if there is only one, get one of those 2 gallon hex "tanks" from petsmart. an airpump of filter is probabily needed. Don't fill the aquarium full of water or you will give the crayfish an easy escape um you can try using tap water and a conditioner but your best bet is to use pond water from the pond you got it from (unless its gross and icky) I know they eat fish babies; hmm it depends on how big this crawfish is. If he is a good size you can probabily feed him feeder fish (smallest ones) or some kind of pellets? It may not live that long so get upset if it dies