Twenty seven commercial Macrobrachium species are found in Asia and the Pacific Ocean. Most of them are inhabited in freshwater except few are exclusively marine oriented. Few species live in brackish water especially in the mouths of rivers. A close examination of M. idea males reveals that three distinct morphotypes based upon size ranking, the ratio of claw length to body length (relative claw length) which included small male (SM), medium sized male (MS) and bigger sized male (BS). The mating behaviors of three different males 4 experiments were conducted by (1) 3 BS males (90-100 mm) vs. female (50-75 mm); (2) 3 MS males (60-75 mm) vs. female (50-75 mm); (3) 3 SM males (45-55 mm) vs. female (50-75 mm); (4) 1BS male, 2 MS males and 3 SM males vs. female (55-75 mm). The mating behaviour of M. idae was divided into four phases such as (I) Contact: When the male recognize the pre-mating female, it moves towards the female and starts approaching her. (II) Guarding: During this behaviour, the male encircled the female with his second pereiopods in a way that her tail region. (III) Mounting: After shell getting slightly hardens; the male grasps the female and begins to mount the female. After that using third and fourth pereiopods male started to clean the brood chamber to deposit the spermatophore. (IV) Mating: Took place when the female turned on her back, so that her ventral side was up. Next moment the spermatophore was ejected and deposited on the ventral median thoracic region of the female. After mating the pair was separated and again the male protects the female until the shell hardens completely. The 89.46% of the females were successfully fertilized in the presence of BS males and only 4.56% failed to become berried. In the cases of MS and SM males, successful fertilization was happened in 34.5% and 38% of the females and infertility was recorded for 34.37% and 40.99% of the females, respectively. The reproductive success of the BS male was significantly higher than that of the other two morphotypes (P<0.05).