Crayfish diseases

I was trying to start a colony of marmorkrebs for sunfish food. One batch of young had seven grow to near adult size and should have been nearly breeding age when the whole colony was abruptly wiped out. I now have only one individual from a later batch of eggs, which has survived in the same tank and seems to be doing fine.

Eight crays were housed in a 30 gallon tank with crushed coral substrate, lava rock and pieces of 1" PVC pipe for shelter. Tankmates were some male Gambusia and a couple clams. The tank had previously housed 4 native crayfish which were moved out the same day I added the marmorkrebs. All the crays became lethargic at about the same time (noticed on the same day). Some were already dead, some were just very lazy. I moved a couple into different tanks where one died the same day and another, the one I originally bought, survived another two weeks before it too died. It remained lethargic in its new home, however. I saw no signs of external parasites, but I don't know enough about their internals to make a good inspection. I didn't see anything grossly out of the ordinary when I dismembered the dead for fish food. The last one to die is still in my freezer and could be inspected for parasites if somebody can tell me exactly what to look for. I also noticed when removing the crays that their shells felt a little soft and had the slightly slimy texture as though they were preparing to molt.

I'm wondering if this could have been a disease transferred from the wild crays, or if anyone has any idea what this combination of symptoms might be.

All at once indicates water quality. Can you detect a rotten like smell? Check nitrites and nitrates. Could copper have introduced?

I hadn't tested nitrate, but nitrite was zero, and all the fish are fine plus the smallest crayfish is still in there doing well. The water smells fine.

I'll investigate for possible sources of copper, but nothing has been intentionally added since the tank was set up six months ago.

Edited by gzeiger, 20 October 2009 - 09:52 PM.

I hadn't tested nitrate, but nitrite was zero, and all the fish are fine plus the smallest crayfish is still in there doing well. The water smells fine.

I'll investigate for possible sources of copper, but nothing has been intentionally added since the tank was set up six months ago.

Nitrate can be a problem with some crayfishes, yet not be a problem for fishes.

Did the muscle, even when crayfish alive appear brownish? Muscle could be seen in abdomen from below.

Delayed mortality following transfer may also be due to a pathogen or nutritional problem.

When my crayfish stocks are losing to a pathogen or parasite, I typically destroy whole population or attempt to cut losses with major water changes. I did not attempt use of chemotherapeutics since did not determine organism involved.

Nutritional problems affect faster growing animals first. Vegetable matter in diet goes a long way towards meeting nutritional requirments that can not be consistently met with high quality pellets or sometimes even live zooplankton. I have been able to kill fast growing crayfish by feeding only live baby brine shrimp or live water fleas. Adding a little plant material, i.e. alfalfa meal, stopped most mortalities and promoteed natural color.

Thanks for your help. Nutrition may be it. I was feeding a lot of meat, with the crayfish basically eating whatever fell past the fish. I tried for a while to feed Spirulina wafers, but I probably forgot to provide that for some time. I had no idea that could kill them so fast.

Muscle tissue of all deceased was white as normal. I didn't look at that on any of them before they died.