question about raising fish for food in a system of interconnected ponds

First time poster here but long-time lurker. My dad and I are looking at permaculture to help improve our land and i was hoping someone could point us in the right direction when it comes to breeding fish.

I'm pretty new to fish but we have a system of 3 ponds that are interconnected through wetlands in hardiness zona 8a (in winters get temperatures as low as -15c).

The ponds were dug years ago by my father with the purpose of cleaning the - often eutrophic - water we take in from a small river. The wetlands and the ponds act as a natural purifying system so the last and lowest pond, where the water should be the cleanest, is used for swimming (it also serves as a microclimate for our veg garden). At the end of the system the water is returned to to the small river.

Now I'd like to stack another function and raise fish in the ponds for food. There are already grass carp on there but they are there for weed control, not for eating. I was thinking of breeding rainbow trout but I'm not sure how to approach that. Should I stick to one pond or do I use all 3? If I use all 3, how would that work?

Any help on resources or further reading would be much-appreciated!

By the way, the highest pond is about 150 square meters and 2 meters deep. The lowest pond is about 500 square meters and 3 meter deep. The middle one is somewhere between the 2 in terms of size.

8A is pretty warm for trout.  Catfish would seem to be a better match.

Rainbow trout need cold, well oxygenated water, and they can't spawn successfully in lake/pond environments.  If your pond's water temperatures are exceeding 20 C in the summer, and if the water source is eutrophic, rainbow trout may not be the best match.  Plus, they'd need to be re-stocked every year or two since they can't spawn.  

BUT...you could probably grow them out seasonally.  Stock fingerlings in the fall as water temperatures decline, let them grow through the winter, and either seine or catch them out of the ponds in late summer as water temperatures get high.  Here in the states, many fish and game agencies as well as private landowners stock ponds with rainbow trout for a fall/winter/early spring fishery.  

Good luck!

What type of fish live in the water source? The more edible types that are naturally occurring would probably be the best for propagation. Are the ponds set up for harvesting fish? If not, then cage culture may be the best way to go. To grow large numbers of fish, you'll need to provide at least some supplemental feed.