Developing a hatchery-based aquaculture of tropical rock oysters provides opportunities for likelihood diversification in developing countries. In the Indo-Pacific region, several species stand out as promising candidates for modern hatchery production programs, particularly Saccostrea cucullata and S. echinata. However, no formal studies have compared the productivity of these species, despite the importance of this information for effective resource management and planning. Our study aimed to produce both species in the hatchery, and compare their growth performance during key phases of the production process (larval, nursery, and grow-out).
Broodstock oysters collected from two sites were identified using multiplex PCR tests based on COI mitochondrial primers. Batch spawning was triggered by a mix of desiccation and thermal stress. During the larval phase we monitored growth and development. Competent larvae settled on oyster-shell cultch, and were subsequently transferred to nursery raceways for a period of one year. Growth during the nursery phase was followed for 98 days under two conditions: (1) raceways provided with microalgae produced in the laboratory, and (2) upwelling cylinder sieves provided with seawater from an earth pond maintained with ‘semi-natural’ microalgae blooms. To compare performance during the grow-out phase, animals were placed in baskets and deployed across three sites capturing a gradient in food availability: (1) Vairao Lagoon (nutrient-poor), (2) Phaeton Bay (natural, nutrient-rich), and (3) earth pond (managed, nutrient-rich). After two months, we recorded growth and survival as a function of species and grow-out site.
We completed the reproduction of S. cucullata and S. echinata, with fertilization rates higher than 90%. Results showed that S. echinata consistently outcompetes S. cucullata. S. echinata larvae grew faster and developed earlier than S. cucullata (Fig. 1A). S. echinata was more productive in the nursery, though independently of the growth system used (Fig. 1B). Grow-out trials also revealed higher growth rates for S. echinata, but only in nutrient-rich sites (Fig. 1C). Survival was lower at the natural, nutrient rich site, likely due to fouling (Fig. 1D). Finally, S. cucullata invests more energy into reproduction, suggesting a possible mechanism to explain the differences in growth.