there isnt a need to winter fish indoors. there are just some things that need to be addressed when building your pond. if you live in a climate with harsh winters, you just need to make your pond deep enough so it doesnt freeze solid in the winters. a pond can ice over, as long as there is a hole in the ice for oxygen exchange. they make small heaters for this which keep just a hole about the size of a basket ball oopen in the ice. koin and goldfish will go into a hibernation type of mode when the water temperature drop to around 40 deg f. stop feeding when the water temp hits around 45 and turn off you pumps. this will allow the deeper parts of your ponds retain heat, and the lawer of ice also acts as insulation.