Growth patterns and some biological characteristics of Leuciscus aspius (Linnaeus, 1758) in the southern parts of the Caspian Sea

Growth pattern and some biological characteristics of Leuciscus aspius Linnaeus 1758, in the southern parts of the Caspian Sea were studied. Some 96 fish specimens were caught at Guilan, Mazandaran and Golestan provinces from October 2018 to September 2019. Fish were at the age classes of 1+ to 4+ years. The highest percentage of fish were at the age class of 2+ (33.72%), while the lowest at 4+ years (11.62%). Male/female age ratio was 0.68-1. Total length varied between 29-54 cm, fork length between 25-49 cm and the body weight was 213- 985 g. The mean total length was 38.91±5.57 cm, fork length 35.06±5.23 cm and mean weight was 639.74±87.27 g. The lowest growth coefficient rate was observed at the ages of 1-2, while the highest at 3-4 years. The mean condition factor (CF) was 0.87±0.22, hepatosomatic index (HSI) was 0.41±0.17 and gonadosomatic index (GSI) was 0.56±0.17. The length- weight relationship of all specimens was W= 0.0204 L2.7361, in males was W= 0.0189 L2.7648 and in females W= 0.0217 L2.8867. According to the obtained b values, the growth pattern of L. aspius was negative allometric meaning that weight and length growth did not follow similar rate. Length growth was faster which resulted in thin fish specimens. Moreover, condition factor below 1 (CF<1) reflects that L. aspius did not have favorable feeding ground in the study area which has led to lower growth. Factors like pollution, destruction of rivers, scarcity of food sources and overfishing could be responsible for these problems.