Survival and growth of cultured juvenile sea cucumbers, Holothuria scabra

Factors influencing survival and growth of cultured sandfish, Holothuria scabra, were evaluated in a series of experiments in land-based nursery tanks. There was a critical period in the culture of newly-settled juveniles (< 5 mm) during which high mortality occurred. After 1 month, survival averaged 34.4% (+/- 1.2 s.e., n = 4) if juveniles were reared on plates, but was lower and more variable if they were detached and reared on hard substrates. On plates, juveniles grew to a mean size of 13 mm in length (range 3 to 41 mm) after 1 month. An experiment in small aquaria showed that juveniles as small as 3 mm could be transferred to sand. However, experiments in 70- and 140-l tanks indicated it was better to delay transfer to sand until the juveniles reached a size of 20 mm and 1 g. Survival of H. scabra > 20 mm was high: mortality was < 4% over 2 months, and restricted to tanks stocked at high density, or with reduced light. Juveniles reared on sand appeared to feed both on sand and off the hard surfaces of the tanks. Experiments in which light was reduced by shading indicated that diatoms and epiphytic algae were important sources of food for cultured juveniles up to 50 mm in length. However, addition of powdered algae did not improve growth or survival except at high densities. Growth of juveniles > 20 mm was highly variable and density-dependent: coefficients of variation averaged 25.8% (+/- 2.2 s.e.). Absolute daily growth rates for juveniles stocked at 20 to 31 mm, ranged from a mean of 0.2 to 0.8 mm day(-1), with an overall average of 0.5 mm day(-1) (+/- 0.03 s.e.) over 2 months. This was equivalent to a weight range of 0.1 to 0.4 g day(-1), and an average of 0.2 g day(-1) (+/- 0.02 s.e.). Growth in H. scabra slowed when densities reached approximately 225 g m(-2), i.e., when individuals averaged 40 g. Juveniles stunted as a result of being held at higher densities subsequently grew at the same rate as juveniles that were not stunted, when they were reared at lower densities. We conclude that it is possible to rear newly-settled H. scabra in land-based tanks using simple technology and little or no added feeds. Consequently, there should be no major impediment to the large-scale production of juveniles for stock enhancement programs provided they can be released successfully at a size of 60 mm and 20 g. (C) 1999 Elsevier Science B.V. All rights reserved.