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RESEARCH PRODUCT

Metazoan parasites in meagre and gilthead seabream aquaculture: monogeneans, from biology to infection management

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Pathologies represent a relevant bottleneck for aquaculture development and must be taken into account in the selection of potential species for diversification. Determining pathogens affecting new and traditional cultured species as well as their potential impacts on fish health becomes essential for optimising the development and viability of fish productions. Among pathogens, monoxenous metazoans, such as platyhelminth monogeneans, have a marked influence on fish health, especially in aquaculture where they cause significant economic losses in the main fish-farming industries. Population dynamics in host-parasite systems are modulated by environmental conditions. Therefore, effective management of monogenean infections requires a good understanding of the host-parasite relationship as well as the abiotic factors affecting the balance between both organisms. Integrating biological and applied aspects into routine management procedures becomes essential to minimize the infection risks in fish farming facilities and design accurate strategies under changing environments. The present thesis aims to identify the parasite fauna of Mediterranean sciaenid fishes with potential for species diversification in aquaculture and compile information of key biological aspects for the management of potentially hazardous monogeneans in the gilthead sea bream and meagre cultures, especially under the seasonal environmental conditions occurring in the Western Mediterranean Sea. Altogether, results of this PhD study have led to the following conclusions: The parasite fauna of Sciaena umbra, Umbrina canariensis and Umbrina cirrosa in the Western Mediterranean Sea includes thirty-four parasite taxa, with twenty metazoan parasites being identified in each sciaenid host. The parasitological analysis allows detecting new parasite records together with previously reported species; 9 new host records and 11 previously reported parasites are registered in S. umbra while 13 new host records and 7 previously reported species are found in U. canariensis as well as U. cirrosa. One new locality record was also found in U. canariensis. Four parasite taxa constitute new host records for the three sciaenid species (Lecithocladium excisum, Lernaeolophus sultanus, Rhipidicotyle sp. and Tetraphyllidea gen. sp.) while four previously reported species are also shared by these hosts (Caligus cf. dakari, Diplectaninae gen. spp., Lernanthropus gisleri, Stephanostumum bicoronatum). Among parasite species first reported in these sciaenid hosts, none is common in S. umbra, while 4 species are common in U. canariensis (Calceostomella inermis, Contracaecum sp., Hysterothylacium fabri, S. cesticillus), and 3 in U. cirrosa (Rhipidocotyle sp., Tetraphyllidea gen. sp. and Zoogonus sp.). Among previously reported parasites, 5 taxa are common in S. umbra (Calceostomella inermis, Diplectaninae gen. spp., Gnatia vorax, Hysterothylacium fabri and Siphoderina aloysiae), 3 in U. canariensis (Anoiktostoma elongatum, Diplectaninae gen. spp and Dycheline elongatus) and 5 in U. cirrosa (C. inermis, Diplectaninae gen. spp., D. abbreviates and Lernanthropus gisleri, S. bicoronatum). Most parasite species constituting the parasite fauna of the Mediterranean sciaenids are generalist. Only 1 sciaenid specific parasite species was included in the common parasite fauna of S. umbra (S. aloysiae), 1 genus-specific (A. elongatum) and 1 species-specific parasite (D. elongatus) in U. canariensis and 1 sciaenid-specific parasite (L. gisleri) and 1 species-specific parasite (D. abbreviatus) in U. cirrosa. The majority of the common species parasitizing S. umbra, U. canariensis and U. cirrosa showed seasonal differences in prevalence over 10% while mean intensity differences between seasons were comparatively lower and showed by fewer species. Sciaena umbra: seasonal differences between prevalences were equal or below 25% in three of the four common species while higher in S. aloysiae (30%), which also was the only species showing differences higher than 5 specimens/fish of mean intensity (10 specimens more in summer). Umbrina canariensis: seasonal differences between prevalences were equal or below 25% in four of the six common species while higher in C. inermis (30%) and S. cesticillus (92.6%). Seasonal differences between intensities were usually low ( winter-spring) and A. elongatum (winter-autumn > spring-sum-mer), differing in more than 35 specimen/ fish between seasons. Umbrina cirrosa: seasonal differences between prevalences were above 25% in all the species except for S. bi-coronatum (16.9%). Seasonal differences between intensities were usually low (60 clamp pair numbers) are exclusively found on fish more than 18.3 cm long (standard length), whereas mid-anterior and posteriormost clamps were generally larger in larger gilthead sea breams. The posteriormost and mid-anterior clamps achieve their maximum dimensions in early post-larval and mature stages, respectively, thus suggesting that host features modulate parasite size from the initial stages of parasite development. By contrast, gill location and parasite abundance are of minor relevance on intraspecific size variations of mature stages of S. chrysophrii.