The biological characteristics of Clupeonella cultriventris Caspian In southern coast and the impacts of Mnemiopsis leidyi Invasion on the Caspian ecosystem

Kilka belongs to pelagic fish in the Caspian Sea and they feeds on zooplankton. They are the most abundant fishes of the Caspian Sea. There are three species of kilka fish included of anchovy (Clupeonella engrauliformis, Svetovidov 1941) big eyes (C.grimmi, Kessler, 1877) and Common kilka (C. cultriventris Bordin, 1904). All three species have been existed in Iranian coastal waters and common kilka had minimum relative frequency. 1.34, 2.5 and 5.5% of total catch belong to it in 1990-91, 1997-98 and 1998-99 respectively. After Mnemiopsis leidyi invasion in the Caspian Sea, relative frequency of this fish increased more than 10%. During 1997 to 2001, some important indexes such as length frequency, weight, sex, sexual maturity stages and age of this fish were studied in catch regions. Spawning of common kilka occurred in spring in 1997-99 while in 2000-2001 spawning started later, in mass on April and continued to August. We didn’t see any female at maturity stage VI_II, and stage V was rare. The fork length average was reduced from 92.7mm in 1997 to 81.5mm in 2000 and increased to 88.3mm in 2001, but fork length limits were less. The female was dominated. Age structure had 6 age classes (0+ - 5+). Age classes 0+ - 3+ included 95% during 1997-1999. In 2000 age classes 0+ and 1+ were reduced and 2+ - 4+ were 93.8%. Biological characteristics such as length and age indicated that common kilka population tolerate a pressure but probably because of dispersion of habitat its share in commercial catch has increased during recent ears.