Juvenile Sandfish Research Articles

Differences in gut microbial diversity and composition between growth phenotypes of farmed juvenile sandfish, Holothuria scabra

BackgroundThe observed growth variability of different aquaculture species in captivity hinders its large-scale production. For the sandfish Holothuria scabra, a tropical sea cucumber species, there is a scarcity of information on its intestinal microbiota in relation to host growth, which could provide insights into the processes that affect growth and identify microorganisms with probiotic or biochemical potential that could improve current production strategies. To address this gap, this study used 16 S rRNA amplicon sequencing to characterize differences in gut and fecal microbiota among large and small juveniles reared in floating ocean nurseries.ResultsWe recovered 5915 amplicon sequence variants and diversity indices revealed significant differences between large and small juveniles (p < 0.05). Gut microbiota of large juveniles had lower bacterial diversity than its smaller counterparts. The genus cluster Burkholderia-Caballeronia-Paraburkholderia (BCP) is the most common and abundant taxa found in the gut for both size categories but less abundant in fecal samples. Small juveniles had a higher abundance of members from the Roseobacter clade (Rhodobacteriaceae) such as Ruegeria, Shimia, Psuedoruegeria and Marivita among others while the genus Schlegelella (Caldimonas) and Bosea were primarily found in larger juveniles. Predicted physiological functions identified signatures of metabolism, biosynthesis, and biodegradation pathways unique for each size category. Significant differences in diversity and composition were also exhibited between the pooled fecal and gut sample types.ConclusionsThe bacterial composition in the intestinal tract of the sandfish H. scabra is an important factor in the observed growth variability in aquaculture. The results show differences in diversity, composition and predicted physiological functions between the size groups, despite being from the same cohort and environment. It was also evident that the fecal microbiota differs from the gut and does not correspond to size category, warranting caution in using the fecal matter as a proxy to infer microbial composition and interactions in the gastrointestinal tract. Understanding the roles that these microorganisms play in sandfish growth could support the development of strategies to manage size variation in captive-bred sea cucumbers, or for the promotion and selection for faster-growing individuals.

The Nursery of Juvenile Sandfish, Holothuri scabra in Pen-culture

This research aims to be a reference for better and regionally characteristic sandfish nursery activities to support sustainable sea cucumber farming. This research was carried out in the waters of Ohoitel village, Tual City, and took place from March – April 2023. 450 sandfish seeds measuring 0.39 – 1.98 gr were stocked in Pen-culture measuring 4 x 3 x 0.7 meters. Pen culture is made of waring and has a cover. Calculation of survival and growth measurements only at the beginning and end of rearing. Water quality measurements (temperature, salinity, and pH) were carried out every week during the research. Based on the research results, it can be concluded that the nursery of seeds sandfish measuring 0.39 – 1.98 gr can be done in Pen-culture using a cover. This is because the survival percentage of sandfish chicks raised in Pen-culture is 84 - 86.67% with an average survival percentage of 85.33% and a body weight growth range of 2.54 - 12.97 gr with an average of the average absolute growth in body weight was 6.77 gr. Keywords: Nursery, Sandfish, Pen-culture Abstrak Penelitian ini bertujuan menjadi referensi kegiatan pendederan teripang pasir yang lebih baik dan berkarakteristik daerah guna menopang budidaya teripang secara berkelanjutan. Penelitian ini dilaksanakan di perairan desa Ohoitel, Kota Tual dan berlangsung dari Maret 2023 – April 2023. Benih teripang pasir berukuran 0,39 – 1,98 gr sebanyak 450 ekor ditebar pada Pen-culture berukuran 4 x 3 x 0,7 meter. Pen-culture terbuat dari waring dan memiliki penutup. Perhitungan kelangsungan hidup dan pengukuran pertumbuhan hanya pada awal dan akhir pemeliharaan. Pengukuran kualitas air (suhu, salinitas dan pH) dilakukan setiap minggu selama penelitian. Berdasarkan hasil penelitian dapat disimpulkan bahwa pendederan anakan teripang pasir berukuran 0,39 – 1,98 gr dapat dilakukan pada Pen-culture dengan menggunakan penutup. Hal ini dikarenakan presentase kelangsungan hidup anakan teripang pasir yang didederkan pada Pen-culture sebesar 84 – 86,67 % dengan rata-rata persentase kelangsungan hidup 85,33 % dan kisaran pertumbuhan berat tubuh sebesar 2,54 – 12, 97 gr dengan rara-rata pertumbuhan mutlak berat tubuh sebesar 6,77 gr. Kata kunci : Pendederan, Teripang pasir, Pen-culture

