If you are interested I built a FHM "condo" for my RES/SMB pond to give the FHM something to spaqn on. It was not in a cage but instead staked to the bank of the pond. But it might give you some ideas.
Did it work? Darned if I know. I got the idea from some youtube videos on FHM or Rosie Reds spawning in aquariums. Several people were using PVC pipe as a substrate for them. So I got the idea of making a colony of PVC pipes. I tried to turn the pipes different directions to give the couples the most privacy and minimize competition. The holes drilled in the pipes were for water flow and good aereation (at least my idea of it).
Scroll down the page to where the title includes the words "some FHM substrate. 2/3 the way down the page. The installation of it in the pond is further down that same page.
https://forums.pondboss.com/ubbthreads.php?ubb=showflat&Number=459159&page=6I like that "condo." I put together a couple of pallet stacks out there before my pond filled up but now wish I would have put more. I also put a few brush piles of mostly cedar.
I think for the cage I could go with a combo of pipes between layers of wood. My thought right now is that the cage will be about 4ft square. I want it small enough to move around and service as needed. I probably won't have a lot of room as I will likely leave a gap in the middle for a minnow dip net if I want to try to take some out without first removing the structure.
If my cage is 4 ft. square and either 2, 3 or 4 ft. deep. I wonder how many minnows I should put in it? I wonder what the limit will be such that they become a constant menace to all who are trying to guard eggs. Will they destroy one another's nests? I'd like to stuff in as many as possible.
I will be making another tester cage to keep in a large pet or baby pool to see what kind of production I can get expect.
