Length-weight, length-length relationships and condition factor of Rutilus kutum (Actinopterygii: Cyprinidae) from the southern Caspian Sea, Iran

Fish stock assessment in the Caspian Sea requires employing some growth indicators such as length-weight relationship (LWR). Size determination in fish is more biologically relevant than age, because several ecological and physiological indicators are more size-dependent compared to age-dependent. This study aims to examine the length-weight relationship and condition factor of Rutilus kutum (Kamensky) from the southern Caspian Sea. 218 fish samples were caught using a gill net from Anzali, Astara, Kiashahr, Sari and Torkaman Port from September 2018 to February 2019. Negative allometric growth patterns were observed in Sari and Torkaman Port and positive allometric growth patterns were found in Anzali, Kiashahr and Astara stations. The fish caught from Anzali displayed the maximum condition factor. LWRs are not continuous over the year and LWR indices may vary significantly due to biological, food availability, temporal and sampling factors, and also by fish health and sex. Relative weights in fisheries studies can be used for comparing condition across different populations and species. Investigations carried out indicate that growth of R. kutum in recent years has decreased.