Stocks and migrations of the demersal fish Umbrina canosai (Sciaenidae) endemic from the subtropical and temperate Southwestern Atlantic revealed by its parasites

The Argentine croaker Umbrina canosai (Sciaenidae) is a demersal fish distributed along the coasts of central Brazil, Uruguay and northern Argentina. In recent years, an increasing impact of commercial fishing has been reported, representing a high risk of collapse for this resource and enhancing the need of knowledge on its population structure. In the southwestern Atlantic fish parasites have already been demonstrated to be useful as biological tags for such purposes in other resources and are, here, analyzed to delimit the stocks of U. canosai and confirm its migratory route between Brazil and Argentina. A total of 193 Argentine croakers, distributed in six samples from five different localities, were examined for metazoan parasites. Umbrina canosai harboured 28 parasite taxa among which long-lived larvae of Grillotia carvajalregorum, Corynosoma australe and Hysterothylaciurn sp., and the adult monogenean, Nicolasia canosorum, were the most prevalent. Host size was related to both diversity and structure of parasite infracommunities in the whole sample, but no effect of fish sex was detected. The multivariate analyses, at both infracommunity and component community levels, showed clear geographic patterns with fish from Rio de Janeiro differentiated from their southern counterparts, confirming the presence of two discrete stocks. The results also evidenced the homogeneity of samples caught in southern Brazil and Northern Argentina, regardless of the long distances separating them, confirming the existence of a single stock with seasonal migrations between southern Brazil and northern Argentina. The information on the stock structure and migratory pathways of U. canosai represents a first step to the implementation of measures for a sustainable management of this important fishery resource.