Holothuria Scabra Research Articles

Restocking the sea cucumber Holothuria scabra: Sizing no-take zones through individual-based movement modelling

The valuable sea cucumber Holothuria scabra, known as ‘sandfish’, has potential for restocking. However, there is little information available to determine the size of the no-take zones (NTZs) needed to protect the released animals so that they can form nucleus breeding populations. To do this, we measured short-term movement paths of released juvenile (1–105 g) and wild adult (130–690 g) sandfish in a seagrass bed in New Caledonia. We then developed an individual-based model (IBM) to predict long-term dispersal of sandfish released as juveniles (1–16 g) at 1 individual m −2 within a 1-ha area, drawing on distributions of speed and directionality and the relationship between speed and animal weight from field data. Movement was non-random at the sampling scale used, since animals tended to turn <90° at each 2-h time step. We examined high- and low-growth scenarios by applying 50% and 25% of the modelled growth rates of sandfish held in earthen ponds (where they are known to grow faster). The dispersal of released sandfish was predicted to be limited in the first 2 years, then markedly faster thereafter. After 10 years, 6–12% of surviving animals were predicted to remain in the original 1-ha release site. To protect surviving sandfish as nucleus breeding populations for 10 years, and accepting 10% spillover, square NTZs would need to be 19–40 ha. The findings are useful for the management of restocking and pre-defining the size of sites for recapture surveys. Our model allows user-specified values for future releases and should be applicable for other sedentary marine invertebrates where basic data on movement and growth are available.

Efficacy of chemical markers and physical tags for large-scale release of an exploited holothurian

Hatchery-produced juveniles need to be distinguished from wild conspecifics in order to evaluate the success of restocking experiments and stock enhancement. The commercially valuable sea cucumber Holothuria scabra, or ‘sandfish’, has potential for stock enhancement but cheap, long-lasting tags have not yet been developed. We evaluated five non-genetic tags against several criteria: cost, ease of application, retention rate, and ease of detection. In a 1-month trial, T-bar tags and visible elastomer implants proved unsuitable on hatchery-produced sandfish juveniles. Coded-wire tags and two fluorochromes, tetracycline and calcein, showed more promise, so retention rates of these tags were tested on juveniles held in an earthen seawater pond for 1 year. Sixty percent of juveniles retained at least one of two coded-wire tags for 1 year. Under UV illumination, spicules from the body wall of sandfish immersed in solutions of tetracycline are yellow, whereas calcein-stained spicules are green. From months 1 to 12 after immersion, the average percentage of stained spicules declined from 40% to 8% with tetracycline and 54% to 5% with calcein. After 1 year stained spicules were detected in all immersed animals, i.e. mark retention was 100%. Stained spicules from the ventral body wall of juveniles were generally in greater proportions, and fluoresced brighter, than those from the dorsal body wall. Spicule density exceeded 7000 spicules per mm 2 of body wall in juveniles of 2–13 g, and decreased with sandfish weight. Fluorescence provides a simple diagnostic tool for identifying marked individuals and the sampling is non-destructive. Several mm 2 of outer body wall is ample for tag identification. Immersion-staining with fluorochromes is preferred to coded-wire tags and provided a cheap and reliable batch-mark for distinguishing released and wild sandfish.

Experimental evaluation of co-culture of juvenile sea cucumbers, Holothuria scabra (Jaeger), with juvenile blue shrimp, Litopenaeus stylirostris (Stimpson)

The co-culture of juvenile sea cucumber Holothuria scabra (Jaeger), or ‘sandfish’, with juvenile blue shrimp Litopenaeus stylirostris (Stimpson) was tested by growing groups in co-culture and monoculture for 3 weeks in tanks with enriched sand substratum. Feed was supplied on trays, accessible only to shrimp. Survival of shrimp and sandfish was high in all treatments (73–100%). Growth of shrimp did not differ between monoculture and co-culture, but sandfish grew significantly slower in co-culture (P=0.03), although their sand burying and surface foraging were apparently unaffected by shrimp (P=0.76). However, shrimp increased the levels of total ammonia-N in tanks, which related inversely with sandfish growth (P=0.04). Conversely, sandfish did not appear to lower the water quality for shrimp culture. While sandfish bioturbate sediments and eat organic deposits, the juveniles did not significantly reduce the organic content of sand in tanks. Co-culturing juveniles of the two species in earthen ponds appears feasible, with no detriment to shrimp production, presenting a cost-effective method for growing sandfish to larger sizes for restocking. These findings underpin further studies to test the viability of commercial co-culture of sandfish with blue shrimp at later stages in the production cycle of shrimp.

