Reproductive condition and ovarian atresia in the common kilka (Clupeonella cultriventris) from the Caspian Sea years after a dramatic outbreak of the comb jelly fish (Mnemiopsis leidyi)

Abstract

To assess the reproductive condition of the common kilka, Clupeonella cultriventris, the somatic condition and reproductive characteristics were studied by histological analysis. A total of 800 specimens from the Bandar Anzali coast on the Caspian Sea were sampled. The gonadosomatic index (GSI) for females and males attained maximum values in May in the first period of sampling and in March-April in the second period, suggesting temporal variations in spawning activity. The pattern of oocyte frequency distribution demonstrated that the common kilka is a batch spawner with group-synchronous oocyte development. The estimated relative batch fecundity was 6718 oocytes g–1. A low level of atresia (4.7%) during the spawning season showed that this species was in optimal somatic condition. This weakens the hypothesis that abundance of the ctenophore (Mnemiopsis leidyi) in the Caspian Sea, as a food rival for kilka, influences the body condition and subsequently the reproductive capability of this species.