Dictionary of Ichthyology  

polycyclic aromatic hydrocarbons = chemicals found in fish products as environmental contaminants, usually at low concentrations, much higher where there is contamination from petroleum and petroleum products. Found in smoked fish at 10 times or more than unsmoked fish. Some PAHs are carcinogenic.

Clockwise from top left, the molecules are: benz[e]acephenanthrylene, pyrene and dibenz[a,h]anthracene from Wikimedia Commons: http://commons.wikimedia.org/wiki/File:Polycyclic_Aromatic_Hydrocarbons.png

Canadian Museum of Nature