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I am experiencing problems with my Dwarf Cajun Crayfish population. I have already searched the forum for similar material and read the articles on raising them so I have already taken some of the steps mentioned for maximizing beneficial growing conditions for Dwarf Cajuns.

I am going to add a little background information before I begin with the problem because maybe some detail of my set ups or other potential problem issue is apparent through this additional information. So if one wants to see the problem first before seeing the additional information please feel free to skip ahead.

Ill put the background info in quotes.

I have four tanks with Crayfish and Shrimp in it:

A 10 gallon tank with Red Cherries and an assortment of snails: Red Ramshorns, Tiny “Pond” Snails (decedents of a wild caught population), and some type of Malaysian Trumpet Snail or something that looks and acts nearly identical(decedents of hitchhikers). Plants: Some type of Aquatic Grass I don’t know the name of it, but when fully grown it looks like freshly sprouting Bermuda grass (the aquatic grass has very fine blades seems to send out shooters like bamboo does).
Substrate: Black Sand.

A 20 gallon tank with Marbled Crays (Marmorkrebs), the same assortment of snails, and the only plants in the tank are a few Ludwigia repens. I tried planting what I assume is Ludwigia repens. but the marbled crays tended to uproot them over time so I gave up on plants and just let them float in the tank. (maybe If I allowed a plant more time to establish roots it would dissuade the marbled Crays from their infrequent substrate re-managing)
Additional structures two pieces of medium sized drift wood.
Substrate: 1 part Black gravel 2 parts mix color gravel

A 10 gallon tank that served primarily as an experiment to witness how well Dwarf Cajun Crays managed themselves in the presence of a large breeding population of Guppies. Plants being what I assume is Ceratopteris Thalictroides and what I assume is Ludwigia repens.
Substrate: Black Sand

A 29 gallon tank which is the problem tank. This tank contains the vast majority of my Dwarf Cajun Cray population along with the undesirable less-red Red Cherry Shrimp taken from my ten gallon tank. This tank just recently contained four adult female guppies 1 adult male guppy and about 5 baby guppies, the problem though existed before these guppies were in the tank. Plant wise in this tank there is Java fern and what I assume is Ceratopteris Thalictroides and what I assume is Ludwigia repens.
Substrate: 2 parts Black Sand 1 part Black gravel

Common Factors in All Tanks:

Each tank uses a Whisper Power Filter or one that is nearly identical in construction.
Each tank varies a bit between 73-78 in the summer sometimes they creep a bit over 80.
Each tank has rocks from out in the yard. They appear to be nearly entirely composed of quartz.
Each tank has a dead living sponge in them [see Natural Sponges in Tanks thread in shrimp discussion for info].

Ok the problem…I feel the best way to illustrate the problem is to give a brief history of the tank….Starting with the good times up and through problems to present day.

The tank was “old” and about 1/3 of the substrate surface area was dedicated to growing Ludwigia repens. I liked this plant a lot because it grew slowly, densely, and vibrantly in near zero nitrate/nitrite conditions. There were also two pieces of “medium sized” drift wood. I purchased 5 Dwarf Cajuns and 10 Red Cherry Shrimp from Mustafa to put in this tank (anyone who has received animals from Mustafa will know that his experience and knowledge causes him to send very young, small animals). I don’t really recall how long ago I received these animals from Mustafa but it is under a year, perhaps approaching a full year.

The 5 Dwarf Cajuns grew very slowly and eventually I was able to determine their sex, 4 females and only 1 male. I grew increasingly frustrated with my Cajuns because they reached a size that I had seen others have successes with reproduction. My shrimp on the other hand were reproducing, but uncharacteristically slow. I researched guides and journals of Cajun keeping to try to determine what I was doing that impeded their reproduction. I thought that maybe my water was not hard enough to allow rapid growth for both species. I do not have good tools to give a clear indication of pH levels. I am restricted to pH paper. To address this perceived issue I added a small piece of coral to the tank.

I was impatient and did not see results in the next week or so and did more research. I found some claims of certain types of driftwood making the water more acidic. I did not know if my type of driftwood was the kind that would lower the pH but to be safe I removed the two pieces of driftwood and put them in another tank(the one that eventually my Marbled Crays were placed in). In hindsight the driftwood is likely perfectly okay because my Marbled Crays are reproducing out of control. I left the piece of coral in the tank.

By this time my Dwarf Cajun’s had become full sized adults without any carrying of eggs (like the max size 3.5cm or so). Then I witnessed few matings. I saw some carry eggs…but dropped prematurely. Finally one successfully delivered young….then all four of the females successfully delivered young… I had a Cajun explosion so I figured I would just keep up everything that I was doing…..

The population got so big that the Red Cherry Shrimp were under constant harassment many died from apparent injuries. I started taking some of the new adolescents Cajuns and testing them under other tank conditions. I put a few in with guppies to see first hand how they would handle it. Overall everything seemed fine with my Cajun supply.

I got a few infrequent deaths. As far as I can tell they were all full grown adults who died. I was not terribly worried because of how numerous the population was.


