Use of premature New Zealand dredge oyster Tiostrea lutaria Hutton larvae for spat production

The New Zealand dredge oyster Tiostrea lutaria Hutton is an incubatory ostreid species that produces fully developed pediveliger larvae, which typically settle shortly after release from the parent. Broods of larvae obtained by opening incubating oysters provide a potential method of spat production, but only a small proportion of the broods obtained in this way are the late‐stage, ready‐to‐settle pediveligers. The majority of the broods are gastrula‐, trochophore‐ and veliger‐stage larvae. Experiments were undertaken to determine whether these early stages, as well as the pediveliger stage, could be reared through to settlement, and so make spat production based on opening incubating oysters much more efficient. Experiments conducted at three temperatures (ambient, ambient + 3 °C and ambient + 6 °C) and under three food regimes (with and without cultured microalgae and without dissolved organics) were unsuccessful in ex‐parent rearing of early larvae (gastrulae and trochophores). Later stage larvae, both veligers and pediveligers, were successfully reared, and high (> 75%) but variable levels of settlement were achieved. Ex‐parent rearing did not benefit from elevated temperatures or the presence of food, and settlement of spat from these prematurely released larvae may be reduced in the presence of food. The ability to rear veliger larvae, as well as pediveligers, greatly increases the potential to use the opening of incubating adult oysters during the breeding season as a source of dredge oyster spat.