Study on some reproductive biology aspects of Caspian roach, Rutilus caspicus (Yakovlev, 1870), on the south-east coasts of the Caspian Sea

In this study, some aspects of the reproductive biology of Caspian Roach caught by beach seining were investigated along the southeast coats of the Caspian Sea in the period of 2019-2021. From a total of 317 samples of caught fish (144 males and 173 females), the sex ratio of male to female was 1:1/2, which was not statistically significant with the expected ratio of 1:1 (p>0.05). The average fork length (± standard deviation) was 15.6 ± 2.63 cm (with a range of 10.6-25.5 cm) for males and 18.7 ± 3.70 cm (with a range of 11.3-32-5 cm) for females. The range and average weight for males were 18-214 g and 60.7 ± 36.20 g, respectively, and 22-502 g and 120.5 ± 74.76 g for females, respectively. The minimum, maximum, and average absolute fecundity of R. caspicus were estimated as 6707, 51438 and 18773 ± 9800 eggs, respectively. The mean relative fecundity was estimated to be 152 ± 33 eggs/g and 967 ± 367 eggs/cm in relation to the total weight and fork length, respectively. The absolute fecundity of the species increased with an increase in the length and weight of fish with coefficients of determination of R2= 0.62 and 0.68, respectively, so that the range of fecundity in the length range of 14.5-15.5 cm is equal to 6707-11807 eggs and in the length range of 27-32 cm was estimated as 35813-42693 eggs. According to the results, sexual maturity at stages IV and V is present in all sampling months for females of R. caspicus. The mean length (fork length) at first maturity (Lm50%) of females R. caspicus was 13.8 cm. The highest value of Gonadosomatic index (GSI) for males was observed in February with a value of 7.08, and for females in March with a value of 16.06 which decreased to 15.96 in April. Considering that the peak value of GSI and the high percentage of V maturity stage of R. caspicus is observed in March and April; it can be prohibited to catch this species in this time.