Tropical Sea Cucumber Research Articles

Isolation and characterization of 21 microsatellite loci for the sea cucumber Holothuria (Halodeima) atra (Echinodermata, Holothuroidea) reveal low asexual propagation through time in Reunion Island (southwestern Indian Ocean).

Holothuria (Halodeima) atra Jaeger, 1833 is a tropical sea cucumber usually harvested for the "bêche-de-mer" trade market. It has been reported to reproduce both sexually, through gamete spawning, or asexually, through fission. To date, no study has ever investigated clonality, nor genetic connectivity, among its populations, using microsatellite markers. We isolated the first 21 microsatellite loci specific for H.atra, which were then used to investigate clonal diversity, genetic structure and diversity among 44 H.atra individuals sampled in Reunion Island (southwestern Indian Ocean), over two seasons. All 21 loci were polymorphic, with number of alleles per locus ranging from 2 to 10. No repetitive multi-locus genotype (MLG) and few clonal lineages (MLL) were found. Observed heterozygosities per locus and season ranged from 0.000 to 0.909, while expected heterozygosities ranged from 0.290 to 0.882. Four loci were at Hardy-Weinberg equilibrium for both seasons, all others presenting a deficit of heterozygotes in one or both seasons. Meanwhile, no genetic differentiation was detected between seasons, according to assignment tests and global FST. These results suggest low asexual propagation in this population. These loci represent useful tools to better understand reproductive strategies and population connectivity of H.atra, and thus provide relevant knowledge for efficient management.

Evolving governance structures in community-based sandfish mariculture and their interactions with livelihood outcomes: Evidence from the Philippines

Sea cucumber mariculture is an important emerging field of practice and applied research in the coastal tropics. This is due to the existing importance of tropical sea cucumber fisheries for wealth generation and poverty reduction, and the potential for mariculture to contribute to the longer term sustainability of these fisheries while generating benefits additional to those from wild caught sea cucumber. Understanding the optimal institutional arrangements for sea cucumber mariculture is an important area of focus in this field, with a variety of arrangements currently in place. This paper documents the establishment of a communal form of sea ranching in the Philippines, as a case study of community level institutional processes. It describes the background to establishment of the sea ranch in the community of Victory, challenges encountered and how these were managed, and the evolution of governance arrangements. In charting this process, we assess the impacts on livelihood outcomes, highlighting this as a crucial aspect influencing this evolution and the nature of community involvement in the sea ranch. While the sea ranching project generated a range of benefits for livelihoods, including possible spillover effects for the surrounding fishery, substantial economic returns from harvests did not occur. Thus, the system of governing the sea ranch evolved from a communal model to a more exclusive household model primarily to improve operational efficiency. In order for possible benefits of the sea ranch to be sustained and enhanced, greater integration with fisheries management and government support will be needed.

Effects of Diet on Larval Survival, Growth, and Development of the Sea Cucumber Holothuria leucospilota.

Because most tropical sea cucumbers have been overexploited around the world, the sea cucumber Holothuria leucospilota has become increasingly commercially important in recent years. Restocking and aquaculture of H. leucospilota using hatchery-produced seeds could both enhance declining wild populations and provide sufficient beche-de-mer product to satisfy increasing market demand. Identifying an appropriate diet is important for successful hatchery culture of the H. leucospilota. In this study, we trialed different ratios of microalgae Chaetoceros muelleri (2.00-2.50 × 106 cells/mL) and yeast (Saccharomyces cerevisiae, ~2.00 × 106 cells/mL) in diets for H. leucospilota larvae (6 d after fertilization, referred to as "day 0") at proportions 4 : 0, 3 : 1, 2 : 2, 1 : 3, and 0 : 4 by volume, in 5 treatments (A, B, C, D, and E, respectively). Larval survival rates in these treatments decreased over time, with the survival highest in treatment B (59.24 ± 2.49%) on day 15 (double that of the lowest rate in treatment E (28.47 ± 4.23%)). For any sampling event, larval body length in treatment A was always the lowest after day 3, and that for treatment B was always the highest, except on day 15. The maximum percentage of doliolaria larvae occurred in treatment B (23.33%) on day 15, followed by treatments C, D, and E (20.00%, 10.00%, and 6.67%, respectively). No doliolaria larvae occurred in treatment A, and pentactula larvae occurred only in treatment B (3.33%). On day 15 in all treatments, late auricularia larvae had hyaline spheres, but these were not prominent in treatment A. Densities of juveniles attaching to settlement plates varied with treatments, and the values were very low for the larvae only fed microalgae (A, 2.39 ± 1.95 ind per plate) or yeast (E, 2.13 ± 1.05 ind per plate)-only ~5% of the maximum number settling in treatment B (45.56 ± 7.24 ind per plate). Increased larval growth, survival and development, and juvenile attachment indicates that diets combining microalgae and yeast are more nutritionally balanced than single diets for hatchery of H. leucospilota. A combined diet of C. muelleri and S. cerevisiae at a 3 : 1 ratio is optimum for the larvae. Based on our results, we propose a larval rearing protocol to facilitate mass production of H. leucospilota.

