So, you've built your DIY spawning mops and now you have eggs. Congrats! But now you've got to protect your eggs, otherwise the bigger fish will eat your fry. You could put them in an aquarium in your house until they are big enough to go back into the pond. I prefer to keep the fry in the pond, so I built myself a fry hatchery to grow them out in. That way, I don't have to clean a separate tank.
Here's how to do it!
You'll need a bunch of fittings to form a rectangle or square frame from PVC. These are some parts I had sitting around, so that's what I used. Mine were 3/4" pipe.
You can build this any size that works for you, but try to build it shallow enough so that it does not sit on your pond floor (due to any crud that might be there)--you want it to float.
Start off by building two matching sized rectangle frames like this:
Now, you need to connect your frames together to form a 3-dimensional box. Here's a great hint: spray paint your frames black with plastic krylon paint, and you won't even see the hatchery in the water.
Well, here's my finished product. It didn't take long to do!
Now you've got to get some screen material from the home improvement store. Make sure to buy it so the holes are small enough that a tiny fry can't pass through it. If it's small enough to keep mosquitoes out, it's good enough for fry. I like to buy the pliable, plastic kind instead of the metal screening--but you can do either.
Using plastic zip-ties, begin strapping your screening to the pvc. Make sure to fold your screening properly all around so you don't have any holes that a little fish can slip through:
Clip off all the long strips from the zipties until they are all flush to your pipe:
That's it! You're done and you are ready to put it in your pond. When you see eggs on your spawning mops, just put the mops in the hatchery and get ready for baby growth!
This is my opinion. It is worth exactly what you paid for it.