There is a huge variety depending on your end goal. First, they pretty much need to be freshwater unless you are growing kelp or saltwater algae. Then you have to decide if you want to eat them. For food fish – stay with vegetarians or detritus eaters. Its better for the food chain. Tilapia and catfish are all time favorites. Just know the tilapia are pickier about warm water. You can also grow freshwater prawns and crayfish – try the Australian red claw. They grow fast, breed well and are less aggressive than many crayfish. They taste good too! If you are keeping fish because you love looking at them and all the wonderful produce from aquaponics try koi or any of a variety ornamental tropical fish such as guppies, tetras, swordtails, mollies, and others.