Morphometric, gametic and parasitological data of clam Ameghynomia antiqua and DNAmt sequences of parasite

The clam Ameghynomia antiqua is a highly important resource for
fisheries due to its high catches volume. It is the bivalve mollusk with
the highest fisheries landings from natural beds on the Pacific coast of
southern South America; however, studies of the reproductive conditions of
this species are scarce and date back many years. The object of the
present work was to evaluate the reproductive characteristics of the
species, analysing its gametogenic and gonadal cycle, and reproductive
indices, in fishery locations that present the natural beds with the
highest fisheries catches, as well as parasite loads in the species. The
gonads of the individuals were sampled monthly over a year and classified
into one of three states called: “in development”, “ripe” and
“spawned”. Synchrony between the sexes was observed in the
indicators of the Gonadosomatic Index and Condition Index in each of the
locations, although no synchrony was observed between locations. In the
gametogenic cycle, the "ripe" state was observed in females in
spring-summer, followed by rapid recovery to new development of the
gonads; in males the "ripe" state was observed throughout the
year. It was observed that males entered the “spawned” state one month
ahead of females. The presence of digenean parasites in the state of
metacercariae was detected in the gonads and mantle. No significant
differences were found in the prevalence or intensity of infection when
analysed by sex and month. The metacercariae were identified, by
sequencing of three DNA regions, as belonging to the clade shared by
species of the genus Parvatrema and close to
the Gymnophalloides; both these genera belong to the family
Gymnophallidae of the superclass Digenea. Infection was observed to reduce
the gonadal tissue, in some cases causing castration. This is the first
record of the presence of these parasites of A. antiqua, with
genetic identification at genus level. These results are relevant for act
proper management of this resource, which is important for fishing.