Optimising the delivery of the key dietary diatom Chaetoceros calcitrans to intensively cultured Greenshella'[cent mussel larvae, Perna canaliculus

摘要

The diatom Chaetoceros calcitrans forma pumilum is an important dietary component for cultured Greenshella"[cent mussel larvae, Perna canaliculus. However concerns surrounding potentially deleterious side effects have motivated a series of experimental trials to optimise the safe usage of this alga. Bioassays involved raising veliger larvae in the purpose-built Cawthron Ultra-Density Larval rearing (CUDL) system; an array of 2.5-L tanks were stocked with 2-day-old veligers (200larvaemLa degree 1) supplied with inflowing water dosed with sufficient microalgae to maintain a fixed concentration of cells, after compensating for ingestion. The nutritional role of C. a~calcitrans' was examined by adjusting its cellular fraction in the feed environment. Diets of 0, 5, 66, 95 and 100% C. a~calcitrans' were each offered to six replicate rearing tanks, using Isochrysis aff. galbana (T-Iso clone) to maintain a total of 40cellsI14La degree 1 in the larval cultures. The 66% C. a~calcitrans' diet was also offered at 3, 20, 60 and 120cellsA mu La degree 1 (n =6). Higher C. a~calcitrans' fractions sustained faster growth, with 95% and 100% treatments producing 23-day-old pediveligers of 240A plus or minus 15I14m and 228A plus or minus 5I14m mean shell length, respectively; compared to 212A plus or minus 7I14m in the 66% treatment (40cellsI14La degree 1). However, high C. a~calcitrans' treatments were more volatile, had higher mortality and greater predisposition towards population crashes. Similarly, reduced survival was observed in the high feed treatment of 120cellsA mu La degree 1, reflected in a final pediveliger yield of 29A plus or minus 6%, compared to 47A plus or minus 3% at 60cellsA mu La degree 1 and 36A plus or minus 7% at 40cellsA mu La degree 1. The 5% C. a~calcitrans' and 20cellsA mu La degree 1 treatments showed signs of nutrient limitation, while larvae fed 0% C. a~calcitrans' or a total of 3cellsA mu La degree 1 starved, failing to reach metamorphosis. A standard diet consisting of 66% C. a~calcitrans' and 34% I. aff. galbana maintained at 40cellsI14La degree 1 was used to test the hypothesis that culture age increased deleterious side effects associated with feeding C. a~calcitrans'. The final stage of batch culture, using 20-L nylon carboys inoculated with 1010 C. a~calcitrans' cells was allowed to age for 2, 3, 4, 5 or 6days before being fed to larvae. After 21days eating 2-day-old C. a~calcitrans' larvae reached a mean shell length of 236I14m, were eating 35,000 cells larvaa degree 1 daya degree 1, and had a survival rate of 59A plus or minus 3%; in contrast, larvae eating 6-day-old cells only reached 214A mu m, eating 17,000 cells larvaa degree 1 daya degree 1, with an overall survival of 46A plus or minus 7%. While C. a~calcitrans' is valuable in the larval culture of P. canaliculus and many other bivalves, appropriate feeding protocols are needed when using this diatom.