Transportation methods for restocking of juvenile sea cucumber, Holothuria scabra

The sandfish, Holothuria scabra, is a heavily exploited sea cucumber species. Minimising stress in the transportation of hatchery-produced sandfish juveniles to release sites is critical for successful restocking. Replicate groups ( n = 4) of 20 hatchery-produced juveniles (1–5 g) were held in plastic bags with oxygen under 6 transport durations (0, 2, 4, 8, 12 and 24 h), two media (water or saturated sponge), and two temperature regimes (ambient and cool). Subsequent deaths and sand burrowing of the groups in release chambers were monitored for 5 days. Juveniles eviscerated or died only in treatments at ambient temperature on sponge for 24 h. Oxygen consumption in bags was reduced at cool temperature. On the first day after release, the normal sand burrowing was suppressed in juveniles held for 12 and 24 h, suggesting that pre-release acclimation for 1 day at field sites would benefit restocking. After the initial ‘shock’ of transport, handling stress appeared to increase burrowing behaviour for several days. Hatchery-produced sandfish also proved hardy for transport in high densities (100 and 200 juveniles per bag) and transportation stress will be minimised in seawater held at cool, constant temperature.

Natural hybridization does not dissolve species boundaries in commercially important sea cucumbers

The study of species boundaries in areas of sympatry provides important insight into speciation processes. We investigated whether (i) two sympatric holothurians, Holothuria scabra and H. s. var. versicolor constituted species, and (ii) specimens of intermediate phenotype hybrids. Results from allozyme and 16S mtDNA sequence analyses indicated these two sea cucumbers to be distinct but young biological and phylogenetic species. Several private allozyme alleles existed and a Bayesian analysis grouped varieties into separate clusters. MtDNA sequences hardly varied within each taxon, and nine single bp changes were diagnostic between these two taxa. Allozyme allele frequencies in individuals of intermediate phenotype were intermediate to those of H. scabra and H. s. var. versicolor, most private alleles were present and heterozygote frequencies were higher than in either species. Ancestry coefficients modelled for these individuals were close to 0.5, indicating that the two taxa contributed equally to their genome. MtDNA sequences were identical to those of either species. We conclude that individuals of intermediate phenotype represent F1 hybrids. The presence of hybrids demonstrates that the opportunity for introgression exists, but is not realized, as backcrossing and introgression were not supported by the data. Thus, the genetic integrity of either holothurian species remains intact through an unknown postzygotic mechanism, possibly hybrid sterility. © 2005 The Linnean Society of London, Biological Journal of the Linnean Society, 2005, 85, 261‐270.

Destruction of a Holothuria scabra population by overfishing at Abu Rhamada Island in the Red Sea

Populations of Holothuria scabra at Abu Rhamada Island were investigated during 52 months, from July 1999 to October 2003. During the first 23 months (July, 1999-May, 2001) the Island had a robust population with a tri-modal size frequency distribution curve, very high densities (85.7-95.1 ind./100 m2 at the sandy habitat), high abundance (3362-3110 individuals) and biomass (46.7-34.3 kg/100 m2). Also, during this period most individuals were at depths between 4 and 6m and no individuals were recorded deeper than 15m. The population declined after harvesting began (June, 2001) and by March, 2002 the size frequency distribution showed a bimodal pattern with an obvious decrease in abundance of large individuals. There was also a slight reduction in densities (73.2-60.1 ind./100 m2 at the sandy habitat), abundance (2292-1682 individuals) and biomass (21.6-11.3 kg/100 m2), and a marked shift towards deeper waters. Overfishing reached its maximum during the final 19 months of the study, and by October, 2003, density (30.7-0.4 ind./100 m2 at the sandy habitat), abundance (802-10 individuals) and biomass (6.9-0.1 kg/100 m2) were all greatly reduced. The size frequency distribution of the population became unimodal, large animals disappeared and no recruits were seen. During this period, individuals were found at very deep depths (30 to >40 m). The study also showed that sandy substrate was the preferred habitat for H. scabra, accommodating the largest number of individuals. The population of H. scabra at Abu Rhamada Island was found to spawn biannually from 1999 to 2001, then only once during 2002 when high fishing pressure occurred, and ceased completely in 2003. The sex ratio was not significantly different from 1:1 before fishing begun, but shifted to an increasing male bias reaching 93% males by January 2003. None of the small animals remaining after January, 2003 could be sexed. Size at sexual maturity decreased from prefishing (185 mm for females and 160 mm for males) to 155 mm for females and 125 mm for males in January 2003. There was a positive relationship between fecundity and size. And oocyte/female was highest in 1999 (0.73-1.7 million) and 2000 (0.75-1.72 million), decreased during 2001 (0.2-0.85 million) to reach its minimum at 2002 (0.28-0.29 million).

