The primary aim of the present study was to conduct a 1-yr parasitological survey of a Mytilus galloprovincialis mussel population from the Aveiro Estuary, Portugal. In addition, we attempted to assess the host response to parasites by examining host histopathology, including an evaluation of hemocyte infiltration and parasite encapsulation. The parasites present (prevalence) included the following: 1 protozoan, Nematopsis sp. (70%); 1 turbellarian, Urastoma cyprinae, (39%); 2 trematodes, Diphtherostomum sp. (58%) and Prosorhynchus crucibulum (0.3%); 3 crustaceans, Bathylaophonte azorica (0.3%); and 2 species of Mytilicola sp. (3.5%), M. intestinalis and M. orientalis. Highest prevalences for the most abundant species occurred in summer and autumn. Histological sections of the mantle of infected mussels revealed a marked reduction in the reproductive tissue, indicating that P. crucibulum invades the mussel and promotes a severe damage to its reproductive capacity.

We studied the use of parasites as biological tags for discriminating fish stocks of Aphanopus carbo (Osteichthyes: Trichiuridae) from Portugal (Sesimbra on the mainland, Madeira and the Azores). Sixteen different metazoan parasites were found (14 from Madeira, 9 from Sesimbra and 7 from the Azores). Some parasites occurred only in fish from Madeira. The prevalence and mean intensity of the infection was recorded for each parasite and locality, and their values were statistically compared between the three sampling localities and related to host length classes. The differences between some of these parameters were statistically significant among the three localities or between two of them. It is suggested that 6 parasites (Tentacularia coryphaenae, Sphyriocephalus tergestinus, Campbelliella heteropoeciloacantha, Anisakis spp., Bolbosoma vasculosum and unidentified Acanthocephala larvae) can be used as biological tags to discriminate Portuguese stocks of Aphanopus carbo