Morphometric analysis of olfactory organ and telencephalon in maturing and mature migrants of Caspian lamprey (Caspiomyzon wagneri, Kessler 1870)

This study was conducted to provide a detailed information about changes of the olfactory organ and telencephalon morphology in spring and fall spawning run maturing and mature Caspian lamprey, Caspiomyzon wagneri, in the Shirud River, Sothern Caspian Sea basin, Iran. A total of 71 maturing and mature fish were collected during their spawning migration. The results showed that the thickness of the olfactory epithelium and the density of ciliated olfactory receptor cells (ORC) were lower in mature migrants. In addition, the nasal cavity, relative weight of olfactory organ and relative telecephalon area in mature migrants were larger indicating its more sensitivity to external queues. Based on the results, the olfactory organ and telencephalon of maturing migrants of Caspian lamprey have not developed completely and needs a period of rest in the river to its full development for spawning.