Think about it:You donate 1 creature, but Blathers sometimes has multiple of the creature. Did he just catch them himself? Possibly, but take into account that Blathers is terrified of bugs. Thus, he most be cloning them. Have you ever seen Blathers leave the museum? No? He must eat the fish and sea creatures. But what if the cloning machine broke? Well, all the fish and sea creatures would be gone, except for the ones in the bug side. And lets just say that if somebody came into the museum, there would be a new "fossil" in the exhibit.