Common Carp (Cyprinus carpio) and Roach (Rutilus rutilus) are important species withhigh economic value in the catch composition of bony fish in the Iranian waters of the Caspian Sea, accounting for an average of 2% and less than 0.1% of the total annual catch. Because of important of spawning studies of species in fisheries management, it was necessary to do research on the current situation of spawning activities of two species of C. carpio and R. rutilus and compare it with previous results.
Initially, this study aimed to investigate the entire Iranian coasts of the Caspian Sea in the three northern provinces, but due to the lack of financial allocation, the number of samples collected in the coastal waters of Mazandaran province was insignificant and negligible, and also in the coastal waters of Gilan province Failed. Therefore, the collected data is the result of completely random sampling of the catch composition of the beach seine fishing cooperative companies of Golestan province from October 7, 2019 to April 14, 2021 for two commercial fish species, C. carpio and R. rutilus.The minimum and maximum fork length of C. carpio were 17 and 50 cm, respectively, with an average (±standard deviation) of 31.1±6.7 cm, and minimum and maximum weight of the species was 104.0 and 2530.0 g, and the average weight of the samples was calculated as 573.4±350.6 g. For R. rutilus, the minimum and maximum fork length were 10.6 and 32.5 cm, respectively, averaging at 17.2 ±3.7 cm. The minimum and maximum weights of the R. rutilus were recorded as 18 and 502 g, respectively, with an average of 91.8±67.4 g.
The sex ratio of male to female for C. carpio and R. rutilus was calculated to be 1:1.03 and 1:0.83, respectively, which was not significantly different in both species with a hypothetical ratio of 1: 1 (p> 0.05). Based on the frequency of different stages of sexual maturity and also the trend of changes in gonadosomatic index (GSI), the peak spawning of C. carpio occurred intwo periods, i.e.December-January (weak peak) and March-April (strong peak), and for R. rutilus only one peack of spawning in March-April was observed.
The average absolute and relative fecundity of C. carpio were 429310±233479 and 668±319 eggs per female fish, respectively, and for R. rutilus were 18773±9877 and 152±33 eggs per gram of fish body weight, respectively.There was a direct relationship between the amount of absolute fecundity and length and weight in both mentioned species, which for C. carpio, the above relationship was expressed as the independent parameter Fec=547.63w+60676 (R2=0.72) and Fec=28524FL-512188 (R2= 0.61), respectively, and for R. rutilus, Fec= 110.46w+4779.6 (R2= 0.68) and Fec= 2733.8FL-32633 (R2= 0.63) were obtained, respectively.
The average length at sexual maturity (Lm50%) of C. carpio was 27.7 cm, and forR. rutilus was 13.8 cm, which compared to the results of previous studies, decreased by 3.8 cm for C. carpio and 1.7 cm for R. rutilus.
The relationship between length (fork) and weight of C. carpio by male and female was W=0.024FL2.8916 and W=0.0198FL2.9519, respectively, and for R. caspicus relationship was as W=0.0065FL3.2818and W=0.0099FL3.1711, respectively, which based on statistical tests, both males and females had allometric growth pattern.
The age range of the samples for C. carpio was between 1 to 9 years and the highest frequency of catches (26.6%) was observed for the fish with the ages of  4 years. For R. caspicus, the age range was between 1 and 9 years, with the highest frequency of fish (34.6%) was observed in the ages of 1 years.
Due to the temporal coverage of the peak spawning of C. carpio and R. rutilus with the end of the beach seine fishing period for bony fish, it is suggested that the end of the fishing season be announced from the end of March in the coastal waters of Golestan province. Also, due to the decrease in the length at sexual maturity of C. carpio and R. rutilus species, which is expected to be due to illegal fishing and the use of non-standard mesh size of the current beach seine net and the fishing pressure on the fish population caused the lengths of the fish to decrease, the modification of the existing mesh size of the beach seine net based on future studies along with the use of the optimal fishing effort level suggested by existing studies is necessary to rebuild the stocks and achieve responsible fishing.
Keywords: C. carpio, R. rutilus, spawning, Lengh at first maturity, Fishing ban, Caspian Sea
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