Using a head‐start conservation intervention to boost spawning numbers of the endangered Clanwilliam sandfish

AbstractFreshwater ecosystems are the most threatened on Earth, with many species facing extinction. The Clanwilliam sandfish (Labeo seeberi) is South Africa's most threatened migratory freshwater fish and is endemic to the Olifants–Doring River system in the Cape Fold Ecoregion. Non‐native fish predation and river desiccation have caused a recruitment bottleneck, severely compromising juvenile survival and resulting in a declining population of aging sandfish. The Saving Sandfish Project launched an emergency head‐start intervention in 2020 to reduce extinction risk. We (1) rescued juvenile sandfish from drying pools in a key spawning tributary (the Biedouw River); (2) relocated them to 6 off‐stream reservoirs; and (3) released reservoir‐reared sandfish back into their natal river once large enough to evade non‐native fish predation. Here, we estimate survival in the reservoir environment, evaluate return rates relative to wild run size, and assess the probability of return based on conditions at release. Between 2020 and 2022, we stocked 33,391 juvenile sandfish into the 6 reservoirs. After 1 year, the estimated survival rate at one reservoir was 0.679 (range based on 95% CI: 0.385–0.973). Release and return results are presented only for the first (2020) rescue cohort. In 2021, we released 1277 sandfish from 2 reservoirs into the Biedouw River, comprising 16.6% of the 2020 rescue cohort. Mean size at release was 169 mm (SE 0.6) total length. Of those released, 994 were PIT‐tagged. A total of 77 PIT‐tagged sandfish were recorded during the 2022 spawning migration—a return rate of 7.7% of tagged releases in the first year of returns. Size of fish and distance from the Doring River at release were significant predictors of return probability, with larger fish released further from the Doring experiencing a higher probability of return. This program serves as a model for the conservation of freshwater fish where there is an imminent and high risk of extinction.

Application of Sargassum sp extract on juvenile sandfish nursery

Sea cucumbers are a high-value fauna that can be found on Kei Island’s coastal area. Because of overexploitation and poor management, the sea cucumber population on Kei Island has declined dramatically. To solve this problem, the cultivation activities (breeding, nursery and growth out) of sea cucumbers need to be developed immediately. The aim of this study was to utilize the brown algae Sargassum sp to support the production of sandfish seeds in Household-Scale Hatchery. This study took place from April - May 2022 at Tual Teripang Center, Tual. Juveniles of sandfish are used as research objects with measuring between 3 - 15 mm in size and have a stocking density of 800 juveniles per tub. The feed used as treatment was included Sargassum sp extract 300 gr/tub (Treatment A), 400 gr/tub (Treatment B), and 500 gr/tub (Treatment C). Feeding has given every day and water changes was 50 - 60% per day. The calculation of growth and survival rate is the variable that observed in this study. As supporting data, water quality test measures were carried out. Three treatments have different effects on juvenile growth. The best result was obtained in Treatment C. For survival, showed all treatments had same effect on the survival rate of juvenile sandfish. It was concluded that Treatment C was better for the growth of juvenile sandfish than Treatment A and Treatment B.

Size-dependent predation on juvenile sandfish, Holothuria scabra by seagrass-associated crabs

