if the fish are small enough to go thru eggcrate, you can get sheets of plastic cross stitch canvas. tie it against the eggcrate with fishing line. it comes in a variety hole sizes. buy anywhere they sell yarn craft supplies.
Thanks guys, I looked at screans but Idk if its safe to use so im just going use plexiglass. Like I said the holes are too big on the eggcrate. But thanks agen!