ABSTRACT Population biology, growth and reproductive aspects of the amphidromous shrimp Palaemon pandaliformis (Stimpson, 1871) were investigated in a Neotropical river of northeastern Brazil. The specimens were collected every month from September 2009 to August 2010. Total and monthly sex ratios deviated in favour of males. Von Bertalanffy growth parameters indicated that the females grew more rapidly, reached larger sizes, and had a longer life span than males. We also observed continuous reproductive activity and juvenile recruitment throughout the year. Relations between the number of eggs (fecundity) and body size indicated that fecundity in females increase with size. Compared with previous results, some population biology parameters of the freshwater population of P. pandaliformis differ from estuarine populations. The reproductive aspects analyzed here and their comparison with other marine species were consistent with the hypothesis that Palaemonidae species are undergoing an adaptation process and colonizing fresh water environments.

Foram descritos o crescimento relativo e a maturidade sexual de uma população de Palaemon pandaliformis Stimpson, 1871 do rio Salsa (Nordeste do Brasil). As coletas foram realizadas mensalmente entre setembro de 2009 e agosto de 2010. As fêmeas foram maiores, mais pesadas e exibiram um coeficiente alométrico (b) maior que os machos. Apenas a relação comprimento de carapaça vs. comprimento de pleura nas fêmeas, apresentou uma diferença significativa no padrão de crescimento relativo, evidenciando a muda da puberdade. Esta relação é estritamente correlacionada aos eventos reprodutivos e ao sucesso deste em fêmeas de carídeos. O comprimento da carapaça em que 50% das fêmeas estão maduras (CL50) foi estimado em 4,53 mm. Não foi possível comparar os resultados de CL50 obtidos devido à falta de estudos enfocando a espécie. A comparação foi feita através do tamanho da menor fêmea ovígera capturada (3,81 CL mm), o qual está dentro da amplitude de tamanho registrada para estuários localizados em latitudes mais elevadas. Este trabalho aponta a falta de estudos para este gênero em ambientes dulceaquícolas, uma vez que estes são raros, mesmo em escala nacional e global.

This study comprises the description of relative growth and sexual maturity of a population of Palaemon pandaliformis Stimpson, 1871 in Salsa River (Northeastern Brazil). Samples were collected monthly between September 2009 and August 2010. Females were larger, heavier, and showed a greater allometric coefficient (b) than male specimens. Only carapace length vs. pleura length in females presented a significant difference in the relative growth pattern, indicating a puberty moult. This relationship is strictly correlated to reproduction and its success rate in female shrimps. Estimated carapace length in 50% of mature females (CL50) was 4.53 mm. It was not possible to compare obtained CL50 results due to a lack of studies on this species. Comparison was based on the size of the smallest captured ovigerous female (3.81 CL mm), which is within the scope of recorded size for estuaries located in higher latitudes. This study reveals the lack of research on this genre in freshwater environments on a national and global scale.