Effect of different nucleus sizes and culture duration on the quality of half pearls (MAB ' E) produced by the winged pearl oyster Pteria sterna (Gould, 1851) in Ecuador

This study aims to evaluate the influence of nucleus size and culture duration on the nacre deposition rates of half pearls produced by the winged oyster P. sterna. For the nucleus size study, three different sizes of hemispherical implants were tested; small (9 mm), medium (11 mm) and large (14 mm), each of these treatments was assigned three baskets, containing 7 oysters each (for a total of 21 oysters), while an additional 21 individuals were kept without implants as a control treatment. All groups were cultured for six months. At the end of this experimental period, the shell length, shell height, and shell thickness growth of the oysters implanted with the small and medium-sized nuclei were significantly higher than that of the oysters with large nuclei. However, significantly higher nacre deposition rates were observed in the oysters with large nuclei. Mortality reached only 2% in all treatments, and the results show a lower proportion of good quality hemispherical pearls (23.0%) in the oysters implanted with a large nucleus, while for those implanted with small and medium nuclei the percentage of good quality half pearls reached 71.4% and 69.8%, respectively. Regarding the annual nacre deposition study, three replicates were sampled monthly, along with the environmental variables of the site used, to examine the influence of these variables on their nacre deposition rates. Results showed that, in just 8 months of culture, nacre thickness exceeded the average of 1.0 mm. A principal component analysis (PCA) showed a direct and significant relationship between instantaneous nacre deposition rate (k), water temperature, and food variables. These results demonstrate the potential for the winged oyster P. sterna for the development of a productive alternative for aquaculture in Ecuador.