Factors influencing the capacity for pediveliger larvae of the giant clam, Tridacna noae, to ingest and digest cells of microalgae concentrates

Abstract

Veliger larvae of giant clams are demonstrable planktotrophs and provision of a particulate food source is generally accepted to improve hatchery production. However, the appropriateness of continuing to administer particulate food after larvae settle and develop as pediveligers is unclear. This study evaluated whether larval (age and size) and microalgal (species and cell density) factors influenced the capacity for pediveligers of Tridacna noae to ingest and digest cells from commercially available microalgae concentrates. Pediveligers at 6 and 10-days post-fertilisation were offered one of four microalgae species (Isochrysis sp., Pavlova sp., Tetraselmis sp., Thalassiosira weissflogii) at two cell densities (4000 and 8000 cells mL−1) and subsequently examined using epifluorescence microscopy. The appropriateness of continuing to administer microalgae as a food source was found to diminish as pediveligers approached metamorphosis, with negligible ingestion occurring at 10-days post-fertilisation. Earlier in development, at 6-days post-fertilisation, ingestion was significantly influenced by larval size, microalgae species, and microalgae cell density. Considering capacity for both ingestion and digestion, the Isochrysis sp. and Tetraselmis sp. microalgae concentrates had the greatest potential as a particulate food source for pediveligers of T. noae. The results of this study provide a basis for further refinement of giant clam hatchery procedures utilising microalgae concentrates as a larval food source.