Factors influencing survival and growth of cultured sandfish, Holothuria sc
abra, 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 average
d 34.4% (+/- 1.2 s.e., n = 4) if juveniles were reared on plates, but was l
ower 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- an
d 140-l tanks indicated it was better to delay transfer to sand until the j
uveniles 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 wh
ich light was reduced by shading indicated that diatoms and epiphytic algae
were important sources of food for cultured juveniles up to 50 mm in lengt
h. However, addition of powdered algae did not improve growth or survival e
xcept at high densities. Growth of juveniles > 20 mm was highly variable an
d 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 da
y(-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.). G
rowth 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 bei
ng held at higher densities subsequently grew at the same rate as juveniles
that were not stunted, when they were reared at lower densities. We conclu
de 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 s
hould 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
.