Morphometric differences between two exotic invasive freshwater caridean species (genus Macrobrachium).
The prawns Macrobrachium amazonicum and Macrobrachium jelskii, have been introduced in the southeastern Brazilian region. Thus, it becomes necessary knowing the reproductive aspects of these invasive species. This study aimed to analyze the relative growth and to estimate the morphological sexual maturity of the freshwater prawn species M. amazonicum and M. jelskii. We collected monthly samples from January through December 2010 in the Rio Grande riverbank. Prawns were measured to their cephalothorax length (CL), length of the pleura of the second abdominal somite in females (PL) and length of the appendix masculina (AML). We analyzed 2937 specimens of M. amazonicum (628 males and 2,309 females) and 2167 specimens of M. jelskii (504 males and 1663 females). We observed different allometric patterns in the relative growth of the AML and PL (both more accentuated in M. amazonicum) between the species. The present results indicate that these species adopt different reproductive strategies, possibly representing adaptations that may have facilitate their establishment in the Rio Grande riverbank. When comparing our results to the ones obtained in previous studies, we observed that the reproductive traits of both species indicate a marked phenotypic plasticity.