a comparison of fecundity of sand goby(neogobius pallasi) in babolroud and tajan rivers in mazandaran province

considering its gobiidea and feeding fish sturgeon caspian sea highest main and the need to fecundity this fish, this study was done in babolroud and tajan rivers in mazandaran. in order to conduct the study, 197 sand goby we were caught using an electros choker machine (v300-200) in the spring of 1390 ,which was the spawning season, at the tajan river (sari) and babolrood (babol). 103 fish which had not spawned were analyzed. according to the results of the study, the highest average standard length of fish 96.99 ± 1.43, body weight 25.01±9.83 g , gonad weight 1.39 ± 1.03 g and absolute fecundity 952.19 ± 8.49 number of egg fish  belonged to sand goby  in tjan and the least average of  standard length 74.12 ± 1.38 mm, weight 11.03 ± 7.23 g, gonad weight 0.61 ± 0.27 g and 684.53 ± 2.24 numbers of egg  were reported for sand goby  on the babolrod river. the maximum and minimum averages of relative fecundity were respectively 76.96 ± 3.65 and 39.39 ± 2.65 sand goby in  babolroud and tajan rivers. the highest mean of egg diameter 1.11 ± 0.28 mm gonad somatic index 7.44 ± 5.05% belonged to  sand goby  in  babolroud  river and the  lowest, percentages were respectively 1.06 ± 0.28 mm and 5.66 ± 3.10 for the sand goby in  babolroud. according to the measured biometrics and fecundity factors of the rivers, there is no significant difference between the two (p> 0.05).