Mysterious die-off

[Varanus]

As documented here viewtopic.php?f=2&t=5799&start=15#p38448 I had a pretty nice Ghost shrimp tank (a twenty gallon long) going until a few weeks ago. The shrimp were healthy, breeding, and had an amazing amount of colors for ghost shrimp. I was quite proud given they were the only shrimp aside from my supershrimp that I'd had breed.

Then I decided to get them some companions for a more diverse and interesting tank, cambarellus shufeldtii, the cajun dwarf crayfish. A group of twenty of these fairly inoffensive tiny crayfish I ordered off ebay.

For the first week or so everything was fine. The crayfish were a lovely addition with their varied markings and hilariously tough behaviors. I never saw any fighting between them and the shrimp either. But odd things started to happen. I found a couple shrimp dead on the underside of the glass top. They had apparently jumped out of the water and gotten stuck to the underside of the glass, drying out and dying there. Unusual but I didn't think much of it.

Then both the shrimp and crayfish started dying in the water. Some of them seemed to simply die, but most of them seemed to go through an odd period of decline at least partly linked to shedding. The crayfish would shed partially, get stuck in their sheds (usually around their legs) and die after a few days, or get out of their shed (usually losing most of their limbs in the process) and still die a few days later (or I would put them out of their misery as they were very alive but unable to walk and thus feed). The ghost shrimp would lose legs, become lethargic and eventually die. Eventually I lost all the shrimp.

I have never had any of my invertebrates experience shedding problems before so it can't be that the water isn't suitable for them. As further evidence, I have a crayfish in another tank that has lived for years without a problem.

During the die off and afterward there was no detectable ammonia any of the times I tested (I removed the bodies quickly) and very low (if any) detectable nitrates. Furthermore, the nerite snails in the tank have not had a problem at all. The large population of copepods survived just fine as well.

Perhaps most mysteriously, two of the dwarf crayfish are still alive, perfectly healthy and intact, and have likewise shed at least once just fine.

I have since then gotten a batch of eight or so ghost shrimp, but the same die off has occurred, I think only one is left. It may just be a coincidence as I know it is common for these shrimp to die soon after purchase as they are not kept in good conditions (since the pet store expects you to just feed them to other animals), but to have such mass and consistent mortality seems odd.

I have also gotten some dwarf frogs since then and they have had no issues in the tank either.

The only thing I can think of is that it is some kind of pathogen that the crayfish brought with them that also infected the shrimp and that the two surviving crayfish somehow are immune to it.

Basically I'm writing all this to see if anyone here might have an idea as to what happened.

[mighty mite]

Shrimp can get sick, too. Mainly, they are susceptible to bacterial infection. Symptons are generally weird behavior. This seems like a strong possibility here. Treatment is metrozadole.

[Mustafa]

It could have been any of various causes. Freshwater invertebrates are a lot more sensitive than the Supershrimp. And since people do water changes there are a lot more chances to introduce all kinds of chemicals (chloramines, ammonia, kh and pH changes).

Having said that...those dwarf crayfish are pretty vicious with shrimp. They chase the shrimp constantly. Maybe a shrimp or two died and then caused a chain reaction due to a bacterial bloom/lack of oxygen or some other changes, such as gradual release of ammonia.

Frankly, lots of times the answer is just...I don't know! I'm guessing it's a combination of the two reasons above.

What is your kh and gh? (if you still have this tank, otherwise just your tap water).

[Varanus]

Sorry for not replying, forgot all about this topic and assumed no one else would reply to it.

Anyway the tank has gone through some changes. All but one crayfish eventually died (as did the nerite snails, but the copepods are fine), and I later added some amano shrimp for algae control as a later attempt to put nerite snails in failed. The amanos have done very well, not a single death in the several months they have been in there.

I also ordered more shufeldtii crayfish and they have done markedly better over these past few months than the previous batch. Some have died from failed molts or after molts, but most molt just fine (and the shrimp have never had trouble molting). I even saw one pair mating, so hopefully they will breed successfully. Whatever caused the mass die off seems to be gone from the tank.

Having said that...those dwarf crayfish are pretty vicious with shrimp. They chase the shrimp constantly. Maybe a shrimp or two died and then caused a chain reaction due to a bacterial bloom/lack of oxygen or some other changes, such as gradual release of ammonia.

Hmm, I never saw any chasing with these, only aggressive reactions if they were prodded unduly by ghost shrimp, they mostly ignored each other. The shufeldtii are supposed to be pretty mild-mannered by crayfish standards.

Likewise I haven't seen any aggression toward the amanos, but they're about twice the size of most of the crayfish anyway.

What is your kh and gh? (if you still have this tank, otherwise just your tap water).

I used a test strip so it may not be fully accurate, but the kh seems to be between 40 and 80, the gh between 60 and 120. I also have a piece of cuttlebone in there in case more calcium is needed.

[Mustafa]

The thing with crayfish is that even if you don't observe them chasing around shrimp all the time, they constantly snap at them when the shrimp get close. The accumulation of such "minor" harassment causes stress to the shrimp..especially at night when the crayfish are more active. If you pay close attention you'll probably notice that the antennae of the shrimp are mostly snapped off in such tanks. That even happened to my red cherry shrimp that I had with my various dwarf crayfish species. The Cambarellus patzcuarensis are MUCH more aggressive than our native C. shufeldtii, though. Even so, my ghost shrimp never survived for long in crayfish tanks.

[Varanus]

I'll definitely move the amanos out then if I see any such signs. For now their antennae all seem intact. But nighttime harassment may indeed explain the die-off last summer, a build up of toxins from the stress escalating things.