Bullhead, when I built my fish cage I filled the top pipes with foam and drilled all the other pipes so they would fill and drain water easily. I zip tied some foam noodles to the top to give it some extra floatation. The trap door is plywood so that it gives them some shade, and I also made a divider if I choose to separate any fish. I built my cage similar to Cecil's cause he has lots of experience raising fish in cages, but that's not to say that the other designs aren't just as good.