Deaminative-cleaved S. monotuberculatus fucosylated glycosaminoglycan: Structural elucidation and anticoagulant activity

Stichopus monotuberculatus is a tropical sea cucumber species and used as a folk medicine and tonic food. In this study, a fucosylated glycosaminoglycan (SmFG), the depolymerized SmFG (dSmFG) and its oligosaccharide fractions were prepared. The SmFG and its depolymerized products were comprised of a chondroitin-sulfate-E backbone, and various sulfated fucose side chains, including an unusual disaccharide side chain connected to the C-3 position of D-glucuronic acid (GlcA) or GlcA-ol. A peeling reaction occurred during the deaminative depolymerization process. The dSmFG and its fractions showed strong anticoagulant activity by selectively inhibiting intrinsic tenase complex, and had no anti-factor IIa, Xa and VIIa activity. The anticoagulant activity reduced with the decrease of molecular weight, and the unusual branch and novel reducing end may enhance the anticoagulant activity. These findings can provide significant information for development and utilization of depolymerized products from SmFG in food and pharmaceutical industries.

Comparative Analysis of In Situ Eukaryotic Food Sources in Three Tropical Sea Cucumber Species by Metabarcoding.

Simple SummaryThere are large numbers of sea cucumbers naturally inhabiting tropical seas, which play an important ecological role in the habitat through their biological activity. However, despite the diversity of tropical sea cucumbers, until now there have been few studies on their exact eukaryotic food sources. In the present study, we systemically investigated the eukaryotic food sources of three sea cucumber species. We also study the differences of eukaryotic composition among three sea cucumber species and provide new insight into reasons for the differences. The reported information could be valuable in further biological and ecological studies of these species.In this study, the eukaryotic composition of gut contents in three tropical sea cucumber species, Stichopus monotuberculatus, S. chloronotus and Holothuria atra were surveyed and compared by metabarcoding analysis based on 18S rRNA gene V4 region. The sequences were assigned to 21.80 ± 1.07, 22.60 ± 0.68 and 22.40 ± 0.25 different phyla from the gut contents of S. monotuberculatus, S. chloronotus and H. atra, respectively, and those in sediment samples were assigned to 21.00 ± 1.67 phyla. The results of α-diversity showed that surface sediments had a greater eukaryotic diversity than gut contents, yet the guts of sea cucumbers had an enrichment effect on some microorganisms, including Diatomea and Apicomplex. A comparison of the gut eukaryotic community among the three species suggested that the feeding preference was different: S. monotuberculatus fed mainly on Diatomea and Arthropoda, and the other two species had higher Apicomplexa concentrations, which may be due to differences in the morphology of the tentacles and habitat preferences. Moreover, obvious different eukaryotic community composition in the gut contents of the three sea cucumber species and the surrounding sediments also might result from the animals’ selective feeding for sediment patches. The current study filled in gaps about feeding mechanisms of tropical sea cucumbers and provided a basis for further exploring the mechanism about selective feeding and sea cucumber–sediment interaction in the future.

