That is not a good idea since lobster require some care, and the water in your aquarium should be properly “cycled” prior to any Crayfish being introduced.
here is some info I found on Crayfish which ALL animals that are called freshwater lobsters really are.
Housing:
A ten gallon aquarium with a filter and a tight fitting top so as to prevent escape is great for one Crayfish. They are perhaps one of the best escape artists in the world. crays can jump out of the water like a fish and out of the aquarium on occasion given the opportunity.
Cray fish do best in water kept at 65 – 75 degrees Fahrenheit (18 – 24 Celsius). If your water temperatures should get higher than the recommended temps it is really not a problem unless they exceed the mid 80’s. Commercial raisers routinely keep their Crayfish at 82F/28C to speed up their metabolic rate which of course speeds up growth and aging.
Crayfish require a water ph of 7.2 – 8.4. A ph any lower than 7.0 is acidic and can actually leach the calcium out of their exoskeleton, any higher than 8.4 and it can become difficult for your cray to get enough oxygen.
Feeding Your Crayfish
Crayfish are opportunistic omnivores which means that they will eat almost anything they can get their pincers on. In the wild they feed on aquatic plants, algae, rotting vegetation that falls into the water, snails, fish, and decomposing mammals that die in or near the water.
In captivity the important thing is not to over feed which causes pollution in the aquarium.
Crayfish in the aquarium do well on most standard fish foods that sink. For baby crayfish I use fish food flakes made for Goldfish. For adult crays I use sinking shrimp pellets intended for general fish use.
The amount fed is quite small but you must keep in mind that the animal you are feeding is also quite small. For baby crays one large flake of food finely crushed twice a day is plenty. You do not have to worry about getting the particles exactly where the cray is setting since it will smell the food in the water and hunt it down. For adult Crayfish the same rule holds true, one pellet in the morning and one pellet in the evening is plenty and if you are using a large sized pellet one per day is enough.
If you attempt to keep more than one Crayfish in an aquarium you will need to be sure to drop meals in separate locations to reduce chance encounters.
You can also feed vegetative matter such as Water Lettuce, Water Hyacinth, Water Cress and Romaine lettuce but you will need to weigh vegetative matter down so it doesn't float to the surface out of the crays reach.