Then one day I had a “massive” die out of Cajuns 5 in one day…. I hoped that this horrible event was caused from their frequent battles maybe….I water changed and removed corpses….The next day 4 more were dead…. All of these were of about “breeding size” slightly smaller than full blown adults…..I cant think of anything noticeable that I did before the deaths that could have caused it.

Around this time I was having awesome success with sponges and shrimp in another tank so I thought that maybe adding a sponge would help this tank. I added a sponge and the dying seemed to fade away. There was still a good deal of Cajuns left so I still felt confident.

After a week or so without noticeable deaths I added a male guppy and some females. From my earlier experiment I found that the Cajuns as long as they weren’t infants could handle themselves around guppies. Since I only intended to keep these adult guppies in the tank till they had offspring I did not think it was a huge issue.

I have had relatively frequent deaths 1-2 Cajuns a week. The adult guppies have been removed and their babies have been removed. The deaths have remained the same though.


I am now down to a population of about 12+ in the 29 gallon tank. 4 Cajuns are left in the 10 gallon test tank. If these deaths continue I worry about losing my population.





The first thing I thought was water condition type problems but the Cherries have always done alright and since the addition of the sponge the Red Cherry Shrimp have been flourishing. So water conditions don’t entirely explain the deaths unless Cajuns are particularly prone to some water condition that Cherries are adaptable to…..



I really am stumped as to why these Cajuns are dying….if anyone has advise please distribute it generously!


In conclusion what would explain the following.

A slow, but not uncharacteristically so, development (probably not important).
Late production of offspring.
Sudden successful breeding all around. Population Boom.
Large die off….followed by frequent die off…. coupled with seemingly stagnant growth….none are reaching adulthood.
Feeding practices have been constant.




[PS: I read this over once…Im sorry I didn’t do it more but it is tiresome to be perfect...Additionally I tried to format it for the easiest read]

I don't know a lot about this species specifically, but I didn't see anything about air stones or anything to help with the gas exchange. Quite often crayfish will lay to their side die "from no apparent reason" when they can't get enough oxygen. It is usually in numbers at a time if there are more crayfish than the oxygen in the tank can support. After enough have died, there wouldn't be a lack of oxygen for a while, perhaps until more of the babies got to a larger size. Then the die off would start again.

Please know that this is speculation on my part, but I have had a berry of babies get to a certain size and die off. Then it hit me that it was the only tank in the house that didn't have air stones. Since I put the air stones in the tank I haven't had any more problems with them.

One other thing, I wouldn't use quartz since quite often metals (gold, silver and many others) are found in it. Crayfish and metal don't get along well at all.

My tanks are very succesfull with dwarf cajuns because i go against the conventional wisdom used for shrimp. These are crayfish and are hapy with much worse conditions than shrimp. I over feed, have too many fast growing plants, and even nasties like planaria.

I use lots of plants like hornwort, and use an undergravel filter with pea gravel. I never vacuum. I keep loads of pond snails, apple snails and red rams with them.

Wood is something I never use.

The baby crays love having the gravel to hide & hunt in. My tank has loads of microfood for them. Lots of cyclops and seed shrimp. Who know what else? These guys live in swamps and ditches, not pristine pure water. Until my tanks got really aged, I had troubles keeping them alive. Now I have loads.

Next experiment id to use lots of that filter media that is little ceramic tubes. I think that willimprove the survival of the babies.

My water is super hard, something like 400-500 PPM.

Vera wrote:I don't know a lot about this species specifically, but I didn't see anything about air stones or anything to help with the gas exchange. Quite often crayfish will lay to their side die "from no apparent reason" when they can't get enough oxygen. It is usually in numbers at a time if there are more crayfish than the oxygen in the tank can support. After enough have died, there wouldn't be a lack of oxygen for a while, perhaps until more of the babies got to a larger size. Then the die off would start again.

Well adults were the first to die....but nonetheless you gave me an idea.....


Over the last couple of months the flow from my Whisper Power Filter has continued to slow.....It was like 3 constant trickles rather than the "wave" of water.....perhaps that would explain why the shrimp survived and the crayfish dwindled..... i would think this trickle would cause Oxygen to be more availible higher in the tank....the shrimp can swim better.....and the crayfish can only climb the plants to the halfway mark.... Crayfish swimming I wouldnt think would be very effective....burning all that energy for a gasp of more oxygenated water.....


I cleaned out the Whisper Power Filter and it is now a strong wave again....we will see how this works out......

How clean is the substrate? Part of the problem could be a buildup of debris polluting the bottom "layer" of the tank, where the crayfish can't escape the nasty effects of decaying organics. I recently lost the orange dwarfs in my 10 gallon cherry shrimp tank. When I stirred the gravel bed, gas bubbles popped up all over the place. Apparently MTS aren't effective for preventing that problem in gravel. I siphoned quite a lot of debris out of the gravel bed, and have been continuing to siphon it with weekly water changes.

With cajuns I've found that less is better. The combo of pea gravel, lots of plant and no vacuuming is doing plenty for mine. I don't know if I have some sort of "sweet spot" but I'm doing very little and I'm able to breed them like crazy.