Just to confirm what others have said, we had a syno in our tank for a while. We were told by one fishmonger, if you will at a LFS nearby that they were compatible w/ everything and that there would be no problems.
Well, what a liar Mom turned out to be. We started to notice neons disappearing 1 by 1, w/o a trace. not even a little bit of any bodies. When we started dealing w/ our "trustworthy" (read as: in it for the love of the fish and not $$$) he told us that, as others said, if it fits in the syno's mouth, it's an hors d'ourve. We quickly relocated said syno to another tank and there has been no problem since. Actually, the syno in question wasn't even fully grown yet, was only 3-4 inches in length. Beware Britfish...beware as there should be no further murders in the area.