Population dynamics of Spirlin (Alburnoides sp.) (Pisces: Cyprinidae) at the Up and Down stream of Shahid Rajaii dam of Tajan River

This study was designed to evaluate population dynamic in the Tajan river and investigation Shahid-Rajaei dam effects upon Alburnoides sp.. A total 621 fish specimens during 9 month were collected by electeroshocker set that 508 individual related to up stream station and 113 individual related to down stream station. The mean fork length and weight of this species in upstream was 49.11± 11.95 cm, 3.29 ±2.69 gr and in downstream was 52.94± 11.93 cm, 3. 92 ±2.96 gr, respectively. Univariate analysis (One-Way ANOVA) of length between two stations showed significant differences while weight and condition factor only in male showed significant differences (P≤0.05). The age of the female samples in upstream of the dam in 4 class ranged from 0+ to 3+ years while other (male in upstream, male and female in downstream) samples in 3 class ranged from 0+ to 2+ years. Sex rate of male: female in up- and down stream were 57.9:42.1 and 61.3:38.7, respectively that shown female were dominant in two stations. We observed an isometric growth pattern in males caught in downstream and positive allometric in the rest of fishes andValue of condition factor in both stations were above of 2.