Role of sand as substrate and dietary component for juvenile sea cucumber Holothuria scabra

The sea cucumber Holothuria scabra, or sandfish, is a commercially valuable aquaculture species; however viable intensive tank-based aquaculture techniques have not yet been developed. This study aimed to assess the role of sand as a substrate and/or dietary component in the intensive tank culture of sandfish in recirculating aquaculture systems (RAS) in South Africa. A control experiment was conducted to confirm the reported positive effect of sand as a substrate on sandfish growth and a sand-in-diet experiment was conducted to determine if the incorporation of sand into formulated diets could improve sandfish growth in bare tanks. In the control experiment, the mean growth rate of juvenile sandfish in the bare tanks was significantly lower than that of the juveniles reared in tanks with a sand substrate (-0.12±0.16gday^-1 SE and 0.03±0.01gday^-1 respectively; F_(1,2)=1.91, p<0.001). However in the sand-in-diet experiment, the mean growth rate of juvenile sandfish in bare tanks, fed a formulated diet containing 20% sand was not significantly different to juveniles fed a standard formulated diet (-0.13±0.01 and -0.12±0.16gday^-1 respectively; F_(1,2)=1.26, p>0.05). Results confirmed the reported positive effect on sandfish growth when sand is provided as a substrate, however sand in diets did not promote growth in the same way, indicating that the inclusion of sand in formulated diets is unlikely to compensate for the lack of sand as a substrate. Future research should therefore aim to identify the optimum parameters of sand substrate and develop tank holding systems capable of maintaining favourable substrate conditions for intensive sandfish culture.