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Gus · 01-08-2008, 11:52 AM

Shell Disease is one of the more common diseases effecting crayfish. No doubt most of you have seen this and many of you do not know how to treat it. Knowing how to treat shell disease, requires you know a little about what this little nasty is that is rotting away your crayfish's shell.

Other names shell disease goes by is, box burnt disease, shell rot , brown spot, black spot, burn spot or rust disease. The cause is primarily an opportunistic bacteria that will invade some small injury on the crayfish. You will have seen a small rusty spot on the end of an antenna that has been nipped off or broken. This is the start though quite often with a small injury like that it will not spread any further and is removed with the next moult.

With larger injuries the crayfish's armor is breached and gives the opportunity for microorganisms like bacteria, fungi, or protozoans to start their invasion. At this point these nasties basically eat into the shell (chitin) and here in lays the problem for the aquarium enthusiast and aquaculturist alike. What happens is the bacteria eat through the outer three layers of the hard exoskeleton and start into the nice soft layer. This soft layer is the beginning of the next moult and then the outer and inner are "fused" together, which can prevent the crayfish from moulting. No moult, no growth, no grow = death. This is where the infected crayfish will get "stuck" in a moult.

There are other causes of this disease and they include, the stress of capture, high temperatures along with high suspended nutrient, over crowding and the biggest is poor water quality. 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 (no oxygen), which encourages these nasty little gram negative bacteria and your crayfish sits in them all day and night. Hint, clear your substrate regularly.

Below I have provided you with pictures of a Cherax destructor with advance lesions. Note the brown indents into the shell of the crayfish. These will start out as little brown to black spots no bigger than a pin head.

01-08-2008, 11:52 AM	#13
Gus Dragon Join Date: Feb 2003 Posts: 2,793	Shell Disease And Ugly Brown Spots, You will all have this at some point with crayfi Shell Disease is one of the more common diseases effecting crayfish. No doubt most of you have seen this and many of you do not know how to treat it. Knowing how to treat shell disease, requires you know a little about what this little nasty is that is rotting away your crayfish's shell. Other names shell disease goes by is, box burnt disease, shell rot , brown spot, black spot, burn spot or rust disease. The cause is primarily an opportunistic bacteria that will invade some small injury on the crayfish. You will have seen a small rusty spot on the end of an antenna that has been nipped off or broken. This is the start though quite often with a small injury like that it will not spread any further and is removed with the next moult. With larger injuries the crayfish's armor is breached and gives the opportunity for microorganisms like bacteria, fungi, or protozoans to start their invasion. At this point these nasties basically eat into the shell (chitin) and here in lays the problem for the aquarium enthusiast and aquaculturist alike. What happens is the bacteria eat through the outer three layers of the hard exoskeleton and start into the nice soft layer. This soft layer is the beginning of the next moult and then the outer and inner are "fused" together, which can prevent the crayfish from moulting. No moult, no growth, no grow = death. This is where the infected crayfish will get "stuck" in a moult. There are other causes of this disease and they include, the stress of capture, high temperatures along with high suspended nutrient, over crowding and the biggest is poor water quality. 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 (no oxygen), which encourages these nasty little gram negative bacteria and your crayfish sits in them all day and night. Hint, clear your substrate regularly. Below I have provided you with pictures of a Cherax destructor with advance lesions. Note the brown indents into the shell of the crayfish. These will start out as little brown to black spots no bigger than a pin head.