Transfer of Sparicotyle chrysophrii and Ceratothoa oestroides between wild and aquaculture fish inferred by ddRAD sequencing

Comunicación presentada en la 19th International Conference on Diseases of Fish and Shellfish, celebrada en Oporto (Portugal) del 9 al 12 de septiembre de 2019.[Introduction]: The monogenean Sparicotyle chrysophrii and the cymothoid isopod Ceratothoa oestroides are among the most devastating ectoparasites in Mediterranean aquaculture, causing losses in gilthead sea bream (Sparus aurata) and European sea bass (Dicentrarchus labrax) production. Their life cycles and modes of transmission have not been fully elucidated and molecular resources for their investigation are extremely scarce. Being attracted by signals from conspecifics in aquaculture installations, the food and shelter availability in the farms, wild fish are generally recognised as reservoirs for parasite transmission to farmed fish. Viceversa, cultured stocks may also act as reservoirs of infectious stages, as they are present in concentrated numbers and density, and potentially more susceptible to disease than wild fish.[Methodology]: The potential extent of transmission of these two ectoparasites between wild and farmed fish populations has been evaluated by genotyping-by-sequencing approach, double digest Restriction-site Associated DNA sequencing (ddRAD-Seq), to generate a genome-wide SNP marker dataset. Parasites sampling was done across four large Mediterranean farming areas in Spain, Italy, Croatia and Greece, representing the largest collection of genotypes obtained from aquaculture and wild fish populations (n = 600).[Results]: Expectedly, a considerable variability in number of reads, polymorphic loci and SNPs between individuals for both species was observed, while transfer between wild and reared parasite population was more enhanced in case of the isopod. [Conclusion]: The results provide a baseline for the development of new ecological and epidemiological measures for mitigation of two parasites, as the observed transfer seems to be highly conditioned by parasite and environment traits