Isolation and Partial Characterization of a Lectin from the Internal Organs of the Sea Cucumber (Holothuria scabra Jaeger)

Isolation and Partial Characterization of a Lectin from the Internal Organs of the Sea Cucumber (Holothuria scabra Jaeger)

Preservation of genetic diversity in restocking of the sea cucumberHolothuria scabrainvestigated by allozyme electrophoresis

Population genetics analyses should be considered when releasing hatchery-produced juveniles of the sea cucumber Holothuria scabra when spawners from nonlocal populations are used. In New Caledonia, within-region genetic heterogeneity of H. scabra populations (examined through allozyme electrophoresis of 258 animals) indicated high gene flow between nine sites and FSTvalues did not deviate significantly from zero. However, exact tests indicated that populations at two sites with limited water exchange in the southern location were significantly different from populations at three other locations on the west coast. Inclusion of H. scabra sampled in Bali (n = 90) and Knocker Bay, Australia (n = 47), and comparisons with existing data from the west Pacific (Torres Strait, Solomon Islands, Upstart Bay, Hervey Bay) showed that populations were significantly different (using exact tests) and samples partitioned distinctly using unweighted pair group method with arithmetic mean clustering. Rogers' genetic distance values between populations were significantly related to geographic distances, showing a pattern of isolation by distance. The rapid increase in genetic distance over the first few hundred kilometres supports the view that the spatial extent of any translocation needs to be carefully considered on the basis of knowledge of variation in allele frequencies within the target area.

Antifouling activity of bioactive substances extracted from Holothuria scabra

Methanol extract of Holothuria scabrawas tested for antifouling activity using `mollusc foot adherence bioassay'. It was found that the secondary metabolites of H. scabraeffectively prevented foot adherence of P. vulgataat various concentrations. Based on the present findings it could be inferred that the bioassay guided purification and fractionation may give forth potent novel antifouling compounds.

The skin ulceration disease in cultivated juveniles of Holothuria scabra (Holothuroidea, Echinodermata)

It is frequently reported that cultivated holothuroids can suffer from a disease affecting their integument. We report here on a disease of juvenile Holothuria scabra, the widely marketed edible sea cucumber, reared in the Aqua-Lab hatchery of Toliara, Madagascar. This disease, which has been called skin ulceration disease, is very contagious and results from a severe bacterial infection that causes death within 3 days. The first sign of the infection is a white spot that appears on the integument of individuals, close to the cloacal aperture. The spot extends quickly onto the whole integument leading to the death of individuals. Microscopic (histology, scanning and transmission electron microscopies) and biomolecular (denaturing gradient gel electrophoresis (DGGE) and sequencing) techniques have been used to describe the lesions and to investigate the infecting microbial communities. The lesions consist in a zone where the epidermis is totally destroyed and where collagen fibres and ossicles are exposed to the external medium. This zone is surrounded by a border line where degrading epidermis is mixed with the connective tissue. Lesions include three bacterial morphotypes: rod-shaped bacteria, rough ovoid bacteria, and smooth ovoid bacteria. The last morphotype is the only one found on the ossicles and is assumed to be responsible for their degradation. Three species of bacteria have been put in evidence in the lesions thanks to biomolecular analyses: Vibrio sp., Bacteroides sp., and an α-Proteobacterium. Infection assays of healthy holothuroids have been performed from lesions and from bacterial cultures but the causative agent has not been identified. It is suggested that combined events or agents, including bacteria, are required to induce the disease.

