The sea-bob shrimp, Xiphopenaeus kroyeri, is one of the most important economic marine resources along the entire Brazilian coast. Nevertheless, despite its economic importance, no studies have examined the population genetics of this species. In this paper, we used ten allozyme loci to study the pattern of genetic structuring in X. kroyeri along the southeastern Brazilian coast. Seven of the ten analyzed loci were polymorphic, yielding observed heterozygosity values higher than those reported for other penaeid shrimps. The population from São Paulo was significantly different from the other two populations (Rio de Janeiro and Espírito Santo), which, in turn, seem to form a single panmitic unit. Therefore, our results clearly indicate that conservation policies for this species should consider the São Paulo population as an independent stock from those of Rio de Janeiro and Espírito Santo.

En el presente trabajo se utilizó análisis de aloenzimas para demostrar que los individuos en los agregados de la especie Anthopleura krebsi son monoclonales. Además, muestras simpátricas de las variedades roja y verde fueron comparadas genéticamente y ninguna diferencia significativa fue observada entre ellas (Identidad génica= 0.992), indicando que ellas no pertenecen a especies biológicamente distintas. Todos los individuos dentro de un agregado de la variedad roja resultaron ser idénticos para los cinco loci polimórficos analizados. Tal resultado sería extremadamente improbable (p<10 -11 ) si los individuos analizados hubiesen sido generados a través de reproducción sexual, confirmando así la presencia de reproducción asexual en esta especie.

In this paper we use allozyme analyses to demonstrate that individuals in Anthopleura krebsi aggregates are monoclonal. Additionally, sympatric samples of the red and the green colour-morphs of A. krebsi from Pernambuco, Brazil were genetically compared and no significant differences were observed between them (gene identity= 0.992), indicating that they do not belong to different biological species. All individuals within aggregates of the green colour-morph were found to be identical over the five polymorphic loci analysed. Such results would be extremely unlikely (P<10 -11 ) if the individuals analysed had been generated through sexual reproduction, thus confirming the presence of asexual reproduction in this species.