Isinglass is a fining - when added to beer it helps the beer clarify - and it's a form of collagen derived from fish swim bladders.
Given that this is an animal-derived product, do breweries have to declare this on the packaging?
In 2003, the EC discussed requiring labeling for Isinglass as a potential food allergen.
The brewers in the EC successfully argued that it was part of the processing and not an additive and thus did not require labeling.
Isinglass finings are a tried and tested method of clarifying beer and so it came as a great relief to traditional cask ale brewers when the EC, last year, introduced an amendment to the 2003 labelling directive. The brewing industry successfully argued that as a processing aid, not an ingredient that would be consumed, and with a long history of use with no recorded incidents of an allergic reaction, there was a good case for isinglass to be exempt from the directive.
At least in the United States, there is no requirement for ingredients to be listed on bottles/packaging. While foods are required to list ingredients, this is because they are regulated by the Food and Drug Administration (FDA). Beer and other alcohol, on the other hand, are regulated by the Treasury Department which has no such ingredient listing requirements. So, Isinglass would need no special ingredient listing.
Some of the ingredients found in many American beers that might surprise you include:
There was a law enacted in Germany in the 1400's concerning purity of beer, known as Reinheitsgebot. This has been adapted and changed slightly since then, and was adapted in the 1950's into a taxation law that also addressed purity (Biersteuergesetz). The taxation law was relaxed in the late 1980's, and allowed any ingredients allowed in food to be allowed in beer. This only applies to imported beers, however, as German breweries still have to abide by the purity restrictions.
Food Standards Australia New Zealand approved an amendment to the code in March 2009, providing an exemption to mandatory labelling requirements for the use of isinglass in beer and wine.
Clause 4 of Standard 1.2.3 deals with ingredients that trigger a mandatory declaration. The "fish products" line of the table of covered ingredients was amended to read
Fish and fish products, except for isinglass derived from swim bladders and used as a clarifying agent in beer and wine
The report from FSANZ also included a survey of international laws regarding isinglass. In addition to the USA and EU that have been covered by other questions, it mentions:
Health Canada amended its food labelling requirements in September 2004 such that fining agents derived from fish, milk and egg, used during the manufacture of standardised alcoholic beverages, would be exempt from the allergen labelling requirements.
In Japan, Fish is not included on the list of allergens requiring mandatory labelling, with only certain fish species being recommended for labelling. However, alcohol beverages and related products are not subject to the allergen labelling requirements, so wouldn't be covered anyway.
The Codex Alimentarius General Standard for the Labelling of Pre-packaged Foods (Codex Stan 1-1985) requires the declaration of fish products used as ingredients or food additive, and makes no mention of an exemption for isinglass. In countries that have adopted this standard without making any modifications and apply it to alcoholic beverages, use of isinglass would presumably have to be declared.
I think what you are trying to get at is should it be disclosed for people who might be ideologically or otherwise opposed to consuming or using animal products. If that is the case then I think you should disclose on your packaging.
It does should like more of a filtering agent than an ingredient though, so like passing something through a charcoal filter. You don't see charcoal as an ingredient.