Dictionary of Ichthyology  

juglone = a piscicide (5-hydroxynaphthoquinone) used in Japan and made from the roots and fruits of Juglans mandshurica (Juglancaceae). Other piscicidal plant chemicals include callicarpone, huratoxin, ichthyothereol, inophyllolide, justicidin, maingayic acid, rotenone, and vibsanine, all q.v.
Female flower from Wikimedia Commons: http://commons.wikimedia.org/wiki/File:Juglans
_mandshurica_var._sieboldiana_female.JPG..... more

           Canadian Museum of Nature
         www.briancoad.com