Relative growth and morphological sexual maturity of the caridean prawn Macrobrachium villosimanus (Tiwari, 1949) (Decapoda: Palaemonidae)

Reproductive success for crustaceans depends on the transition from juvenile to adult, which can be estimated by analysing relative growth. To this end, the present study focused on the relative growth of appendix masculina length (AML), hatchery chamber width (HCW), body length (BL) and body weight (BW) in relation to carapace length (CL) of Macrobrachium villosimanus to estimate the morphological sexual maturity using the least squares method. Data for each relationship were repeatedly partitioned into two size-delimited subsets (juvenile and adult stages), considering a CL value as a hypothesized transition point. Analysis of the residuals sum of squares indicated two separate linear regressions fit the data better than a single linear regression. The study results indicated a discontinuity in allometry at 17.9 mm CL for CL versus AML, and at 15.6 mm CL for CL versus HCW relationships. These observed transition points could be associated with morphological sexual maturity of M. villosimanus. The BL and BW growth rate in relation to CL significantly decreased in males, but increased in females after reaching the morphological sexual maturity, demonstrating the existence of dimorphic growth. The increased growth rate after reaching sexual maturity in females probably corresponds to more space for the eggs and subsequent increased fertility. Accordingly, the present study indicated the secondary sexual characters (e.g. AML and HCW) play roles in attaining the morphological sexual maturity necessary for reproductive success and for ensuring the life cycle of this species.