The biggest expense in raising my tilapia is the electricity to heat the water the fish live in. If the water gets down to 65 degrees the fish will die and they grow fastest when it is up around 80 degrees. I have a hot water element plumbed into the side of the IBC tank that the fish are in with a thermostat that allows me to keep the water at any temperature I want. Today I built me a water heater. It is a bunch of 2 foot copper tubes that I soldered elbows on and connected them into a grid that will sit on top of my wood stove. I have Pex connectors on the end of the copper and I am going to dig a ditch out to my greenhouse, lay some insulation in the ditch, and run the Pex line out to my greenhouse. It will be interesting to see how much it will heat the water up. I might have to much heat gain and have to put in a second tank, and raise some more fish. I have about 300 fish now with most of them being little baby fish that my Momma fish have had. In about another month I should have my second greenhouse done, and then I will have room for 6 300 gallons IBC tanks each which I can raise a 100 fish in. I will also have 12 3X8 grow beds and be able to grow a ton of vegetables. The water from the fish tank goes into the grow beds that are full of 3/4 pee gravel. The water is cleaned going through the gravel and goes back into the fish tank and the plants grow in the gravel like crazy with all the fish poop and warm water and grow lights. Just call me farmer Duke.