This study was carried out to determine growth and mortality parameters of mud crab R. harrisii during a period of 12 months from May 2017 to April 2018 in northeast parts of Gorgan Bay-southeast Caspian Sea. A total of 307 crabs were collected using small beach scene and snail traps, including 120 females and 187 males. The total length of the male crab ranged from 7.01 to 18.36 mm with a mean of 13.07±0.16 mm, while that of females ranged between 5.56 and 8.92 mm with a mean of 11.02±0.02 mm. The largest mean value of observed lengths, which is 20.52±0.50 mm, was in November and the lowest was recorded in May with the value of 12.84 ± 0.81 mm. Based on von Bertalanffy growth model, L-infinity and K parameters were 23.5cm and 1.63 years^-1 for females and 22 cm and 1.1 year^-1 for males. Using carapace width, the parameter of Lm50 was 12mm. The index ofɸ -Munro was 2.97 and 2.95 for males and females respectively. The results on growth and reproduction of the species provided in this were the first one and could be useful in conservation plans of the species and Miankaleh wildlife refugee area as well.

Keywords: Gorgan Bay, Crab, Distribution, Longitudinal frequency

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