This study investigates the population structure of the Brazilian sardine, Sardinella brasiliensis, Brazil's primary fishery resource, by analyzing growth rates across its geographical distribution. Historically, the population is divided into a northern (22-24°S) and a southern stock (26-29°S), with a central area (25°S) hypothesized as a shared juvenile feeding ground. Individuals are believed to return to their natal stocks upon reaching sexual maturity. To test this long-standing hypothesis, this research compared the growth rates of 50 sardines, aged 2 to 7 years, from the northern, central, and southern areas. The methodology involved measuring the average distance between growth rings on otoliths (ear stones) and analyzing these distances using a generalized additive model for scale and shape, followed by Dunn's tests for multiple comparisons. The analysis revealed significant differences in growth patterns at specific life stages. For the earliest life stages (first and second post-nuclear rings), growth in the central area was distinct, supporting its role as a shared nursery ground. At ages 1 and 2, significant differences emerged between the southern area and both the northern and central areas but not between the north and central regions, indicating a mixing of stocks. By age 4, differences were found solely between the established northern and southern stocks, with no distinction between the central area and either stock. These growth rate findings robustly corroborate previous studies using geometric body shape and otolith chemistry. The results confirm the historical population model: juveniles from both stocks cohabitate and feed in the central area before returning to their respective northern or southern regions around their fourth year of life. This research provides critical evidence for the species' population dynamics, offering vital insights for its sustainable management and conservation.