Age determination, growth indices and reproduction biology of Prussian carp, Carassius gibelio (Bloch, 1782) from four reservoirs in Golestan Province, Southeast Caspian Sea

This study aimed to determine age and growth indices of Prussian carp, Carassius gibelio collected a total of 942 specimens on a monthly basis from February through September 2015 in three dam lakes including Golestan, Boostan and Voshmgir and one reservoir named Alakoli from the Southeast Caspian Sea. The largest specimen was a female with 220 mm in total length (TL) and 139.787 g in weight from Voshmgir. The maximum condition factor of the fish increased markedly during late April- August in all areas. Growth pattern was positive allometric in females from Alakoli, while negative allometric in females from Golestan, Boostan and Voshmgir and also in males from Voshmgir. The isometric growth observed in males from Golestan and Boostan as well as from Alakoli. The growth parameters of von Bertalanffy fit to the mean observed total lengths-at-age for each sex separately were estimated as L∞= 378.09 mm, K= 0.12, t0= -0.35 for females, L∞= 309.38 mm, K= 0.17, t0= -0.02 for males, and as L∞= 355.74 mm, K= 0.13, t0= -0.35 for total population in Golestan; L∞= 299.06 mm, K= 0.18, t0= -0.10 for females, L∞= 574.17 mm, K= 0.07, t0= -1.04 for males, and as L∞= 338.43 mm, K= 0.15, t0= -0.34 for total population in Boostan; L∞= 296.37 mm, K= 0.20, t0= -0.20 for females, L∞= 186.23 mm, K= 0.51, t0= -0.42 for males, and as L∞= 302.94 mm, K= 0.19, t0= -0.18 for total population in Voshmgir; and L∞= 347.99 mm, K= 0.04, t0= -0.12 for females, L∞= 530.92 mm, K= 0.01, t0= -0.18 for males, and as L∞= 477.73 mm, K= 0.01, t0= -0.40 for total population in Alakoli. A prolonged spawning period was observed from April through August. Maximum egg diameter and absolute fecundity were 1.39 mm and 72865 oocytes in population inhabiting Voshmgir respectively.