Yes, Guinness has traces, albeit very faint traces, of isinglass, an aspect of an air-bladder that provides fish with buoyancy. The isinglass is a gelatinous substance that attracts and removes dead yeast and other particles in the beer, helping to clarify it. It is removed before bottling, but remaining traces of it mean that the beer cannot be labeled as vegetarian. This technique has been used by Guinness since at least the 19th century, but probably longer than that. The Smithsonian’s site, in response to the announcement, has documented how the process works.