You've probably heard of both fish farms and hydroponics; put the two together and you have aquaponics. There is at least one guy currently selling a start up kit on-line for a bargain basement price, but if you look on YouTube you can probably work out how to begin your own home farm for next to nothing. The universal guru in this relatively new field appears to be American Nate Storey, so check him out. And there is at least one group of people combining aquaponics with solar power, which means that - in Kenya at least - this is a sure fire way of feeding the family for free, and heating the home. Not that they need much heat there.