The population dynamic of the Chub Squalius cephalus (Linnaeus, 1758) in the Shahid Rajai Dam Lake (Sari, Iran)

To study of the some parameters of population dynamics of S. cephalus in reservoir of Shahid Rajaii dam, 591 specimens were caught by gill nets during six sampling times at 3 stations in four seasons. The most frequent catch was for season of autumn (303) and the lowest was captured in winter (43). Specimens caught for both sexes were in 6 age groups 0+ to 5+ years that, 2-year-olds were prevailing in both sexes. The sex ratio of males to females were 1:1.06, that, with not were significantly different (p>0.05, χ2=0.61). Specimens ranged from 102 to 265 mm in length and 11.59 to 241.86 gr in weight. In overall, the length and weight of the females was higher than males (p<0.05). The weight-length relationship was estimated as for females, for males, and  for the population, having a positive allometric growth in all considered groups. The Von Bertalanffy growth equations for males and females were calculated respectively Lt=27.04(1-e-0.23(t+2.03)) and  Lt=31.4(1-e-0.22(t+1.31)) that the infinity length in females was more than males. The condition factor almost was equal in both sexes (p>0.05) but was significantly different in age groups from ages 0+ to 3+ between sexes. The maximum of gonadosomatic index for both sexes was observed. The average absolute and relative fecundity were 4478.2±75.6 and 54.1±65.6 respectively. The average of female egg diameter was 0.86 ±0.12 mm in this study. Checking of relative length of the gut (RLG) showed a tendency to carnivorous feeding and Vacuity Index (CV) showed that males were relatively edacious and females were edacious. Based on Index of Fullness (IF) in both sexes and different ages, feeding conditions of this species is not appropriate. After 15 years of the formation of the lake, the view of many dynamic parameters of S. cephalus in reservoir better than river.