Relative growth, sexual dimorphism, and sexual maturity of the freshwater shrimp Macrobrachium jelskii (Miers, 1877) (Caridea: Palaemonidae)

Macrobrachium jelskii is an endemic shrimp species of South America, with a wide geographical distribution. Although there have been some studies on this organism, information regarding the relative growth of body structures has never been fully explored. In this regard, we aim to analyse the relative growth of this species, in order to investigate the developmental pattern between juveniles and adults, as well as to estimate the morphological sexual maturity (MSM). For morphometric analysis and MSM estimation, the following structures were measured: carapace length (CL); abdomen length (AL); propodus (CPL) and dactyl length (DL) of the second pair of pereopods; second pleonal pleuron width (SPW); and appendix masculina length (AML). We observed developmental differences between juveniles and adults, especially in males. The MSM size for males was estimated at 7.47 mm CL, while for females it was 8.77 mm CL. Females exhibit significantly larger sizes compared to males. Our study reveals divergent energy allocation between juvenile and adult M. jelskii, with males and females reaching MSM at different sizes. The development of these structures with varying allometric constants throughout life stages suggests a strong connection to reproductive behaviour, meeting the specific needs of each life stage's behavioural repertoire.