Nondestructive and rapid method for sex identification of the tropical sea cucumber Holothuria scabra by anal swab sampling

As one of the most economically significant sea cucumber species, Holothuria scabra are naturally distributed in the Indo-West Pacific region and are widely cultural in Southeast Asia. The appearances of female and male H. scabra have no obvious phenotypic dimorphism. Thus, identification of sex-specific markers and establishment of sex detection methods are beneficial to artificially induced reproduction and genetic breeding in this species. In this study, a total of 26 male-specific and 9 female-specific sequences were obtained by genomic sequencing with 3 male and 3 female independent samples and a female mixed pool with 10 individuals of H. scabra. After PCR confirmation, two primer pairs (HSM24 and HSM25) for male-specific sequences were found to be true positive for all male individuals. Based on a male-specific marker (GenBank: OP218794), primers were designed for PCR, and loop-mediated isothermal amplification (LAMP) methods were further tested on another 30 sex-unknown individuals with DNA samples collected from a nondestructive anal swab method. In this case, the accuracies for PCR and LAMP were approximately 100%. Altogether, this study provided a nondestructive and rapid method for sex identification of H. scabra, which may contribute to the aquaculture of this economic species.

Sea Ranching Feasibility of the Hatchery-Reared Tropical Sea Cucumber Stichopus monotuberculatus in an Inshore Coral Reef Island Area in South China Sea (Sanya, China)

Sea ranching of tropical edible sea cucumbers is an effective way to relieve the overfishing stress on their natural resources and protect the coral reef ecosystem, yet only a few species have been applied in the sea ranching practice based on hatchery-reared juveniles around the world. In this study, an 8-month (April to December) sea ranching study for hatchery-reared edible sea cucumber Stichopus monotuberculatus juveniles was carried out at a tropical coral reef island area in Sanya, China. Several growth performance indexes and basal nutritional components were monitored. Results revealed that the sea cucumbers had a growth rate of 0.35~0.78 mm day-1 during the experimental period, reaching 15.9 cm long before winter. The weight gain reached 491.13% at the end, and most sea cucumbers were able to grow to the commercial size (over 150 g WW) in the first year of sea ranching. The overall specific growth rate (SGR) and survival rates were 0.73 and 27.5%. Most of the death occurred in the first month after release (25.0%–37.5%), and this is probably due to inadaptation to the sudden change of the environment from the hatchery to the wild, which is proved by the remarkable decrease in nutritional indexes (amino acids, total lipid, and crude protein). Stable isotope and lipid biomarkers revealed that the food source mainly comes from water deposits (with microbes), Sargassum sanyaense seaweed debris, phytoplankton, and coral mucus-derived organics. The study proved the feasibility of the sea ranching of the hatchery-reared S. monotuberculatus juveniles in the tropical coral reef island area. Also, it is highly recommended that appropriate acclimation operation before release should be carried out to improve the survival rate of this species.

Influence of Water Temperature and Flow Velocity on Locomotion Behavior in Tropical Commercially Important Sea Cucumber Stichopus monotuberculatus

Sea cucumber Stichopus monotuberculatus is one species of tropical sea cucumbers with high recognition and economic value. While advances have been made in the nursery rearing of the sea cucumber, influence of environmental factors on its locomotion behavior remains less understood, which restricts the establishment of mariculture technologies. In the present study, locomotion behavior of S. monotuberculatus under different temperatures and flow velocities were examined through controlled simulation experiments. Results showed that the creeping activities were obviously affected by temperature, and the most active movement and feeding behavior were recorded at relatively high temperatures. Diurnal variation of locomotion and feeding activities indicated that S. monotuberculatus displayed an evident nocturnal activity pattern, being the most active at night, exhibiting intermediate activity at dusk, and minimal activity during the daytime. The movement velocity decreased with the increasing flow speed and was only 1.65 ± 1.35cm·min-1 in the highest flow rate group (20.8 ± 3.4cm/s). Moreover, the sea cucumber S. monotuberculatus displayed positive rheotaxis behavior of moving downstream at all flow velocities. Overall, the sea cucumber S. monotuberculatus exhibited high locomotor and feeding activities at night of relatively high temperature, and its favoured flow regime was downstream and low water velocity area. These findings may assist the sea ranching and aquaculture development of the tropical commercial sea cucumber species.

