Variations in the reproductive cycle of the oyster Crassostrea virginica (Gmelin, 1791), Pueblo Viejo lagoon, Veracruz, Mexico

Abstract

1 - Mexican oyster production in the Gulf of Mexico has fallen drastically in most coastal lagoons, whereas Pueblo Viejo Lagoon production (state of Veracruz) has been sustained, providing a source of seed for the restocking of other lagoons. This has been achieved due to bed management carried out by local fishermen. This management is based on empirical knowledge of seed collection from planted shell beds. 2 - This study describes variations in gametogenic activity and the reproductive cycle during the year 2002, with a view to improving shell laying programs. Samples were taken from two beds, subject to different environmental and pollution conditions. Malagana point, with a heavy organic load and a strong tidal current, and Matacuaya Island, with a low organic load and no current. 3 - Thirty oysters over 8 cm shell length were sampled monthly from each bed for histological analysis of the gonad tissue. 4 - There were variations in gonad activity between localities, which are reflected in the gametogenic cycle and spawning. At both stations spawning extends throughout the year, but in larger numbers from June to October at Malagana, contrasting with a low frequency for most of the year and one intense spawn during July and August at Matacuaya. 5 - These differences in the gametogenic cycles and spawning periods are a result of population recovery capacities under different environmental conditions. The Malagana population is exposed to a higher organic load from the Panuco River in addition to urban discharge, resulting in shorter post-spawn and rest periods, faster gametogenesis, and a well defined mature stage with a high intensity spawning period and three peaks. Meanwhile, the oyster population from Matacuaya presented longer, more intense post-spawn and rest stages; gametogenesis extended longer, in a lower percentage of the population, with a brief maturity period. 6 - This differential reproductive behaviour has positive implications in recruitment, giving the oyster populations from Pueblo Viejo lagoon the opportunity to take advantage of every settlement possibility throughout the year. However, the higher organic load that enhances reproduction at Malagana poses a health risk, given the high fecal bacteria count and heavy metal concentration in the sediment, constantly re-suspended by the tidal current flux.