Reproduction of the commercial sea cucumber Holothuria scabra (Echinodermata: Holothuroidea) in the Solomon Islands

Over a 3-year period (1996–1998), reproduction of the commercial sea cucumber Holothuria scabra (Jaeger, 1833) was investigated in the Solomon Islands to determine the spawning pattern and whether gametogenesis is continuous or seasonal. The gonad consisted of a single cohort of tubules that developed uniformly. Macroscopic examination of the gonads revealed that mature gametes were present throughout the year. Individuals with gonads at different stages of maturity were present in most samples. Partly spawned gonads were prevalent in females, whereas mature gonads were prevalent in males. The time at which the peak gonad index was recorded differed among years. Although gametogenesis was continuous, with a potential for prolonged gamete release, a period of enhanced spawning occurred during the dry season, from September to December. Maximum gonad indices were reached prior to and during this period of enhanced spawning. Histology revealed that gametogenesis reinitiated in partly spawned gonads, resulting in the presence of gametes at different stages of development in the gonad. The uniform growth of gonad tubules indicated that H. scabra does not conform to the progressive tubule recruitment model described for holothurian oogenesis. Continuous reproduction in H. scabra and prolonged availability of mature gametes would facilitate use of this species for aquaculture.

Development of three commercial sea cucumbers, Holothuria scabra, H. fuscogilva and Actinopyga mauritiana: larval structure and growth

Development of the tropical sea cucumbers Holothuria scabra, H. fuscogilva and Actinopyga mauritiana was investigated. Holothuria scabra developed through the feeding auricularia, the non-feeding doliolaria and the pentactula larval stages in 14–17 days at 26–28�C. Holothuria fuscogilva and A. mauritiana were reared to the auricularia and doliolaria stages respectively. The auricularia stage was reached by 40–70 h and the larvae developed lateral processes and a prominent ciliated band. Transformation to the doliolaria stage took 10–12 h and occurred on Days 9–12 in H. scabra and Days 12–22 in A. mauritiana. During this transition the ciliated band fragmented into ciliary rings, the location of which coincided with the lateral processes in the auriculariae. In H. scabra, metamorphosis to pentactulae (13–15 days) was marked by development of five primary tentacles and a ventroposterior podium. This podium was used to attach to the substratum. Newly settled pentactulae of H. scabra used their tentacles to test, adhere and move across the substratum. Development of a second podium marked the development of juveniles (14–17 days). Hyaline spheres were conspicuous in late auriculariae of H. scabra and may be an indicator of larval competence. They disappeared in the doliolaria stage, which suggests that they may function as nutritive reserves to sustain H. scabra through the non-feeding perimetamorphic period. Absence of these spheres in H. fuscogilva, and their poor growth in A. mauritiana, suggests the feeding protocol used may not be sufficient to support complete development in these species. Determination of food and culture conditions that promote hyaline sphere formation and control bacteria may be essential for successful culture of H. fuscogilva and A.�mauritiana.

Variation in short-term survival of cultured sandfish (Holothuria scabra) released in mangrove–seagrass and coral reef flat habitats in Solomon Islands

Juvenile cultured sandfish (Holothuria scabra) with a mean size of 35.6 mm±11.4 S.D. were released on soft substrata near mangrove–seagrass and lagoonal coral reef flat habitats in the Western Province of Solomon Islands. Mean survival of H. scabra at the mangrove–seagrass sites was 95–100% 1 h after release and approximated 70% 3 days later. At the coral reef flat sites, however, mean survival was as low as 37.5% 1 h after release and total mortality occurred in two of the three releases within 48 h. Mortality of the juvenile H. scabra was due mainly to predation by fish in the families Balistidae, Labridae, Lethrinidae and Nemipteridae. Survival of juvenile H. scabra was improved significantly by releasing them within a cage of 8-mm mesh. This procedure resulted in 100% survival of juveniles in the coral reef flat habitat during the course of the experiment. Our data indicate that mangrove–seagrass areas should be suitable habitats for release of cultured juvenile sandfish in restocking and stock enhancement programs. Release of sandfish at night, to coincide with the time they emerge during their inherent diel burrowing cycle, and the short-term use of protective cages, should be investigated to improve survival of individuals released in mangrove–seagrass habitats.

