Dsea,
Some pictures would help but if your fish box is similar to mine (I have a different boat) it used to have a macerator pump and hose which pushed the water and ground contents overboard through a through-hull fitting at the stern. However, on my boat the PO removed this pump and my box now drains directly into the bilge area. I just use for storage but I have two large fish boxes in the front.
Without knowing what lies beyond your screened drain hole, and to directly answer your question... I would refrain from both removing the screen and/or putting fish in there if it drains into the bilge area. That is a sure fire way to ensure your below deck area will seriously stink due to the left over water and other chit that comes out of a fish after they are caught.
If you are dead set on putting live or dead fish in there I would restore it to what was the likely the factory setup where a macerator pump and hose disposes of the waste and water from the box. If kept screened you could likely get away with a non-macerator pump as the screen would keep the particulate from the pump. But either way I would want the fishy chit pumped out.
Just a couple thoughts.. I think the group will need more info to give you a definitive recommendation. Pictures are always a plus.. Good luck.
B
