The Effect of Sediment Quality and Stocking Density on Survival and Growth of the Sea Cucumber Holothuria scabra Reared in Nursery Ponds and Sea Pens

Abstract

The effect of sediment quality and stocking density on the survival and growth of the sea cucumber Holothuria scabra reared in nursery ponds and in pens was studied at Aqua-Lab Farm in Toliara, south west Madagascar. Three types of sediment (micro-atoll, mangrove and seagrass bed) were tested for their food quality properties. Experiments were carried out in ponds at juvenile stocking densities of 10, 20, 30 and 40 individuals m^-2 (juveniles size: 0.24 to 15 g) and in sea pens at juvenile stocking densities of 3, 6, 9 and 12 individuals m^-2 (juveniles size: > 15 g). The results showed that the nature of the sediment did not affect the survival or growth of H. scabra. High survival (>95 %) and good growth rates (>0.22 g d^-1) were observed during eight weeks of rearing in ponds. However, stocking density clearly influenced its growth. Highest growth rates of 0.23 g d^-1 and 0.64 g d^-1 were respectively obtained at low stocking densities in the ponds (stocking density: 10 individuals msup>-2; rearing time: 10 weeks) and sea pens (stocking density: 3 individuals m^-2; rearing time: 9 months). Regardless of stocking density, juvenile growth ceased above a maximum biomass of 160 g m^-2 in outdoor ponds and 692 g m^-2 in sea pens. In order to optimize the farming of H. scabra, we suggest (i) the use of sediment collected from seagrass beds for nursery ponds, although sediments from other sources may be used, and (ii) the stocking biomass should not exceed 160 g m^-2 in nursery ponds and 650 g m^-2 in sea pens or at natural ranching sites.

Keywords: Holothuria scabra, endobenthic sea cucumber juveniles, rearing, survival, growth.