Prepare an aquarium ahead of time for the freshwater crayfish. Use a 1-by-2-foot-long tank for each pair. Put a layer of gravel on the bottom. Arrange rocks, tiles, flowerpots or decorative objects to create nooks and crannies for hiding places. Aerate the water with a fish-tank bubbler, as crayfish breathe through gills. Keep the pH at neutral or slightly alkaline, in the range of 7.0 to 8.5. Test the pH with litmus paper. Add baking soda or vinegar to adjust the pH. Use a thermometer and fish tank water heater with a thermostat to maintain a water temperature of 65 to 80 degrees Fahrenheit for optimum growth.