Abstract
The aims of this study were (1) to compare the structure and composition of parasite assemblages of the flounder Xystreurys rasile in two regions of the Argentine Sea in order to evaluate the hypothesis for the existence of different stocks, and (2) to test the hypothesis for X. rasile migration from the Argentine–Uruguayan Common Fishing Zone ( AUCFZ ) towards more southern waters during spring. Parasitological evidence shows that at least two stocks of X. rasile inhabit the coastal and shelf waters of the northern Argentine Sea, one in El Rincón and the other in the AUCFZ . These stocks should be considered as discrete entities in management plans to ensure a sustainable use of these resources. The results also confirm the existence of migratory patterns in the northern stock.