Reproductive characteristics of exotic oriental river prawn (Macrobranchium nipponense De Haan, 1849) in the wetlands of Almagol, Alagol and Ajigol, Golestan Province, Northern Iran

The oriental river prawn (Macrobranchium nipponense) is a commercially important farmed species in some countries of Southeast Asia, and an exotic one distributing in lakes, reservoirs and aquaculture ponds in the northern provinces of Iran. This study was conducted to investigate the reproductive characteristics of this species in Alagol, Almagol and Adjigol wetlands. A total of 1284 specimens were collected, and their biometrical data measured. The sex ratio of male to female for the whole region was estimated to be 1: 1.29. This ratio was different between wetlands. Females were dominated the length groups of 12-20 mm, while males were more frequent in length groups of 24 mm and larger. The spawning season was started in early spring and lasted till mid-summer. The mean condition factor was estimated 1.038 for males and 0.64 for females. The mean batch fecundity ranged from 342 in Alagol to 3722 in Adjigol. The relationship of batch fecundity with carapas length and total weight showed an exponential model. The highest volume of the oocytes was observed in Alagol, and the lowest one in Adjigol. The carapas length at first maturity was estimated as 12.1 and 13.2 mm for males and females, respectively. Its high fecundity, small first length of maturity, and spawning during warm-water fish farming makes prawn broadly distributed in the area, therefore it is difficult to eliminate it from the inland water ecosystems.