Petromyzonol is a tetrahydroxy stearol which serves as the primary spawning pheromone in adult sea lamprey. It is produced in the bile of sea lamprey larvae from the bile acid precursor allocholic acid. While the adult sea lamprey is relatively insensitive to petromyzonol itself, the C-24 sulfate ester (petromyzonol sulfate) is a pheromone and a spawning chemoattractant which can be detected at very low concentrations by lamprey olfactory chemoreceptors. Petromyzonol, petromyzonol sulfate, and allocholic acid are all found in water samples from fresh water streams bearing larval lamprey populations.[1]
Reference:
[1]. Li, W., Sorensen, P.W., and Gallaher, D.D. The olfactory system of migratory adult sea lamprey (Petromyzon marinus) is specifically and acutely sensitive to unique bile acids released by conspecific larvae. Journal of General Physiology 105, 569-587 (1995).