Apoptosis-Inducing Factor 2 (AIF-2) Mediates a Caspase-Independent Apoptotic Pathway in the Tropical Sea Cucumber (Holothuria leucospilota).

Apoptosis, also known as programmed cell death, is a biological process that is critical for embryonic development, organic differentiation, and tissue homeostasis of organisms. As an essential mitochondrial flavoprotein, the apoptosis-inducing factor (AIF) can directly mediate the caspase-independent mitochondrial apoptotic pathway. In this study, we identified and characterized a novel AIF-2 (HlAIF-2) from the tropical sea cucumber Holothuria leucospilota. HlAIF-2 contains a conserved Pyr_redox_2 domain and a putative C-terminal nuclear localization sequence (NLS) but lacks an N-terminal mitochondrial localization sequence (MLS). In addition, both NADH- and FAD-binding domains for oxidoreductase function are conserved in HlAIF-2. HlAIF-2 mRNA was ubiquitously detected in all tissues and increased significantly during larval development. The transcript expression of HlAIF-2 was significantly upregulated after treatment with CdCl2, but not the pathogen-associated molecular patterns (PAMPs) in primary coelomocytes. In HEK293T cells, HlAIF-2 protein was located in the cytoplasm and nucleus, and tended to transfer into the nucleus by CdCl2 incubation. Moreover, there was an overexpression of HlAIF-2-induced apoptosis in HEK293T cells. As a whole, this study provides the first evidence for heavy metal-induced apoptosis mediated by AIF-2 in sea cucumbers, and it may contribute to increasing the basic knowledge of the caspase-independent apoptotic pathway in ancient echinoderm species.

First trial of wild juvenile collection of tropical sea cucumbers from settling larvae, using coconut fibre from waste husks in Solomon Islands: A new conservation tool

Abstract Wild juvenile collection (WJC) from settling larvae has been reported for two temperate holothurians (Apostichopus japonicus and Apostichopus californicus), mainly for the objective of restocking, but its applicability to tropical holothurians is unknown. This study, for the first time, tested the applicability of WJC for tropical sea cucumbers. First, hatchery‐produced larvae of peanutfish (Stichopus horrens) before settlement were introduced in a tank in which bundles of coconut fibre, rolled mesh bags, and oyster shells were suspended to identify the most suitable settlement material. The results showed that the coconut fibre and mesh bags collected more settling larvae than the oyster shells. Second, 25 collectors were installed for 3 months in the field in Nggela, Solomon Islands. The newly designed simple collector comprised between two and four net bags filled with coconut fibre, which were tied to a rope vertically moored between a concrete block anchor and polyethylene terephthalate (PET) bottle floats. A total of 14 juvenile holothurians were collected, including Stichopus cf. horrens, stonefish (Actinopyga lecanora), kingfish (Synapta maculata), and five unidentified species. It is characteristic of tropical WJC that diverse species can be collected simultaneously (including rare, non‐culturable species), which is advantageous over hatchery production for restocking purposes. The total yield corresponded to approximately 1% of the total abundance of the ambient holothurian community, demonstrating potential for restocking, considering the ease of the extension and repetition of the trials. Collection in the inner bay areas was successful, whereas rough weather physically damaged the collectors in areas open to the ocean. These results show that WJC is a viable option for tropical holothurians. Thus, the use of the low‐cost, simple collectors using coconut fibre could be a new conservation measure for endangered holothurian resources, and are manageable by local communities.

Cancer Cell Inhibiting Sea Cucumber (Holothuria leucospilota) Protein as a Novel Anti-Cancer Drug.

