The present investigation aimed to estimate the individual growth and mortality of an invasive species found in the estuarine region of Patos Lagoon (Southern Brazil). For 20 months crabs were sampled, and in the laboratory specimens of Rhithropanopeus harrisii (Gould, 1841) were measured (carapace width, CW, and weight). Carapace width data was utilized for a modal progression analysis and to estimate the individual growth curve (von Bertalanffy growth model), and a size-converted catch curve. Von Bertalanffy parameters estimated were CW ∞ = 16.92 mm and k = 1.28 year-1. Maximum longevity was estimated at 3.5 years. Instantaneous total mortality was estimated at 2.17 ± 0.30 year-1. It has been suggested that longevity may be explained by a low predation impact on R. harrisii, which, as a consequence, may lead to slow individual growth of this species in the estuarine region of Patos Lagoon.