Crayfish are another matter. Dwarf crays can be bred in a 55gal for a couple of pairs. You'll need lots of hiding places for the young. Most will be eaten but, some will survive. For a larger yield and for larger crays, You'll need several tanks and a grow-out vat/bin. A male can be introduced to a tank with several females. Once spawning is completed, remove the male. Once the females berry (display eggs in swimmerettes), place lone females in their own tank. After the eggs hatch the young will cling to the female for a time determined by species and temp. Once the larvae drop off, remove the female. Provide TONS of hiding spaces, throughout the water column, for the larvae. The fast growing young are more cannabalistic than their parents and larger larvae will eat their slower growing siblings. Then it's just lots of mixed animal and plant protein foods, lots of water changes, and calcium supplements to provide material for the carapaces of the developing young.