Some biological characteristics of oriental river freshwater prawn Macrobrachium (Macrobrachium nipponense) Holthuis, 1951 (Decapoda, Palaemonidae) in Alagol Lagoon, Iran

Some biological aspects (i.e. sex ratio, size frequency distribution, recruitment, relative growth rate) of Oriental river freshwater prawn Macrobrachium (Macrobrachium nipponense) were investigated in Alagol Lagon, Caspian Sea, Iran. Sex ratio, size frequency distribution and relative growth rates were used to investigate sexual dimorphism. A total of 429 prawns were monthly collected during one year. Density of female prawns significantly was higher than males (205 (47.29%) females versus 224 (52.2%) males. In general, male prawns were significantly larger and heavier than females. The size frequency distribution was not normal (ks = 1.94 , p=0.001 ) for either sex.The average (±SD) carapace length was about 65 ± 10.79, and 53.10 ± 9.07 mm for males and females, respectively. The male prawns had lonegr lifespan and larger size than females. The spawning period of the present species in the Alagol lasts for four months from the beginning of April to end of July with a peak in May. This finding demonstrates that the higher allometry in males occurs as a function of dominant position over females. A positive allometric and a negative alometric growth were observed for the TW/Carl ratios in male and female prawns, respectively. This is also indicated by the larger weight of males than females.

کلیدواژه ها:

Oriental river prawn ، Population structure ، Growth rate ، Sex ratio ، Alagol Lagon ، Iran.