Abstract High mortality of juvenile Holothuria scabra in seagrass nursery areas has been attributed to predation. In this study, laboratory and field experiments were conducted to determine the effect of the size of two seagrass–associated crabs, Thalamita crenata and Dardanus megistos, on the survival of juvenile sandfish at different sizes (1–10 g). Small juvenile sandfish (1–2 g) offered in field trials were more preferred by small Thalamita and large Dardanus. Non-lethal damage caused by both crabs were also evident, indicating differences in the mode of attack and consumption. The incidence of non-lethal wounds in medium and large juveniles in the laboratory indicate higher incidences of unsuccessful attacks by the crabs. Differences in consumption rate may be related to cheliped morphology and handling techniques, and activity patterns affecting encounter rates. Mortality rates of juvenile sandfish due to T. crenata (CW: 4.30–7.05 cm) ranged from 10–43%, while those by D. megistos (SL: 0.90–2.3 cm) was even higher at 34–53% after 24 h trials. This is the first report that a hermit crab D. megistos is a significant predator of juvenile sandfish. Results provide new insights on crab–soft-bodied prey interactions in tropical seagrass areas. These are also important considerations in stock restoration and ocean-based culture. Given that juveniles (≤10 g) are very vulnerable to predation by these common crab species, growing sandfish to larger sizes is essential prior to release in the field.

Characterization of digestive enzymes from sandfish, Holothuria scabra juvenile

Understanding the specific role of enzyme activity, such as digestive enzymes present in the intestine of Holothuria scabra juvenile, combined with an understanding of the animal habits and their digestive capacity is essential in the development of an appropriate diet. Juvenile sandfish with an average weight and total length of 2.81 ± 0.54 g and 4.10 ± 0.54 cm were collected and its intestine was used to analyze the activity of protease, amylase, and lipase enzymes. Parameters testing for all enzyme activities were conducted at 12 levels of pH (1.0; 2.0; 3.0; 4.0; 5.0; 6.0; 7.0; 8.0; 9.0; 10.0; 11.0; 12.0) and temperature 8 levels (10; 20; 30; 40; 50; 60; 70; 80; 90°C). Optimum pH for protease, amylase, and lipase activity were 7.0, 8.0, and 3.0, respectively, while optimum temperatures were 50, 50, and 40°C, respectively. This information about optimum pH and temperature in the biology of sandfish is useful as a basis for further studies on feeding physiology.

VARIATION OF TEMPERATURE AND ZEOLITE APPLICATION ON SIMULATED TRANSPORT OF CULTURED JUVENILE SEA CUCUMBER (Holothuria scabra)

Sea cucumber (Holothuria scabra) aquaculture practice required different sites for the juvenile and grow-out phase. While broodstock conditioning, spawning, and nursery phase were mostly conducted in an indoor hatchery, the juvenile needs to be reared outdoor in saltwater pond, sea pens, or ex-situ grow-out sites. However, information on optimal transport condition with regards to post-transport survival from the hatchery to the grow-out sites is limited. These gaps of knowledge required immediate research since the demand for sustainable sea cucumber culture is constantly increasing, whether for commercial or conservation (restocking) purposes. Therefore, the aim of this study is to investigate the effectiveness of transportation methods of juvenile sandfish by combining temperature and zeolite treatment. The variation of temperature (low and ambient) combined with the use of zeolite treatment on simulated transport condition of sea cucumber juvenile were evaluated in this study. This experiment used 3 (three) replicate groups consisting of 10 (ten) individual hatchery-produced sea cucumber juvenile (less than 0.1 g weight) held in 4 (four) different treatments of temperature and zeolite addition to medium water for 12 hours duration of simulated transport. The monitoring result of water quality (pH and ammonia) and the survival rate of sea cucumber juvenile observed within 7 (seven) days post-transport suggests that pH and survival rate were affected by the temperature regime and zeolite addition. The addition of zeolite and the increase of temperature tend to decrease pH values. However, the excessive decrease of temperature should be avoided during the transportation process as it tends to reduce the survival rate of sea cucumber juvenile.

Rate and Efficiency of Organic Carbon Assimiliation by Aquacultured Juvenile Sandfish Holothuria scabra

