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Hello! I'm a long-term lurker/first time poster so please forgive me if I am posting this in the wrong place. I have had a crayfish (I believe to be a dwarf) for a little over two months. It was originally sold to me from my LFS as a "dwarf blue lobster" I believe it is possibly a Cajun dwarf, but I'm not sure. It hasn't grown much in the time that I've had it although it has molted at least once. About a month ago I added a cpo to the tank and although the two have made attempts to mate with eachother ive yet to see any eggs/offspring. Tonight I added two more cpos which were gifted to me. I currently have the 4 Crays in a heavily planted, well established 10 gallon tank with a couple of rabbit snails. The cpos all appear to be a little larger than the other guy, but I would really like to know what he actually is. I've read that cpo and Cajun dwarfs are capable of interbreeding and lord knows these guys have tried. (I catch them "mating" fairly often.) I recently saw a post on another forum where someone was sold marbled Crays (self cloning) as Cajun dwarfs and it has me worried about my random guy. He isn't really "blue" at all. I haven't had any problems with any of my Crays eating my plants or messing with eachother (other than their attempts to mate) and I feel fairly certain that my "blue" guy is too small/not growing fast enough to be a marbled. I would just really love to know what it actually is. I'm sorry for the length/wordiness of this post. The cray in question is roughly the same length of a nickles diameter (see my poor quality photos). Thank you all in advance for any advice/info you can provide, I greatly appreciate! I love the little guy/gal regardless of what it is, I just want to make sure I'm not putting it or any of my other lil guys in danger.
 

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Kind of hard to tell the color from your pics, but it is most likely a Cambarellus crayfish if it stays small.

There is Cambarellus diminutus, common name blue mini crayfish. From descriptions I have read, they stay smaller than CPO and adults are only the size of dwarf shrimp (Neocaridina/Red Cherry Shrimp).
Sort of doubt you have that one though because it is pretty rare and yours already looks possibly too large for it to be that species, so take a look at the other Cambarellus species (dwarf crayfish) and see what matches.
Note that I have read some reports of the colors varying depending on pH.

CPO's are Cambarellus patzcuarensis, still the same genus so it's possible they may crossbreed.

Marmorkrebs have the common name, marbled self-cloning crayfish, but this genus is not a "dwarf" cray.
There are marbled self-cloning Cambarellus which are dwarfs though.
 

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I think it is shufeldtii or texanus. Either can take on a blue tinge, but the theory is that it's not the natural color of either, but results from a certain diet or a harmless fungus. You will also find some people that swear they are able to breed for blue but I was never able to. I kept texanus and gave them to a friend, who gave some back. When I gave them to him, they were brown and black, when I got them back, they were bluish. They eventually faded back to brown/black. I wouldn't be surprised that they can breed with CPO, but in my experience CPO can be a little more aggressive, so I'd watch carefully. Overall, both texanus and CPOs were pretty peaceful for me as long as they had places to hide.

The stripes you see in some of the pictures tended to appear as the crays matured, if they were going to. Not all of my crays seemed to get them.
 

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Quite a few threads out there that talk about the color changes. So far, doesn't seem anyone has came up with a indefinite answer, but there is speculation, lower pH seems to be the most noted for bluer coloration. Some hint toward temperature or dissolved oxygen levels. Some say gender colors, etc. Maybe it's stress related? Hardness?

VIDEO of DWARF BLUE CRAYS - Crays and Other Inverts - The Shrimp Spot
Blue Mini Diminutus Crayfish - Crays and Other Inverts - The Shrimp Spot
Mini Blue Diminutus **SALE** SOLD OUT - The Marketplace - The Shrimp Spot
 

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Quite a few threads out there that talk about the color changes. So far, doesn't seem anyone has came up with a indefinite answer, but there is speculation, lower pH seems to be the most noted for bluer coloration. Some hint toward temperature or dissolved oxygen levels. Some say gender colors, etc. Maybe it's stress related? Hardness?
Just about any of those could be true of my friend's tank, except for maybe temperature (I don't think either one of us heated our tanks with crays and our temps are probably pretty consistent). My water is very hard with a high pH, and he probably uses some kind of RO system. I did not see a difference in blue color with gender, but it did seem that the females in my tank were darker, with some almost black, while males were a lighter brown. I can see where one might show off the blue better.

He confirmed that they were a bluish color in his tanks. It might be an interesting experiment to try different things.
 

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Looks like dims or texanus to me. The blue for me is ph based. I keep them in pretty much any tank as they are harmless to fish and plants and dont dig like most crays. In my high tech tanks where i keep the water around ph 6.0-6.2, they turn "blueish" (not really blue IMO), and when i move the same crays to std ph 7+ tanks they revert to various shades of brown. Diet is the same cheap fish food pellets i feed the fish so its not diet or temp in my case. Self clones are darker brown with spots.
 
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