Reproduction and maturity of kutum (Rutilus kutum) in Iranian waters of the Caspian Sea

To investigate spawning time, sexual maturity, and fecundity of kutum, this study was carried out in the Iranian waters of the Caspian Sea during February to April 2019. Samples were taken randomly from the catch composition of 119 beach seines in three provinces of Guilan, Mazandaran, and Golestan. The mean (± SD) fork length and total weight calculated 39.8±5.9 cm and 830.6±360.3 g, respectively. The sex ratio was 1:0.88 (M: F) that was significantly different from 1:1 ratio (p<0.05). Based on the frequency of different sexual maturity stages and the trend of gonadosomatic index (GSI), the peak of the spawning period was the second decade of April. The mean (± SD) absolute and relative fecundity were 45180±12239 and 47.5±8.6 eggs respectively. Absolute fecundity increased by increasing length, weight, and age and had positive and high correlations with these parameters. The length of maturity calculated 36.3 cm (fork length). The results show that the length of maturity and fecundity decreased in the last decade. Fishing pressure and high exploitation, as well as artificial reproduction and release of juveniles to regenerate the stocks of this species, which has caused genetic changes, are among the most important factors in reducing the length of sexual maturity and fecundity. It is recommended to review the fishing and exploitation regulations, to apply time, place, and instrumental restrictions and to provide suitable environmental conditions for natural reproduction and to reduce artificial reproduction and release.