayfish are very tolerant of poor water quality but the biggest risk is poor substrate. When your excess foods get trapped in your substrate it becomes anaerobic, which allows further infection from pathogens and your crayfish sits in them all day and night.

Prophylactic treatment: Clean your tank and substrate regularly! Keep water conditions and housing arrangements at an acceptable level!

Treatment: For minor injuries, you can use Melafix. However, more than likely it will not do anything (and may not even slow down the process). And one should keep in mind that Melafix is entirely organic and can act as food source for certain types of bacteria. This leading to a bacteria boom in the tank. So, personally, I would recommend not using Melafix for anything and finding alternative treatments to any issues you may have. That aside, you can use the following treatment for Shell Rot:

"1.) Grab a set of scales and measure out 35 grams of salt.
2.) If you don't have micro scales a good teaspoon is around 4.7grams, so 7 nice teaspoons will do.
3.) I don't mind what salt you use, personally I prefer pool salt.
4.) Throw that in 250ml of boiling water and stir in until dissolved.
5.) Then take 750ml of water from your crayfish's tank put it in a 4 litre ice cream container or something similar with high sides.
6.) Add the dissolved salt solution to it and stir again.
7.) Drop an air stone to keep the water nice an aerated.
8.) Set up an alarm clock/timer to 10 minutes.
9.) Drop your crayfish in and make sure it can not escape.
10.) Go do some maintenance on the tank.
11.) Come back and remove your crayfish when the alarm goes off.
12.) Repeat every 3 days as needed until next moult or lesions are "bleached out".

Cure: Currently, there is no cure for this disease. Your best bet is to use the process above to slow down the infection until the next molt, where it will be removed from the crayfish provided the soft layer (new shell) has not been jeopardized.

Source: crayfishmates.com