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. 2022 Apr 8;17(4):e0266538.
doi: 10.1371/journal.pone.0266538. eCollection 2022.

Gonadal cycle, reproductive indices and detection of parasitism in the clam Ameghinomya antiqua in natural beds of importance for fisheries

Roberto Jaramillo  1 , Valentina Prida  2 , Pedro S Rubilar  3 , Leyla Cardenas  4   5 , Valeria Prieto  4 , Marcela P Astorga  2
Affiliations

Gonadal cycle, reproductive indices and detection of parasitism in the clam Ameghinomya antiqua in natural beds of importance for fisheries

Roberto Jaramillo et al. PLoS One. .

Abstract

The clam Ameghynomia antiqua is a highly important resource for fisheries due to its high catches volume. It is the bivalve mollusc 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.

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Conflict of interest statement

The authors have declared that no competing interests exist.

Figures

Fig 1
Fig 1. Monthly variation of the Gonadosomatic Index (GSI) and Relative Condition Index (RCI) of the chilean clam A. antiqua in natural beds.
(A) Gonadosomatic Index in natural beds at Carelmapu. (B) Gonadosomatic Index in natural beds at Quellón. (C) Relative Condition Index in Carelmapu. (D) Relative Condition Index in Quellón. The error bars correspond to standard error.
Fig 2
Fig 2. Microphotographs of gonadal states of A. antiqua.
(A) "in development" female; (B) "ripe" female; (C) "spawned" female; (D) "in development" male; (E) "ripe" male; (F) "spawned" male. Microphotographs of cross sections of testicle and ovary stained with HE (1000X). Fw: follicular wall; spd: spermatids; Spz: spermatozoa; rspz: remains of spermatozoa; lu: lumen; eo: early oocytes; go: growing oocytes; mo: mature oocytes; do: deteriorating oocytes.
Fig 3
Fig 3. Temporal variation in the state of maturity in clams A. antiqua.
(A) State of maturity of females at Carelmapu locality. (B) State of maturity of males at Carelmapu. (C) State of maturity of females at Quellón locality. (D) State of maturity of males at Quellón.
Fig 4
Fig 4. Parasites belong to the family Gymnophallidae collected from the clam A. antiqua.
(A). Mantle tissue parasitized by the state of metacercariae observed with stereoscopic microscope at 1.5X. (B). Parasites recovered from the gonad tissue observed at 2.0X. (C). Photomicrograph of a gonadal section of a male with a high degree of parasitism, the indicated area shows segments of parasites located within one of the gonadal tubules. (D). Individual of Gymnophallid digenean observed with 40X (scale bar 40 μm).
Fig 5
Fig 5. Phylogenetic reconstruction by NJ based on the ITS-2 region, for parasites collected from A. antiqua.
The numbers along the branches indicate the percentages of the bootstrap support values resulting from the analyses of NJ. Codes indicate accession numbers for samples obtained from the GenBank.
See this image and copyright information in PMC

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