Spawning induction of three tropical sea cucumbers, Holothuria scabra, H. fuscogilva and Actinopyga mauritiana

Tropical sea cucumbers, Holothuria scabra, H. fuscogilva and Actinopyga mauritiana were collected from the wild, held in insulated containers and transported by a combination of sea, air and road transport for up to 12 h. Methods for obtaining reliable supplies of fertilised eggs from wild-caught broodstock were investigated. Of the 779 H. scabra collected, 4.5% eviscerated during transport, compared with 11.0% of the 181 H. fuscogilva and none of the 52 A. mauritiana. Experiments conducted in 20-l containers, with and without sea water and temperature control, determined that H. scabra survived for over 80 h, H. fuscogilva for 8 h and A. mauritiana for 20 h, in static seawater at 29 °C. Spawning of H. scabra in Solomon Islands can be induced throughout the year, but only in 3 months for H. fuscogilva (from August to October), and 2 months for A. mauritiana (from October to November). The peak spawning period for all three species was during the dry season: August–November. Collection, transport and thermal stress was an effective spawning induction method for H. scabra and A. mauritiana. Induced egg production in H. scabra was greatest in September, when 35% of broodstock spawned. Spawning appeared to be entrained to a lunar cycle in H. scabra, and occurred more readily during the afternoon and early evening. Addition of dried Schizochytrium sp. induced spawning in H. fuscogilva and was far more effective than thermal induction. Females of all three species were highly fecund and capable of multiple spawning. The mean number of fertilised eggs was: 1.9 million (±0.6 S.E., n=17) for H. scabra; 2.6 million (±0.2 S.E., n= 5) for H. fuscogilva and 2.6 million (±0.1 S.E., n=6) for A. mauritiana. The techniques for inducing spawning identified in this study allowed the collection of fertilised eggs for experimental and pilot-scale mass production of juvenile sea cucumbers. Further research should target improved spawning induction through the conditioning and holding of captive broodstock.

Restricted gene flow between Holothuria scabra (Echinodermata: Holothuroidea) populations along the north-east coast of Australia and the Solomon Islands

To describe patterns of gene flow for the fished holothurian species Holothuria scabra 17 to 141 individuals were collected from 8 populations from north-east Australia, the Torres Strait, and the Solomon Islands. Samples were investigated by allozyme electrophoresis of 7 polymorphic loci. Cluster analyses using Rogers' genetic distance identified 3 distinct groups of populations from the north-east coast of Australia, representing samples from the 3 regions Hervey Bay, Upstart Bay and Torres Strait. Populations in the latter region were closely connected to those from the Solomon Islands. F-statistics indicated restrictions in gene flow (average genetic variation between popula- tions, FST = 0.088). Hierarchical analyses revealed that 94.7% of the variation was within sampling locations. Approximately 77% of the variance among populations was due to differences between regions, and 23% within regions (most of the latter caused by differences between the 2 Solomon Island populations). Mantel's tests indicated that a high proportion of the variation in genetic dis- tances along the north-east coast of Australia was explained by isolation by distance (Mantel's nor- malised Z = 0.88). This proportion reduced when the Solomon Islands were included (Z = 0.65). The detection of separate stocks along the north-east coast of Australia is an important finding that has significant consequences for the development of sustainable management plans for this species. Low dispersal may significantly reduce recovery of overfished areas if no local refugia are provided.

Induction of Spawning in the Sea Cucumber Holothuria scabra (Echinodermata: Holothuroidea)

AbstractWith the advent of sea cucumber aquaculture in the South Pacific region, a reliable method is needed to induce large numbers of animals to spawn in captivity. Broodstock of the sea cucumber Holothuria scabra, collected from Stradbroke Island, Moreton Bay (27°90′N, 153°24′E) Australia, during the reproductive season from October to January, were used in spawning trials. During the 1997–1998 summer between one to five weeks of captivity, 100% of animals were induced to spawn in four trials at dusk on or close to a new or full moon, using nine males and nine females contained in a Reln tank and 30 cm of filtered sea water, using a 3–5 C temperature shock. H. scabra was induced to spawn in small numbers during the 1996–1997 summer despite a marked degree of weight loss, and all animals spawned during 1997–1998 with minimal loss of weight. The difference in the number of spawned eggs between animals of similar size and mean numbers of spawned eggs in consecutive trials decreased the longer animals were held in captivity before spawning. The hatch rate of eggs was reduced significantly for broodstock held for more than one month. Hatch rate and numbers of spawned eggs are important indicators of egg viability of broodstock maintained in captivity for an extended period.

