Éditeur(s) : Natl Shellfisheries Assoc
Résumé : The pearl industry in French Polynesia is based on exploitation of natural stocks of the black-lip pearl oyster (Pinctada margaritifera); it generates an annual turnover of 90 million euros. Improvements in pearl quality need genetic studies to improve the populations. This pearl oyster is a protandric species, where the sex-ratio normally is biased towards males. There is an increasing interest in gender control to find the mechanisms to augment female proportions for management purposes. This review summarizes information on exogenous and endogenous factors regulating gender in this and other bivalves and concludes that P. margaritifera is a protandric hermaphrodite, developing as a male during the first two years and without evidence of an effect from abiotic and biotic factors on gender during this phase. Later, pearl oysters progressively change to females, reaching a sex ratio close to 1:1 in specimens >8 years; at this stage, gender is apparently influenced by environmental parameters, but particularly by stress. Future research should seek to accurately determine the effect of temperature and food on sex ratios. Studies should be performed to characterize genes responsible for expression of gender. The use of hormones is a path that might be explored to influence the gender of pearl oysters.
Journal Of Shellfish Research (0730-8000) (Natl Shellfisheries Assoc), 2011-08 , Vol. 30 , N. 2 , P. 231-240

Droits : info:eu-repo/semantics/openAccess
http://archimer.ifremer.fr/doc/00040/15100/12543.pdf
DOI:10.2983/035.030.0206
http://archimer.ifremer.fr/doc/00040/15100/

Éditeur(s) : HAL CCSD National Shellfisheries Association
Résumé : International audience
Monitoring gonad maturation for protandrous and functional hermaphrodite species such as the giant clam Tridacna maxima is difficult due to the juxtaposition and relative proportion of male and female tissues in the gonad [gonadal sex ratio (GSR)]. Here, the relevance of the widely used gonadosomatic index (GSI) as proxy of giant clam gonad maturation is tested with a large dataset (n ¼ 265). Gonadosomatic index is compared with other indices, namely the proportion of the male part harboring spermatozoids, the proportion of empty oocyte follicles, the mean oocyte diameter, and the oocyte elongation. At gonad scale, high index variability highlighted partial spawning. At individual scale, male and female maturation proxies were contrasted, showing either asynchronous emissions of male and female gametes or contrasted spermatogenesis and oogenesis duration. The GSI was mostly driven by the number and diameter of oocytes and therefore it is recommended here as primary proxy for female maturity. Except for the oocyte elongation, all indices were affected by the GSR, which ruled out drawing conclusions at population scale. These results highlight the need for maturation stage proxies that are optimized for functional hermaphrodite species.
ISSN: 0730-8000

hal-01613648
https://hal.archives-ouvertes.fr/hal-01613648
https://hal.archives-ouvertes.fr/hal-01613648/document
https://hal.archives-ouvertes.fr/hal-01613648/file/Gaertner-Mazouni-2016-eio.pdf
DOI : 10.2983/035.035.0107

Éditeur(s) : HAL CCSD Station Biologique
Résumé : International audience
From fish samplings (rotenone: 6 February 2002 & 13 May 2003; boxtraps: January 2008 to July 2009) in amangrove lagoon, the demographic structure, reproductive period and diet of Lophogobius cyprinoides were studied.Individual fish were measured (< 1 mm), weighed (± 0.01 g), and sexed by observing the urogenital papilla, sex-ratios andtotal length (TL)-standard length and length-mass relationships were calculated. Five individuals per size class (2 mm) wereused to study sexual maturity by macroscopic observation of gonad structure with a sexual maturity scale, and diet byqualitative and quantitative examination of digestive tract contents and calculation of the following indices: levels offullness and vacuity; occurrence, number, and point frequencies of various food items, and quality of nutrition. Growth isisometric and sexual dimorphism in favor of males (78 vs. 64 mm), demographic structure (18 ≤ TL ≤ 78 mm) and conditionevolved over time, with a distinct femininization of the population. Sexual inversion appeared from 46 mm onward, andtotal masculinization at 72 mm. Protogynous hermaphrodism is advantageous in a sedentary, subcryptobenthic species thatis reproductively active almost throughout the year. The species has an omnivorous diet specialized in copepods and plants
ISSN: 0007-9723

hal-00746079
https://hal.univ-antilles.fr/hal-00746079

Éditeur(s) : HAL CCSD Society of Environmental Toxicology and Chemistry Press (SETAC)
Résumé : International audience
Tributyltin (TBT) and triphenyltin (TPT) are emblematic endocrine disruptors, which have been mostly studied in gonochoric prosobranchs. Although both compounds can simultaneously occur in the environment, they have mainly been tested separately for their effects on snail reproduction. Because large discrepancies in experimental conditions occurred in these tests, the present study aimed to compare the relative toxicity of TBT and TPT under similar laboratory conditions in the range of 0 ng Sn/L to 600 ng Sn/L. Tests were performed on the simultaneous hermaphrodite Lymnaea stagnalis, a freshwater snail in which effects of TPT were unknown. Survival, shell length, and reproduction were monitored in a 21-d semistatic test. Frequency of abnormal eggs was assessed as an additional endpoint. Triphenyltin hampered survival while TBT did not. Major effects on shell solidity and reproduction were observed for both compounds, reproductive outputs being more severely hampered by TBT than by TPT. Considering the frequency of abnormal eggs allowed increasing test sensitivity, because snail responses to TBT could be detected at concentrations as low as 19 ng Sn/L. However, the putative mode of action of the 2 compounds could not be deduced from the structure of the molecules or from the response of apical endpoints. Sensitivity of L. stagnalis to TBT and TPT was compared with the sensitivity of prosobranch mollusks with different habitats and different reproductive strategies.
Environmental Toxicology and Chemistry

hal-00877955
https://hal.archives-ouvertes.fr/hal-00877955
DOI : 10.1002/etc.2200
PUBMED : 23450754