Cancer remains the primary cause of death worldwide. To develop less toxic anti-cancer drugs to relieve the suffering and improve the survival of cancer patients is the major focus in the anti-cancer field. To this end, marine creatures are being extensively studied for their anti-cancer effects, since extracts from at least 10% of the marine organisms have been shown to possess anti-tumor activities. As a classic Chinese traditional medicine, sea cucumbers and compounds extracted from the sea cucumbers, such as polysaccharides and saponins, have recently been shown to exhibit anti-cancer, anti-inflammatory, and anti-oxidant effects. Holothuria leucospilota (H. leucospilota) is a tropical edible sea cucumber species that has been successfully cultivated and farmed in large scales, providing a readily available source of raw materials to support the development of novel marine anti-cancer drugs. However, very few studies have so far been performed on the biological activities of H. leucospilota. In this study, we first investigated the anti-cancer effect of H. leucospilota protein on three cancer cell lines (i.e., HepG2, A549, Panc02) and three normal cell lines (NIH-3T3, HaCaT, 16HBE). Our data showed that H. leucospilota protein decreased the cell viabilities of HepG2, A549, HaCaT, 16HBE in a concentration-dependent manner, while Panc02 and NIH-3T3 in a time- and concentration-dependent manner. We also found that the inhibitory effect of H. leucospilota protein (≥10 μg/mL) on cell viability is near or even superior to EPI, a clinical chemotherapeutic agent. In addition, our data also demonstrated that H. leucospilota protein significantly affected the cell cycle and induced apoptosis in the three cancer cell lines investigated; in comparison, it showed no effects on the normal cell lines (i.e., NIH-3T3, HaCaT and 16HBE). Finally, our results also showed that H. leucospilota protein exhibited the excellent performance in inhibiting cell immigrations. In conclusion, H. leucospilota protein targeted the cancer cell cycles and induced cancer cell apoptosis; its superiority to inhibit cancer cell migration compared with EPI, shows the potential as a promising anti-cancer drug.

Assessing the Viability of Commercial Media for the Mass Culture of Chaetoceros muelleri

The microalgae Chaetoceros muelleri is considered a highly nutritious feed for the cultured larvae of the tropical sea cucumber Holothuria scabra. Due to the cost of analytical grade culture media used in the production of C. muelleri, there is a need to evaluate cheap alternative commercial media to decrease the cost of producing quality live microalgal food. In this study, two different indoor batch culture systems (1 L glass bottles and 10 L plastic carboys) were used to evaluate the effectiveness of two conventional (modified F/2 and Walne’s) and one commercial (Epizyme AGP complete) microalgal culture media. Results of the 1 L glass bottle experiment showed that the peak cell density of C. muelleri in AGP (1,241 ± 116 x 104 cells ml-1) was not significantly different from the modified F/2 (1,584 ± 41 x 104 cells ml-1) and Walne’s medium (1,319 ± 162 x 104 cells ml-1) (Kruskal-Wallis test, p=0.78). Likewise, in the plastic carboy experiment, the maximum cell density of C. muelleri in Walne’s medium (750 ± 144 x 104 cells ml-1) and F/2 medium (653 ± 79 x 104 cells ml-1) were higher, but not significantly different from AGP (496 ± 184 x 104 cells ml-1) (Kruskal-Wallis test, p=0.43). The highest growth rate in the glass bottle cultures was the modified F/2 (0.38 div day-1), while AGP was the lowest (0.34 div. day-1). On the other hand, in carboy culture, AGP was higher (0.17 div.day-1) compared to modified F/2 (0.15 div. day-1) and Walne’s medium (0.13 div. day-1). The exponential growth phase was similar in the glass bottles, while in the carboy, the exponential phase was reached at a shorter time in the AGP treatment than those in the modified F/2 and Walne’s media. The findings showed that AGP medium is an adequate alternative to replace the conventional media (modified F/2 and Walne’s) during the secondary stock culture for C. muelleri. The viability of using cheaper and more readily available commercial AGP media for the indoor culture production of C. muelleri can contribute to cost-effective scaling-up of the hatchery production of quality H. scabra larvae and early juveniles.