Settlement preferences and early migration of the tropical sea cucumber Holothuria scabra.

Settlement and post-settlement processes of the sea cucumber Holothuria scabra Jaeger were studied in the laboratory. Independent and paired choice experiments revealed that several substrates could induce metamorphosis into pentactulae, but that specific substrates favoured settlement. Leaves of seagrass Thalassia hemprichii, with or without their natural bio-film, yielded the highest settlement rates (4.8-10.5%). T. hemprichii was preferred as a settlement substrate over sand, crushed coral, several other plant species and artificial seagrass leaves with or without a bio-film. Only settlement on the seagrass, Enhalus acoroides, was similar to that recorded for T. hemprichii. In the absence of a substrate, the larvae delayed settlement for nearly 96 h and survival was less than 0.5%. Sand and crushed coral, either alone or together, induced settlement from <1.5% of the available larvae. The pentactulae found on sand, coral and in bare containers were 10-35% smaller than those on T. hemprichii leaves. Soluble extracts from T. hemprichii and E. acoroides successfully induced metamorphosis and settlement on clean plastic surfaces. Newly settled juveniles remained on the seagrass leaves for 4-5 weeks before migrating to sand at around 6 mm in length. Prior to this, the juveniles spent 4-5 days moving on and off the leaves. Once on the sand, the juveniles became deposit-feeders, but did not show the typical burrowing behaviour of older specimens until they reached around 11 mm in length. The larvae of H. scabra appear to actively select seagrass leaves, possibly through chemical detection. We hypothesise that larvae settling on seagrass have an increased chance of growth and survival because they are provided with a suitable substrate on which to grow, and a bridge to sand substrates as they become deposit-feeders.

Ossicle change in Holothuria scabra with a discussion of ossicle evolution within the Holothuriidae (Echinodermata)

Ossicles of Holothuria (Metriatyla) scabra Jaeger 1833 vary mainly in early juveniles between 0.9 and 15mm long. While ossicles were not observed in auricularia and doliolaria larvae, which instead possessed elastic balls, ossicles were present in late pentactulae. Specimens 0.9–1.5mm long have tables with tall spire (4–5 cross beams), no buttons, and large irregular perforated plates. Specimens 5–6mm long have tables with moderate spire (2–4 cross beams) and a few smooth buttons. Specimens 9–16mm long have tables with low spire (1–2 cross beams) and knobbed buttons. From 30mm, ossicle are similar to those of adults, with more buttons and fewer tables. Several features of the ossicles of early juveniles, including their size, shape and prevalence, are unique to the species. Comparison with holothurian juveniles of other species indicates that presence of tables with tall spire and absence of buttons are plesiomorph characters in the evolution of the Holothuriidae.

Life cycle of the pea crabpinnotheres halingisp. Nov., an obligate symbiont of the sea cucumberholothuria scabrajaeger

Abstract A new species of pea crab, Pinnotheres halingi sp. nov. (Pinnotheridae), found encysted in the right respiratory tree of the sea cucumber, Holothuria scabra (Holothuridea), from Solomon Islands, is described. The reproduction, infestation and pairing behaviour of the crabs were investigated through field observations and experiments. Infestation frequency in 8 monthly samplings of 25–30 holothurians was 98.6±2.6% in Kogu Halingi bay and 0% in two nearby sites. Of 403 pea crabs, 91.4% were found in pairs of opposite sex, 7.9% were single females and <1% were single males. The embryos developed on the female pleopods over ca. 30 days from fertilisation to the release of first zoeae and subsequently went through five pelagic zoeal stages. Infestation occurred at the megalops stage after about 59 days of development. A single pea crab (male or female) per host was found three months after larval infestation. Young males appeared to be strongly attracted to hosts that sheltered a single female, suggesting that pairing occurred as a male <6 mm carapace width joined a female. Larger crabs could not enter the host. Copulation was observed within the female cyst, preceding or overlapping oviposition. The male then progressed away from the female and from the anus, forming its own cyst along the way. Both larvae and small sub-adults invaded H. scabra with a minimum length of 80 mm, exclusively. P. halingi induced atrophy of the right respiratory tree of its host.

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.