Study on the gastrointestinal tract characteristics and biological indicators of Caspian Lamprey Caspiomyzon wagneri (Kessler, 1870) migrants in the Shirud River, Mazandaran province

The aim of this study was to evaluate the gastrointestinal tract and biological indices during spawning migration in spring and fall of 2014. Sixty fishes were caught from Shirud River (Tonekabon, Mazandaran province, Southern Caspian Sea). In this study, Caspian lamprey (C. wagneri) was studied in terms of the biological indices including total length, body weight, intestinal length, and the weight of visceral, liver, intestines and ovaries. The fishes were divided into two groups of “mature” and “maturing” groups. The results of appearance observations showed that there was no specific stomach and esophagus, and its digestive tract only consisted of a straight and narrow intestine. In the most migrant fishes, intestine were empty and no significant differences were observed in dry weight of their intestine among all groups. In comparison of the total intestine length, relative intestine length (RLG) and visceral index (VSI), there were no significant differences among all experimental groups in different sex, seasons and maturation stage. Also, in comparison of Hepatosomatic index (HSI), there was significant difference between maturing and mature females in fall, whereas no significant differences were observed among other groups.