Diet assimilation rate is crucial to the growth and survival of Holothuria scabra juveniles during culture. To understand the assimilation rate and efficiency we assess organic carbon assimilation, which is closely related to the growth and source of variations in diet. We conducted a two-factor experiment, i.e., juvenile origin (cultured and wild H. scabra juveniles), and diet treatment (one control with no additional diet, and three additional diets, i.e., rice bran, dried cow manure, and seagrass Enhalus acoroides extract). We monitored the amounts of each diet that the juveniles consumed and the fecal pellets they egested. The diet, sediment, body walls, and organic carbon content of the fecal pellets were measured using an elemental analyzer combined with an isotope ratio mass spectrometer. Exponential growth was seen in the juveniles fed with rice bran, which had a fecal pellet egestion of 0.12–0.21 gC/d. Stable isotope analysis showed that the contribution of the diet proportion to the growth of the sandfish did not exceed 30%. The range of the assimilation rate was 35.3–62.4 gC/d. The average assimilation efficiency of organic carbon was 43.6 ± 27.7% (max 57.9%). Considering the assimilation rate and efficiency, we suggest a feeding interval of once every two days or twice per week at a rate of 3–5% of the total H. scabra biomass for a juvenile culture system.

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.

Factors affecting the spatio-temporal variability in the production of sandfish Holothuria scabra juveniles in floating hapa ocean nursery systems

Hatchery production of the tropical sea cucumber Holothuria scabra or sandfish has been successfully demonstrated in various countries, especially during the past decade. However, the main bottleneck in up-scaling production of larger sandfish juveniles is in the nursery phase where land-based facilities are limited in the Philippines compared to other countries. This has led to some promising pioneering research in ocean-based sandfish nurseries in the Philippines. However, site-specific and seasonal inconsistencies in production levels were observed. In this study, a comprehensive experiment comparing 17 replicated nursery culture operations of sandfish juveniles using floating hapas, was conducted across four sites with distinct geo-climatic zones in the Philippines and at different months from 2013 to 2016. We evaluated the performance of the ocean-based floating hapa nursery system by determining the effects of periphyton characteristics and broad-scale differences in meteorological variables to growth and survival of juvenile sandfish within different geo-climatic zones. Our data confirmed high spatial (across sites) and temporal (among trials within a site) variability in sandfish culture performances. Wind stress was the most significant driver of this variation, which negatively influenced growth and survival of juveniles especially during Cycle 1 (first 30 d). Sandfish growth was positively related to Chl-a and mean temperature, but was negatively impacted by Wind stress, Autotropic Index (AI), total rainfall (∑Rain), and sea-surface atmospheric pressure; while survival was positively affected by phaeophytin and Ash-Free Dry Weight (AFDW) content of the hapa biofilm. In Cycle 2 (succeeding 31–60 d), growth and survival was greatly influenced negatively by the re-stocked density (number of individuals surviving from Cycle 1), while survival was further affected negatively by ∑Rain and AFDW. Our results provide significant information on suitable ocean nursery conditions, periphyton/biofilm characteristics, and spatial-temporal considerations for optimizing production of H. scabra juveniles in floating hapas. We also highlight the negative effects of increasing biomass density when on-growing larger juveniles in this system. These insights are valuable in optimizing management and operation of ocean nurseries for sandfish, not only in various potential sites in the Philippines, but also in many developing tropical countries in the Indo-Pacific.

Utilisation of organic matter from Babylon snail (Babylonia areolata) culture sediments by cultured juvenile sandfish (Holothuria scabra)

The ability of sandfish to reduce organic matter in sediments from Babylon snail (Babylonia areolata) pond aquaculture in Vietnam was examined. Sandfish were cultured at low (25 in.. m−2, 43 g.m−2) and high (100 in.. m−2, 171 g.m−2) density in 500 l tanks provided with pond sediment or clean beach sand as a bottom substrate. A treatment that included pond substrate with no sandfish was included as a substrate quality control. Survival, weight gain, absolute growth (AGR) and specific growth (SGR) of sandfish, and total organic matter (TOM) and total nitrogen (STN) contents of the substrate were monitored over 56 days. No additional food was supplied to sandfish. Sandfish survival was similar between treatments (81–100 %). Significant interactions between substrate type and sandfish density were found for sandfish AGR (F1,8 = 7.84, P = 0.023) and SGR (F1,8 = 7.86, P = 0.023). Growth was most heavily correlated with sandfish density. AGR and SGR were greater when sandfish were cultured at low density on pond substrate (0.09 ± 0.03 g.day-1 and 2.59 ± 0.46 %.day-1, respectively). Mean individual sandfish weight gain in this treatment was 4.33 ± 1.31 g, an increase of 87.4 % compared to sandfish cultured on clean sand at the same density (2.31 ± 0.47 g). Growth of sandfish cultured at high density was poor, regardless of substrate type, with weight loss occurring in 4 of 6 high density treatment tanks. Organic matter content of substrates increased throughout the study in all treatments, however accumulation was significantly lower in tanks with sandfish. Sediment total N increased during the experiment but was significantly reduced in treatments with sandfish, compared to no sandfish. Although sandfish are unable to mitigate organic enrichment resulting from Babylonia culture, the results indicate that they derive significant benefit to growth from the enriched substrate.

