Growth and reproductive pattern of the caridean shrimp Palaemonetes argentinus (Decapoda:Caridea) in southern Brazil

Abstract

In crustaceans, due to the absence of permanent hard parts which can be used for age determination, methods on length frequency distribuitions (e.g., Modal progression Analysis - MPA) are commonly employed for ageing. However, the linkage of the coborts followed during a period of time, brings uncertainty to the analysis. The present study suggests inclusion of biological aspects to validate the parameters estimatcd by the von Bertalanffy growth model (VBGM). The population of Palaemonetes argentinus analyzed here inhabits a closed lagoon near the Patos Lagoon (Lagoa dos Patos) estuary. Sample were collected fortnightly from june/1996 to December/1997 and carapace growth was estimated by using the VBGM. Biological aspects such as reproductive season, sex ratio and maximun carapace lengh were used to validate VBGM parameters. The growth paramets estimated were L=8.00 K=0.29/month; =0,34 for females and L= 6.67; K=0.34/month; =0.38 for males. The main reproductive season is spring, and brooding females were observed along the year, except on june-july/1996 and May-June/1997. The mean size of first maturity estimated was 6.5 (CL-mm). The validation of the VBGM parameters by using biological aspects has showed choerent results, reducing the uncertainty in choosing the modal groups that really describe the individual growth of the species.