Increasing the growth of juvenile Pacific oysters Crassostrea gigas by supplementary feeding with microalgal and dried diets

Abstract

Growth rates of juvenile Pacific oysters Crassostrea gigas were studied at a nursery at Pipe Clay Lagoon, Australia, between 1992 and 1997. The highest rates were between December 1992 and May 1993 (instantaneous growth rate, k = 0.020 ± 0.011 day−1), and the lowest rates occurred between January and June 1997 (0.003 ± 0.023 day−1). The latter coincided with lower chlorophyll a concentrations (0.43 μg L−1) than in previous production seasons (0.86–1.5 μg L−1). Supplementary feeding of oysters with Isochrysis sp. (T-ISO) improved k by at least twofold. Two experiments assessed growth with different stocking volumes and diet presentation. Another established that AlgaMac 2000 and Microfeast MB-30 were effective supplementary diets (k = 0.024 and 0.032 day−1 respectively; k = 0.009 day−1 for control), although not as effective as Isochrysis sp. (T-ISO; k = 0.054). The final experiment established a relationship between k and supplementary feed concentrations. A preliminary assessment at Pipe Clay Lagoon – a site with low and variable productivity – indicates that supplementary feeding would be cost-effective. Moreover, it may be necessary if the nursery is to have a continuity of oyster seed supply to service the needs of industry.