HELMINTHS AS BIOLOGICAL TAGS FOR FRANCISCANA (PONTOPORIA-BLAINVILLEI)(CEFACEA, PONTOPORIIDAE) IN ARGENTINEAN AND URUGUAYAN WATERS

The helminth fauna of 46 franciscanas, Pontoporia blainvillei, from Ne cochea and Claromeco (Argentina) were compared with previous records f rom Punta del Diablo (Uruguay) in order to establish whether the dolph ins mixed freely between localities or formed isolated population unit s (stocks), at least temporarily. The nematode Anisakis simplex appear ed in Argentina, whereas A. typica did in Uruguay only. This could be related to the geographic distribution of each species. There were als o changes in the least common parasites and variations in the intensit y of infection of the acanthocephalan Polymorphus cetaceum, and presum ably, in the prevalence of the digenean Hadwenius pontoporiae. These r esults may be mainly explained by the environmental differences of eac h locality. However, as the sampling data differed between localities, temporal causes cannot be discounted for the quantitative variations. The overall results suggest that P. blainvillei might be sedentary, a t least in spring-early summer, hence showing separate stocks, despite the relative closeness between localities. The potential value of the parasites observed as biological tags for populations of P. blainvill ei is also discussed.