Substrate preference for burying and feeding of sandfish Holothuria scabra juveniles

Substrate preference for both burying and feeding of sandfish Holothuria scabra juveniles (3–6 g wet body weight) and their associated daily behavior, growth and survival were investigated in laboratory and field experiments using different coastal substrate types (silty mud, sandy mud, and coarse sand) to determine the ideal habitat for potential grow-out culture, sea ranching or stock enhancement of this important sea cucumber species. During the peak hours of burying (03:00–09:00 h) and feeding (15:00–03:00 h), a significantly greater number of sandfish juveniles preferred to bury in (28.3%) and feed on (21.5%) sandy mud, typical of intertidal coastal sand flats. Silty mud was the least preferred substrate for feeding (13.5%) and burying (13.8%). Burying and feeding preferences of sandfish juveniles were not significantly influenced by the presence of seagrass (Thalassia hemprichii) on coarse sand. Growth of sandfish juveniles in the first two weeks of rearing in tanks was significantly greater on coarse sand (growth rate: 0.59 g d⁻¹ or 7.0% d⁻¹), followed by sandy mud (0.34 g d⁻¹ or 4.72% d⁻¹) while OM content of these sediments remain almost unchanged. On silty mud, sandfish juveniles constantly shrunk (−0.02 g d⁻¹ or −0.63% d⁻¹) for 8 weeks while sediment OM content increased. In the field, silty mud substrate of a mangrove pond caused total mortality of sandfish within two weeks, while sandy mud substrate of a sand flat provided significantly higher growth than the control (no sediment), but not significantly different than coarse sand of a seagrass bed. Sandy mud to coarse sand substrates of intertidal sand flats were most preferred by sandfish juveniles while silty mud associated with muddy mangroves and culture ponds seems to be unsuitable that sandfish would opt to avoid. Our results will contribute to the selection of suitable sites for sandfish sea ranching and stock enhancement in coastal areas.