KennyTheShark ... well, this probably happens a lot among aquarists. But this is how we learn, through experiences. It's OK, please don't be too sad though. The chances of the fish recovering are probably small, but then you never know, so keep your head up
Yes, next time when you have a fish that is small enough to fit through the filter intake tube, you can get a breeding net (I think that's what you referred to). You put the breeding net inside your tank, and then put the fish inside the net. It's a good thing since it allows a good water flow but still doesn't let the fish out.
Another thing you could do instead of buying a breeding net or instead of buying a new sponge filter, I suppose, it to wrap the intake tube with a stocking (sheer stockings that women wear). This won't let the fish pass through the holes in the intake tube but the water will still be filtered.
OK, enough of my babble. Hope the fish will be OK! Good luck!