Abstract
The gill monogenean
Sparicotyle chrysophrii
(Van Beneden & Hesse, 1863) Mamaev, 1984 is a specific and common parasite of wild and cultured gilthead sea bream
Sparus aurata
Linnaeus, 1758, able to cause disease and mortality in aquaculture systems. Few molecular studies have been carried out on this monogenean, and its population structure and genetic diversity are barely known. This study provides the first contribution to the population genetic variation of
S. chrysophrii
, based on two molecular markers - the structural ribosomal RNA (rRNA) for the large subunit (28S) and the cytochrome c oxidase subunit I (COI) gene. Samples were collected from the gills of farmed and wild
S. aurata
from Italy and the Spanish Mediterranean. The analysis included previously published sequences. The 28S rDNA analysis was consistent with previous studies of specimens isolated from
S. aurata
and confirmed the presence of only one species on the gills of this host in the Mediterranean Sea. The COI sequences analysis suggested that the samples isolated in a previous study from a different host species, wild
Boops boops
(Linnaeus, 1758) in the Adriatic Sea, may represent a new undescribed sister species of
S. chrysophrii
. The low nucleotide diversity of
S. chrysophrii
isolated only from
S. aurata
versus the high haplotype diversity revealed small differences between haplotypes. The haplotypes shared between wild and farmed hosts from Spain provided the first molecular evidence of the possible transfer of
S. chrysophrii
between wild and farmed populations of
S. aurata
. The mtDNA COI analysis did not show a clear genetic structure, probably the result of several factors including coevolution, wild and farmed host interactions, and host population structure in space and time.