Upon the fractionation guided by piscicidal activity using the Medaka
(Oryzias latipes), three piscicidal substances were isolated from the
root of Inula nervosa, and were characterized as thymol and its deriva
tives based on the spectral analyses including 2D nmr techniques. A ne
w piscicide, named inulavosin, was a thymol dimer with a new heterocyc
lic skeleton.