Dictionary of Ichthyology  

beaver fish tail = the 17th century concept that the tail of a beaver was fish-like and therefore beavers were fish and edible on Roman Catholic meat fasting days. First raised by the Bishop of Québec. See also beaver tail.

Beaver fish tail, Platearius, Livre des simples médecines, ca 1480, Paris from Wikimedia Commons: http://commons.wikimedia.org/wiki/File:Beaver_fish_tail.jpg.....more

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