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I got 2 O. virilis from a stream about 2 weeks ago. Here's my notes and setup for them:

They are in a 10g tank, no heater, but with bubbler and HOB filter, sandy bottom. pH about 8.0, hardness about 800, nitrate and nitrite almost zero. Temps around 78-80F, sometimes up to 82F. I know crays like cooler waters but these come from a shallow stream. Average depth is 4", so the water there must be 84 or higher during the day.

I have a roughly flat rock (from pet store) leaning against the side of the tank for a cave. There are also 2 blacknose dace (minnows) in the tank plus 2 ghost shrimp. A 3" and 1" O. virilis are also there. I also have 2 fake plants for cover.

I feed them shrimp pellets every day. If they can, they run right out and grab one, then run back to their cave to eat it. Lately I've given them string algae to eat and they love it. (Their stream has lots of string algae and I've read on the net they appear in streams where ever there is string algae, so it must be a primary food source.)

2 days ago I gave them 3 blobs of algae, each bigger than a golf ball. The next day it was completely gone. The next day I did the same thing, they ate all of it during the night. This algae floats so the first time I weighed it down with a shell. The second, I pressed part of it into the sand bottom. Both things worked.

I used to have a 5" crayfish (unsure of which species, possibly Rusty crayfish) but he escaped after about a week. Apparently covering all holes in the tank top is not enough, you should weight them if you have larger crays also. He probably escaped because the fake plants were near the pump inlet so he climbed the plant, then the pump, then out. I moved the plants after that.

The shrimp and crays seem peaceful with each other. They are frequently within reach of each other and I've never seen a cray grab for a shrimp yet. But this could mean the crays are just well fed.

For caves, I did cover some 4" PVC with aquarium sealant and sand, but took it out, thought it might have to do with killing all my ghost shrimp. It seems though that my pH was the problem with the shrimp, as most pet stores keep their tanks at 7.0, my tank was at 8.0 and that's 100 times difference between 7 and 8 pH!

I also have a 4" bubbler bar. I have found the 1" cray under that several times hiding. I also lean large scallop shells against things, and have found the 1" cray under that too.

Anyway, at the stream I caught 22 crayfish. 20 appeared to be O. virilis, with 2 being possibly rustys. Only 4 were 4" or larger, so most were this year's young?

You have to keep in mind that even with the stream being so shallow it is constantly being replaced by fresh colder water from deeper parts. Not sure where you live but when I was collecting crays on a trip to florida a few years back even during the hottest weeks the water in shallow creeks & streams wasn't over 74F & those are crays that can take the heat.

O. Virilis will do best under 72F anything over that and it actually increases the crays metabolism to the point that they start having bad molts & their life span is shortened big time. Also a good rule of thumb for crayfish is to have at least 10gal per cray.

Stream depth of this stream is shallow for miles around, about 1-2". It's a city stream that runs through very built up subdivisions. The city commission just happened to keep the stream instead of filling it in. So the stream goes underground sometimes, in cement tubes.

I'll keep that in mind about the temperature. I should go check the temp at the stream today, just to see what it is. It's not real cool, I'm pretty sure. And where the crayfish live is a pool which is a deeper part of the stream. It is 10" max depth.

I measured stream temp. Keep in mind the air temperature has been 88-95F for several weeks. Anyway, stream temp in bottom of wide area (about 10" deep) was 76F. Tank hovers around 78F and the crayfish appear ok, though they both have molted twice in 4 weeks. I have been feeding them lots though. Just enough so they don't have any left over.

Per another note I wrote in another thread, my crayfish were found in a dark colored stream and they were dark. I put them in a tank with light colored sand, and after about 4 molts each, they are now light colored.

Also if you use intense lighting & light substrate over time you can get most species to turn blueish.