Éditeur(s) : Elsevier
Résumé : The gametogenic cycle and the reproductive effort of the blacklip pearl oyster, Pinctada margaritifera, cultivated in Takapoto lagoon were studied for a 1-year period (March 1997-April 1998) by bimonthly observations of gonadal sections, dry tissue weights and gonadal index in a population of pearl oyster composed of three age-groups. pearl oysters attained sexual maturity in the end of their first year (height approximate to 40 mm), implying that P. margaritifera is a late-maturing species in comparison with other Pteriidae. This species was also confirmed to be a marked protandrous successive hermaphrodite in culture, with 100 % of males at first maturity and 75 % in older pearl oyster (height > 120 mm). The general pattern of gametogenic activity, fairly synchronous in both sexes, was comparable with that of other tropical bivalves: reproduction occurs continuously throughout the year with a maximal activity during the warm season (November-May). No resting period was observed. Quantitative growth data showed that P. margaritifera exhibits an annual synchronised polymodal spawning pattern, with two spawning peaks in age-group I (height approximate to 70 mm) and five in age-groups II (height approximate to 100 mm) and III (height approximate to 120 mm). Spawning was sometimes incomplete, nevertheless a clear relationship between gamete production (P-R, g) and size (height H, mm) was obtained: P-R = 5.26 x 10(-7) H-2.91 (R-2 = 0.99, p < 0.05). Estimation of P-R was used to calculate the annual reproductive effort in P. margaritifera. Reproductive effort (%) was similar to those calculated for temperate species and showed a progressive increase with the age of pearl oyster, from 7 % in age-group I to 38 % in age-group III. This study showed that, in a fairly stable tropical environment such as the Takapoto lagoon, P. margaritifera is a multiple spawner, which uses an opportunistic reproductive strategy, allowing investment all year around, of any surplus energy into gamete production. Surplus energy is ensured by the high pumping rates developed by this non-symbiotic bivalve to succeed in low seston conditions. (C) 2000 Ifremer/Cnrs/Inra/Ird/Cemagref/Editions scientifiques et medicales Elsevier SAS.
Le cycle et l'effort de reproduction de l'huître perlière à lèvres noires, Pinctada margaritifera, cultivée dans le lagon de Takapoto, ont été étudiés sur une période annuelle (de mars 1997 à avril 1998), par un suivi bimensuel des stades de maturation et des indices gonadiques, sur une population en élevage composée de trois groupes d'âge (1, 2 et 3 ans). Cette étude a confirmé que P. margaritifera est une espèce qui se reproduit tardivement par rapport aux autres Ptériidés (elle atteint sa maturité sexuelle à la fin de sa première année, pour une hauteur approximative de 40 mm). Par ailleurs, elle présente, en élevage, une protandrie marquée (100 % de mâles à première maturité, 75 % pour des huîtres âgées de trois ans). Le schéma général de sa gamétogenèse, relativement synchrone dans les deux sexes, est comparable à celui des autres bivalves tropicaux : la reproduction est quasiment continue (aucune période de repos sexuel) avec une activité accrue en saison chaude (de novembre à mai). L'analyse des variations du poids de la gonade suggère l'existence de deux pics d'émission de gamètes chez les huîtres de un an et cinq pics chez les huîtres de 2 et 3 ans (cycle de reproduction de type polymodal). Bien que ces émissions de gamètes soient parfois incomplètes, une relation entre la production de gamètes (PR, en g) et la taille de l'huître perlière (hauteur, H, en mm) a été établie : PR = 5,26 x 10-7 H2,91 (R2 = 0,99, p < 0,05). Ces résultats ont permis de calculer l'effort de reproduction de P. margaritifera à Takapoto et sur un bilan annuel : il augmente avec l'âge de l'huître perlière de 7 % pour le groupe d'âge I à 38% pour le groupe d'âge III. Ces valeurs annuelles sont similaires à celles calculées chez les bivalves de milieux tempérés. Cette étude a donc montré que, dans un environnement tropical assez stable tel que celui du lagon de Takapoto, P. margaritifera présente une reproduction continue, avec plusieurs pics d'émission de gamètes par an. Cette stratégie « opportuniste » permet l'investissement, de tout surplus d'énergie en production de gamètes, tout au long de l'année. Malgré la faible concentration du milieu en nourriture, ces surplus d'énergie sont assurés par les fortes capacités de filtration développées par cette espèce tropicale non-symbiotique.
Aquatic Living Resources (0990-7440) (Elsevier), 2000 , Vol. 13 , N. 1 , P. 37-48

Droits : 2000 Ifremer/Cnrs/Inra/Ird/Cemagref/Éditions scientifiques et médicales Elsevier SAS
http://archimer.ifremer.fr/doc/2000/publication-1391.pdf
DOI:10.1016/S0990-7440(00)00135-2
http://archimer.ifremer.fr/doc/00000/1391/