Oh Way, I'm sorry
Guinness is made with a substance called isinglass, which is derived from fish's swim bladders.
From Wiki: "Isinglass finings are widely used as a processing aid in the British brewing industry to accelerate the fining, or clarification, of beer. They are used particularly in the production of cask-conditioned beers, known as real ale, although there are a few cask ales available which are not fined using isinglass. The finings flocculate the live yeast in the beer into a jelly-like mass, which settles to the bottom of the cask. Left to itself, beer will clear naturally; however, the use of isinglass finings accelerates the process. Isinglass is sometimes used with an auxiliary fining, which further accelerates the process of sedimentation... Although very little isinglass remains in the beer when it is drunk, many vegetarians[who?] consider beers (such as Guinness and almost all real ales), which are processed with these finings, to be unsuitable for vegetarian diets (although acceptable for pescetarians)."
From Wiki: "Isinglass finings are widely used as a processing aid in the British brewing industry to accelerate the fining, or clarification, of beer. They are used particularly in the production of cask-conditioned beers, known as real ale, although there are a few cask ales available which are not fined using isinglass. The finings flocculate the live yeast in the beer into a jelly-like mass, which settles to the bottom of the cask. Left to itself, beer will clear naturally; however, the use of isinglass finings accelerates the process. Isinglass is sometimes used with an auxiliary fining, which further accelerates the process of sedimentation... Although very little isinglass remains in the beer when it is drunk, many vegetarians[who?] consider beers (such as Guinness and almost all real ales), which are processed with these finings, to be unsuitable for vegetarian diets (although acceptable for pescetarians)."