In crustaceans there is a competition for mating especially among the males. The aggressive and dominant males win over less aggressive and subdominant males. The male reproductive success depends on male-male competition and aggression. This is very common in polygamous species. The individuals who are at a competitive disadvantage sometimes adopt an entirely different group of reproductive behaviours. The present study evaluates the relative reproductive potential of three different size males of M. idae by examining their mating strategy in close quarter in an aquarium and to arrive at a qualitative evaluation of each of these morphotypes (representing three different developmental stages) according to each type’s specific physical characteristics, typical behaviour and probability of achieving successful fertilization.Citation: Soundarapandian P, Sudhakar S, Varadharajan D, Dinakaran GK (2013) Mating Behaviour in Different Size Males of Macrobrachium idae (Heller, 1862). J Cytol Histol 5:205.