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.
Male flower from Wikimedia Commons: http://upload.wikimedia.org/wikipedia/
commons/9/95/Juglans_mandshurica_var
._sieboldiana_male.JPG

           Canadian Museum of Nature
         www.briancoad.com