Gametogenetic cycle and reproductive effort assessed by two methods in 3 age classes of Pacific oysters, Crassostrea gigas, reared in Normandy

Abstract

Two methods were used to estimate the reproductive output of female Pacific oysters reared in Normandy: histology with image analysis and ELISA (Enzyme-Linked ImmunoSorbent Assay) which allowed the quantification of egg protein. Condition indices, gonad area and gametogenetic stages of the oysters were determined in the entire population (males and females) between May and October 2005. All investigations were performed in 3 age classes: oysters in their first, second or third years (corresponding to spat, half-grown and market-sized oysters, respectively). Both quantitative histology and ELISA provided similar results in terms of reproductive effort (illustrated by the gonado-somatic index, GSI) except during the GSI drop, corresponding to spawning, which was less marked with the ELISA method. Growth depended on oyster age, the sex ratio was well balanced and the reproductive cycle was synchronized in all age classes. In the 3 age classes, most of the oysters were ripe and ready to spawn on August 8, and ten days after the post-spawning stage was observed in 40% of spat oysters and 70% of half-grown and market-sized bivalves. The major difference between age classes was observed in the reproductive investment, with spat having a lower reproductive output. For example, in males and females, the gonad area reached 78-79% in the median animal section at full maturity (August 8) in half-grown and marketable oysters while it attained only 59% in spat. At the same time, GSI in females was, respectively in spat and the 2 oldest age classes, 33% (quantitative histology)-36% (ELISA) and 55% (quantitative histology)-60% (ELISA). The mean assessed gonad weight and fecundities increased with the age of the oysters: 1.3 g and 12 million eggs, 7.8 g and 135 million eggs, and 11.5 g and 146 million eggs in spat, half-grown and market-sized oysters, respectively. Marked differences thus appear between 2 and 3-year-old oysters and spat. As early as their first reproductive cycle, the young oysters not only showed the reproductive features of the species in Normandy, but also a pronounced lower reproductive effort. This lower energy demand could explain their higher survival rate.

Effects of Alexandrium minutum exposure upon physiological and hematological variables of diploid and triploid oysters, Crassostrea gigas

“…Relationships between food quality and quantity, energy storage, and reproduction are now well established in C. gigas (Soudant et al, 1999;Berthelin et al, 2000;Royer et al, 2008;Rico-Villa et al, 2009). These observations suggest that HAB exposure, by affecting nutrition-related functions, may impact reproduction processes and gamete output.…”

Variación del ciclo gonádico del ostión americano, Crassostrea virginica (Ostreoida: Ostreidae) en función de su talla en la laguna de Tamiahua, Veracruz, México

“…En el trabajo de Pazos, Román, Acosta, Abad & Sánchez (1996) se evaluó el efecto de la talla Mytilus edulis sobre sus estadios gonádicos, reportando que los individuos juveniles mostraron un solo periodo de liberación anual, mientras que los adultos liberaron en dos ocasiones. En contraste, Royer et al (2008) al estudiar el desarrollo de la madurez gonadal en tres clases de tallas para Crassostrea gigas, reportaron que su ciclo reproductivo no presentó diferencia en función de la talla del ostión. En este mismo sentido, Quayle (1969) sugiere que el inicio en la actividad reproductiva en Crassostrea gigas, está más relacionado con factores ambientales (temperatura, salinidad, pluviometría, corrientes y alimento disponible) que con la misma talla del ostión.…”

Disruption of amylase genes by RNA interference affects reproduction in the Pacific oyster Crassostrea gigas

“…On examining the median part of the visceral mass, Royer et al (2008) found the percentage surface occupied by the gonad to be directly linked to the number and/or size of gametes produced and therefore representative of reproductive effort, which is linked to the proportion of energy allocated to reproduction (Todd and Havenhand, 1983;Normand et al, 2009). In the DEB theory, oyster reproductive effort was found to depend mostly on the halfsaturation coefficient for ingestion (Bernard et al, 2011).…”

“…For each sample, a 3 mm crosssection of the visceral mass was excised in front of the pericardic region and immediately fixed in modified Davidson's solution at 4°C for 48 h. In order to avoid any bias related to the cut of the median section through the visceral mass, these cuts were always made at the same position by the same person and the same manner (Royer et al, 2008). Sections were dehydrated in ascending ethanol solutions, cleared with the xylene substitute Microclearing (Diapath, Italy), and embedded in paraffin wax.…”