If this is the electric blue crayfish, Procambarus alleni, they will get far too big for a 5 gallon. These ones can get pretty big, and they are pretty active too.
If you are referring to the blue brazos dwarf cray, then they would be a better fit. A 10 gallon would be preferable, but a 5 gallon is acceptable. They aren't as vibrant as the larger electric blue, many don't look incredibly blue at all but they are still attractive. You will need to provide a few places for it to hide, and it will need a tight fitting lid without gaps to avoid escape. Dwarf crays don't tend to harm plants either.
They should be fed invertebrate pellets, vegetables and frozen foods such as bloodworms and brine shrimp.