A Review of Factors Influencing the Seagrass-Sea Cucumber Association in Tropical Seagrass Meadows

In the tropical ecosystem, sea cucumbers are associated with seagrass meadows in various ways, often forming a network of ecological interactions. From this myriad of interactions, the trophic relationship between the seagrasses and sea cucumbers has received recent attention with the advent of analytical techniques. However, little is understood about the exact mechanism by which seagrasses are sustaining the sea cucumber populations in the food chain, considering the high number of refractory components in seagrasses and the lack of digestive enzymes among sea cucumbers. This manuscript aims to review existing concepts in ecology concerning the association between tropical seagrasses and sea cucumbers to provide directions for research and management of this vital resource. We searched literature from electronic databases and identified key concepts concerning sea cucumber and seagrass communities based on geographic distribution, nutrient compositions, seagrass decomposition process, and trophic enrichments in the food chain. A conceptual model was then developed detailing the factors influencing the association between the seagrass meadows and sea cucumbers. Despite the limited published information on the seagrass–sea cucumber association, a synthesis of the current understanding of this topic is provided to address the declining sea cucumber populations in the tropical seagrass meadows. We suggest that the successful restoration of sea cucumber fisheries requires a thorough understanding of the seagrass decomposition process, which is vital to the diet of sea cucumbers.

Performance of a trial sea ranch for the commercial sea cucumber, Holothuria scabra, in Papua New Guinea

Holothuria scabra (sandfish) is a tropical sea cucumber that has been over-exploited because of its high-value in the bêche-de-mer trade. It is amenable to mariculture and the potential for community-based sea ranching has been investigated in the Tigak Islands of Papua New Guinea (PNG). A 5-ha trial sea ranch was established within the fishing grounds of an island community and protected from fishing for the duration of this study. Over 10 months, 5655 fluorochrome-marked H. scabra juveniles were stocked into the centre of the sea ranch. Line-transects were used to survey sea cucumber within and on the periphery of the sea ranch prior to stocking the sea ranch (October 2018) and at the conclusion of the study (February 2020). Additional collections of H. scabra were made at night in a 1-ha area around the stocking site. All H. scabra were weighed and checked for fluorochrome marks to determine cultured or wild origin. An estimated 3.7 ± 0.9% of cultured H. scabra were recoverable in the post-stocking survey. Cultured juveniles were found at a significantly higher density only around the stocking site. Factors potentially contributing to low recovery of cultured H. scabra include mortality, being overlooked, migration and misidentification of cultured and wild individuals. Species richness and density of the wild sea cucumber community increased in response to stocking and protecting the sea ranch. Our results highlight the importance of site-specific monitoring and evaluation to assess the success of sea ranching. Despite low recovery, H. scabra mariculture remains a promising option in PNG, as wild stocks are predicted to decline with increased fishing pressure, thus limiting recruitment. This will be aided by improved production of release-size juvenile H. scabra, improved release protocols to promote higher recovery of cultured juveniles and improved community capacity to manage cultured and wild sea cucumber stocks.

Bacterial community composition in gut content and ambient sediment of two tropical wild sea cucumbers (Holothuria atra and H. leucospilota)

Bacterial community composition in gut content and ambient sediment of two tropical wild sea cucumbers (Holothuria atra and H. leucospilota)

The Effects of Hypoxia and Anthropogenic Disturbance on the Distribution, Abundance and Recruitment of the Sea Cucumber Holothuria leucospilota at the Mouth of a Subtropical Bay, China

Despite the commercial importance of the sea cucumberHolothuria leucospilotaincreasing in recent years, little is known of its spatial distribution and ecology in the South China Sea. We investigate the distribution, abundance, and recruitment ofH. leucospilotafrom 2017 to 2020 at two sites (S1 and S2) in Daya Bay, a typical subtropical bay which is strongly influenced by human activities in the South China Sea. We report hypoxia to driveH. leucospilotafrom deeper into shallower waters with higher DO concentrations at the mouth of Dapeng Cove in Daya Bay (S1), particularly during summer. Population size at S1 decreased by 90% from 2017 levels, before this area was opened to the public in 2018; recruitment was not observed by August (summer) of 2020. In contrast, in summers of 2017 and 2020,H. leucospilotaabundance at S2, a protected open-water area, increased by 84%, and the proportion of small-sized (recently recruited) sea cucumber in the population increased by 20%. Severe summer hypoxia at S1 could negatively influenceH. leucospilotaspawning and larval settlement, which combined with depletion of broodstock because of fishing pressure and/or hypoxia-induced mortality, could inhibit recruitment. In contrast, higher DO concentrations and abundant broodstock during summer (the breeding season) favoured recruitment ofH. leucospilotaat S2. Overall, hypoxia and anthropogenic disturbance impede recovery ofH. leucospilotaat S1, while at the protected S2, larvae may be released to settle in nearby areas. It is imperative to develop a better understanding of the biology, ecology and conservation of tropical sea cucumbers in China.

