Servizio Comunitario di Informazione in materia di Ricerca e Sviluppo - CORDIS

Final Activity Report Summary - PARAQUAM (Parasite pathogens in new species of Mediterranean aquaculture: an experimental approach)

Species diversification has become a major challenge to Mediterranean aquaculture and, thus, the study of potential pathogens that might affect candidate species under extensive culture conditions are especially important. The current project aimed at the elucidation of several aspects of the biology, life cycle and pathology of different monogenean, digenean and myxozoan parasites of the greater amberjack Seriola dumerilii, several sparid fishes, with special focus on the sharpsnout seabream Diplodus puntazzo, the striped seabream, Lithognathus mormyrus.

A part of the project was dedicated to taxonomic and community studies of parasites on wild fish, keeping in mind that any infection in sea cages is derived from the wild, and that various species function as vectors or reservoirs for diseases. With regard to S. dumerilii, two new species of sanguinicolid digenean genus Paradeontacylix were described, which were found to inhabit the blood vessels of the gill arches. Only one of the sanguinicolids, P. balearicus was found to provoke important pathology and mortalities due to the accumulation of large numbers of eggs in clots in the gill capillaries resulting in the obstruction of blood vessels, whereas the eggs of the other species, P. ibericus, did not form clots or cause pathological changes.

The developmental stages of P. ibericus were described and parasite habitat selection in the definitive host and the development of sanguinicolidosis in experimental, inshore cultures of S. dumerili, was investigated. Population studies of the Paradeontacylix spp. using ribosomal and mitochondrial sequences as well as morphological datasets showed that geographic isolation is mirrored in genetic distances leading to speciation of the two parasite species in the Mediterranean when compared with similar species from Japan. Thereby, worldwide speciation seems to mirror ancient tectonic events.

Research on monogenean gill parasites focussed on the effect and the life cycle of Zeuxapta seriolae on S. dumerilii which was compared with that of Sparicotyle crysophrii on the well-established aquaculture species Sparus aurata. In D. puntazzo, the species composition of monogeneans belonging to the genus Lamellodiscus, their distribution on the gill filaments and the system of anchorage to the gills was studied. For both, Z. seriolae on the amberjack as well as for Lamellodiscus spp. on D. puntazzo, controlled maintenance in artificial culture systems was established and was used to study the life cycle, biological and pathological aspects of the infections.

A new line of research focussing on the microscopic spore-forming myxozoan parasites was successfully established at the host institution. Unicapsula pflugfelderi was described from L. mormyrus, where it was found to form large plasmodia inside the muscle fibres, which might result in rejection of the fish by the consumer, a problem which has to be kept in mind with regard to future culture intents of L. mormyrus. In D. puntazzo, the myxozoan Ceratomyxa diplodae was found to cause pathological changes which manifest themselves in alternated blood cell counts and massive leukocyte invasion in the liver, a study which is yet on-going. The electron microscopic description and phylogenetic study based on the 18S rDNA of two new myxozoan species, Kudoa trifolia and Kudoa unicapsula from mugilids, which are traditionally cultured in the Valencian area, revealed new, unusual morphological features for Kudoa.

Finally, one part of the current project focussed on in-depth taxonomical and parasite-community studies which were conducted on several host-parasite systems. Based on a combination of morphology and different ribosomal genes, parasite biodiversity patterns in Mediterranean mugilids were analysed with special emphasis on the trematode family Haploporidae. Due to the importance of the sparid B. boops as a vector for diseases in cultured fish, composition and structure of parasite communities were examined along a gradient of fish sizes and in different geographical regions. In cod, Gadus morhua, different algorithms for modelling parasite communities, e.g. random forests, were tested.

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Poligono de la Coma s/n