well just a word of thought I have 1 crayfish myself in my 40G freshwater and he has gotten bigger since I first got him 2 months ago and believe me if you have one just remember the risk your taking I would say keep one with fast moving fish and you'll be fine the one I got has not given any trouble to my pleco since he is a little bigger than him and as far as my shrimp well their smart and quick. I did have one small figure 8 puffer and he only lasted 1 week until my cray got him so just be careful.