Biological characteristics of autumn and spring runs of Caspiomyzon wagneri into the Shirood River, Iran

Various biological characteristics were compared between autumn and spring runs of Caspiomyzon wagneri migrating into the Shirood River, in an attempt to determine whether these were reproductively isolated. Two spawning runs of the same lamprey species in a single river are apparently unique to the Shirood. The autumn sample collected between 21 October and 1 November 2009 comprised 15 adults and the spring sample collected between 22 March and 18 April 2009 comprised 38 adults. While spawning was not witnessed, the significantly shorter mean total length of at least 40 cm in both males and females, and the significantly higher gonadosomatic index in females of the autumn run versus the spring run suggest that the former is closer to spawning than the latter. If one assumes a single spawning population per year in the river, the report by Nazari and Abdoli (2010) of recently spent individuals of Caspian lamprey collected in the Shirood River during April, would therefore imply that the spawning period is remarkably protracted. In order to test this hypothesis, the spawning sites need to be searched for higher upstream over the entire year, particularly in areas where suitable spawning substrate of gravel and sand occurs.