Is culture performance of juvenile sandfish, Holothuria scabra, in ocean-based nursery systems influenced by proximity to milkfish (Chanos chanos) farms and hapa net mesh size?

The impacts of proximity to milkfish farms (i.e. ‘close’, ‘intermediate’ and ‘distant’) and different hapa net mesh sizes (i.e. 400 μm and 1 mm) on periphyton characteristics and growth performance of sandfish, Holothuria scabra, juveniles (4.6 ± 0.1 mm), were evaluated in a 30-day field experiment in the Guiguiwanen Channel at Bolinao, North-western Philippines. Growth and survival of sandfish juveniles were determined twice, and chlorophyll a and ash-free dry weight (AFDW) of periphyton were monitored every 5 days during the study. Opisthobranchs that recruited inside the hapa nets were identified and counted during monitoring. Survival of sandfish juveniles differed significantly between sites but was not influenced by mesh size by day 15. Survival was significantly higher at the intermediate site by day 15. Juvenile survival was significantly higher in 400 μm mesh hapa nets across all sites by day 30. Result showed that mean length and absolute growth rates (AGR) of sandfish juveniles were significantly influenced by mesh size but not by site at day 15. Juveniles reared in the 1 mm mesh hapa nets were larger and grew faster by day 15. However, by day 30, mean length and AGR of sandfish juveniles were significantly affected by site but not mesh size. Juveniles reared at the close site were significantly larger and grew faster than those reared at the intermediate site while mean length and AGR of juveniles reared at the distant site were not significantly different to those cultured at either the close or intermediate sites. Growth rates of juveniles were lower on day 30 compared to day 15 possibly resulting from reduced food availability, as indicated by lower periphyton AFDW, resulting from inter- and intraspecific competition. A positive correlation was found between AGR and the number of surviving sandfish juveniles by day 15, while no correlation between the two parameters was observed by day 30 indicating that reduced growth rates were not mediated by interspecific stocking density, but most likely resulted from high intraspecific grazing pressure. Chlorophyll a content of periphyton was higher during the second half of the experiment; however, total periphyton biomass (as AFDW) generally decreased overtime. This reduced food availability coincided with the higher number of opisthobranchs in the hapa nets by day 30. Results showed that sandfish juveniles can grow in an environment with varying levels of nutrient enrichment, however, areas close to mariculture activity may support improved growth because of resulting increases in periphyton biomass. Additionally, the use of finer mesh (400 μm) hapa nets positively impacted juvenile survival and would support earlier transfer of juveniles from the hatchery to the ocean reducing husbandry inputs and costs.