Identification of sex-specific molecular markers and development of PCR-based sex detection techniques in tropical sea cucumber (Stichopus monotuberculatus)

Sex-specific markers are essential for understanding sex determination mechanism and developing sex detection techniques in aquatic animals. The tropical sea cucumber Stichopus monotuberculatus is a fledgling aquaculture species in southern China. In this study, a total of 399 candidate male-specific and 179 candidate female-specific sequences were obtained after genome assembly, read mapping, and sequencing depth and coverage analyses of the sequenced genomes from three males and three females. Based on the k-mer distribution and sex-specific sequence length distribution, S. monotuberculatus is speculated to belong to a male heterogametic sex determination system. Next, 10 female-specific and 10 male-specific sequences were chosen for a first round verification to identify the true sex-specific markers, and only the male-specific markers could be repeated by PCR examination. The primer pairs for male-specific sequences were subjected to a second round verification, and five of them distinguished the genetic sex of S. monotuberculatus with accuracies of near 100%. Based on one of the male-specific markers (SM-M3), we constructed a rapid and nonharmful PCR-based method for sex identification that was suitable in different geographical populations, and it was successfully applied to distinguish female and male S. monotuberculatus before they were used for artificial spawning. Overall, this study provided evidence of the male heterogametic sex determination system and established an effective way to identify sex in sea cucumbers, and these results may contribute to the aquaculture of these economic species.

Transcriptome analysis of growth variation in early juvenile stage sandfish Holothuria scabra

The sandfish Holothuria scabra is a high-value tropical sea cucumber species representing a major mariculture prospect across the Indo-Pacific. Advancements in culture technology, rearing, and processing present options for augmenting capture production, stock restoration, and sustainable livelihood activities from hatchery-produced sandfish. Further improvements in mariculture production may be gained from the application of genomic technologies to improve performance traits such as growth. In this study, we performed de novo transcriptome assembly and characterization of fast- and slow-growing juvenile H. scabra from three Philippine populations. Analyses revealed 66 unigenes that were consistently differentially regulated in fast-growing sandfish and found to be associated with immune response and metabolism. Further, we identified microsatellite and single nucleotide polymorphism markers potentially associated with fast growth. These findings provide insight on potential genomic determinants underlying growth regulation in early juvenile sandfish which will be useful for further functional studies.

Growth, Survival, and Behavior of Early Juvenile Sandfish Holothuria scabra (Jaeger, 1883) in Response to Feed Types and Salinity Levels under Laboratory Conditions

Aquaculture of the tropical sea cucumber Holothuria scabra or sandfish is still at a developing stage, especially in the Philippines. In Mindanao, early juveniles of sandfish were successfully produced at the Mindanao State University at Naawan (MSUN) sandfish hatchery for 5 yr now. However, on-site growing of these early juveniles in ocean nurseries often suffered very low survival rates. Two separate laboratory experiments were conducted for 60 d to test for the effects of feed types (Navicula sp., powdered Sargassum, and Sargassum extract) and salinity levels [ambient seawater at 32–35 (as control), 20, 25, and 40 ppt] on the growth, survival, and behavior of 7-wk-old early juvenile sandfish (2–15 mm in length). Juveniles fed with Sargassum extract significantly produced the highest increase in width and length, followed by powdered Sargassum and Navicula sp. with a survival rate of at least 71%. The highest growth rate (GR) and survival were observed with ambient salinity, followed by 40, 25, and 20 ppt. Unusual pale coloration, sluggish movement, and destroyed integument in some parts of the body were observed in some juveniles exposed to lower salinity indication of an unhealthy individual. Overall, Sargassum extract is an ideal feed for sea cucumber juveniles. Low salinity is stressful to early juvenile sandfish and that growth and behavior were adversely affected.

Single and mixed species of microalgae as larval food for the tropical sea cucumber Holothuria scabra

Single and mixed species of microalgae as larval food for the tropical sea cucumber Holothuria scabra