عنوان مقاله [English]
نویسندگان [English]چکیده [English]
A total of 4292 fish samples were caught. Sampling was carried out at 3 stations monthly, using a beach seine with 20 meter in length and 5 mm mesh size from node to adjacent node. The purpose of this research was to investigate the status of fish in the year of sampling in 1994 and compare it in 2014. A total of 9 families, 16 genera and 20 species were identified. The most species diversity was obtained from the family of Cyprinidae and Gobiidae with 6 and 5 species, respectively. Based on the results, the Shannon index ranged from 0.924 to 1.3622 and the Simpson index ranged from 1.893 to 3.158, the Margalf index ranged from 1.258 to 2.262 and the Pillow index varied from 0.341 to 0.619. This could be due to the ecological conditions of the area, the presence of canals, vegetation and proper water quality. There was a significant difference between the variability indices at different stations (p<0.05). Also, there is a significant difference in fish length and weight at different stations (p<0.05). The results showed that the Atherinidae with 48.9% and Cyprinidae with 36.94% were the most frequent. This could be due to the ecological origin of these species in the area, having shallow water, accessible food and as a natural pasture in the south-east of the Caspian Sea. Conclusion, the decrease in the coefficient of variation of 19.3% of species has occurred over two decades, which can be attributed to the decrease in Gorgan Bay water level and its change on the biological groups in recent years.