Diversity and abundance of fish in the Sefidroud River

The Sefidroud River is the largest river in the north of Iran and has a special importance in the survival of Caspian anadromous fish. In this study, the biodiversity and abundance of fish were investigated in eight points of the Sefidroud River and one point on the sea coast from March 2022 to January 2023. There were identified a total of 40 species of fish from various ecological groups; riverine (26 species), migratory (6 species), and estuarine-marine (8 species). The highest and the lowest number of species were observed in the mid-region of the river and the marine area with 21 and 17 species, respectively. The spatial ecological niche was observed for some species such as three Gobiidae species Caspian goby (Neogobius caspius), Caucasian dwarf goby (Knipowitschia caucasica), and Iranian Goby (Ponticola iranicus) occupied the sea coast, the estuary, and the upstream area, respectively. Mugilidae species were also seen up to 10 km from the sea. The eggs and larvae of anadromous fish were observed in the highest station. Kutum (Rutilus frisii) and Danube bleak (Alburnus chalcoides) fry fish had the highest abundance among the identified species of with 222 and 92 number/200m2, respectively. Bream (Vimba persa), Leaping mullet (Chelon saliens), European bitterling (Rhodeus amarus), Sanias spined loach (Cobitis saniae), North Caucasian bleak (Alburnus hohenackeri) had moderate frequency between 27 to 59 number/200m2 and the abundant of other species was low between 0.014 to19 number/200m2. The lowest Shannon's diversity index was in the furthest distance from the Caspian with value 1.03, while the highest value, with significantly difference p<0.05, was observed in 5 km to the sea with value 1.6  Also, the highest and lowest values ​​of the index were observed in November 2022 and January 2023, respectively.