Cobitis taenia is one of the index samples and as apart of benthal fishes in the waters southern costal of Caspian Sea. In total 410 Cobitis taenia were caught. Sampling has been done by electroshocker 300 V, monthly and during one year since Oct. 2008 up to Sept. 2009 According to condition of sampling, the sum of two stations sampled monthly between 16 to 50 and has been distinguished randomly at two Kaselian and Tajoon stations of stuaries of Kazar sea.
Average egg diameter of fish by Measured in the Loop was highest in April and this trend continued until May, and the average diameter in April was 36.20 Micron with SD 6.52. Investigation showed that the gonads of these fishes at sexual maturity occurs in April. Average percentage of sexual maturity index (GSI) 1.04%, respectively with SD 0.42. Average liver weight index (HSI) equal to 0.156  with SD 0.009 was calculated, so that the peak time of sexual maturity, we see a reduction in liver weight. Total length of fish at the time of sexual maturity (Lm50), with an average 67.44 mm, SD 11.17 and average weight 2.33 g and SD 0.64 was calculated. The HSI (liver weight) in spring than in other months showed a significant reduction in the loss is inversely proportional to the amount of GSI in this chapter.