The Nursery Technique of Juvenile Sandfish, Holothuri scabra

Sea cucumbers are an Indonesian fisheries export commodity. Sea cucumber populations that are endangered in nature encourage sea cucumbers to be produced through hatchery and nursery. Through nursery, it is expected that sea cucumber juveniles are stronger and can increase survival rate when stocked in growth containers or restocked. This study aims to provide better sandfish nursery techniques and local area characteristics to support hatchery activities. This study was conducted in May - July 2018 at the Hatchery CV Pesona Manir Rat, Southeast Maluku Regency. Juvenile sandfish 30-36 days old, rearing in hapa measuring 100 x 100 x 70 cm with a density of 200 individuals/hapa. In one tank rearing is placed one hapa. During rearing, 100-150% of water is changed and given one-liter Navicular sp. every day. Aeration was installed 4 points on each hapa and water quality measurement was conducted every day. At the end of the study, body length measurements and mortality calculations were conducted. The result is that sea cucumber juvenile which is maintained has absolute growth ranging from 1.98 to 2.1 cm with an average absolute growth of 2.03 cm. The average mortality obtained was 53.83% with a range of 53% - 55%. Based on the discussion it was concluded that this technique can be applied in sandfish nursery. ABSTRAKTeripang merupakan komuditi eksport perikanan Indonesia. Populasi teripang yang terancam di alam mendorong teripang harus diproduksi melalui pembenihan dan pendederan. Melalui pendederan diharapakan anakan teripang lebih kuat dan dapat bertahan hidup lebih baik ketika ditebar pada wadah pembesaran atau direstoking. Penelitian ini bertujuan memberikan informasi teknik pendederan teripang pasir yang lebih baik dan berkarakteristik daerah setempat guna menopang kegiatan pembenihan. Penelitian ini dilaksanakan pada bulan Mei – Juli 2018 di Hatchery CV Pesona Manir Rat, Kabupaten Maluku Tenggara. Juvenil teripang pasir berusia 30 – 36 hari, dipelihara pada hapa berukuran 100 x 100 x 70 cm dengan kepadatan 200 individu / hapa. Pada satu bak pemeliharaan ditempatkan satu buah hapa. Selama pemeliharaan dilakukan pergantian air sebanyak 100 – 150 % dan diberikan satu liter Navicular sp. setiap hari. Aerasi dipasang sebanyak 4 titik pada setiap hapa dan dilakukan pengukuran kualitas air setiap hari. Diakhir penelitian, dilakukan pengukuran panjang tubuh dan perhitungan mortalitas. Hasilnya juvenile teripang yang dipelihara mengalami pertumbuhan mutlak berkisar antara 1,98 – 2,1 cm dengan rata-rata pertumbuhan mutlak sebesar 2,03 cm. Mortalitas rata-rata yang diperoleh sebesar 53, 83 % dengan kisaran 53 % - 55 %. Berdasarkan pembahasan disimpulkan bahwa teknik ini dapat diterapkan dalam pendederan teripang pasir.

Nursery culture of sandfish Holothuria scabra in sea-based floating hapa nets: Effects of initial stocking density, size grading and net replacement frequency

Sea-based culture of early juvenile sandfish Holothuria scabra up to fingerling size (>2 g) using floating hapa nets has been confirmed as a viable nursery system in tropical countries such as the Philippines. However, production can be further optimized through more efficient rearing practices. In this study, we demonstrate the effects of initial stocking density, size grading and net replacement frequency during the culture of early juvenile sandfish in sea-based floating hapa nets (2 × 1 × 1 m). Testing different initial stocking density treatments ranging from 150 to 2000 early juveniles (4–10 mm; 0.02–0.06 g) per hapa net, we confirmed significantly faster growth (0.06–0.08 g d−1) and higher survival (72–97%) in low densities (≤500 hapa−1), compared to high densities (≥700 hapa−1: 0.02–0.04 g d−1; 67–80%). Low density culture can produce 2 g sandfish in about a month, while higher densities will require a 2–3 mo culture period to reach this size. Culture performance following size grading was also compared using three initial size classes (small, 0.05–0.99 g; medium, 1–1.99 g; and large, 2–3 g) and a mixed group (0.05–3.00 g). At 45 d, juveniles in pooled size-graded groups grew significantly faster (0.11–0.13 g d−1) than those in the mixed group (0.01 g d−1). Survival was significantly higher in the medium (85.3%) and large (84.7%) groups, than those in the small (54.4%) and mixed (45.6%) groups. However, size variation was not significantly mitigated by grading during the 45-d culture. Culture performance of sandfish was not significantly enhanced by more frequent net replacement for short-term rearing (30–45 d). Optimal results were gained from an initial stocking density of ≤500 early juveniles (5–10 mm) per floating hapa net which may be cultured in a month, without requiring net replacement and size grading to produce ≥2 g sandfish. However, in cases of high hatchery production, it is also feasible to adopt higher density stocking (e.g. >1000 hapa−1), but will require longer culture duration (60–85 d), monthly net replacement and size-grading to attain the same size. Results of this study can help fine-tune management practices for nursery culture of sandfish in sea-based floating hapa net nurseries in order to boost production of fingerlings needed for aquaculture and restocking.

Social and economic challenges to community-based sea cucumber mariculture development in New Ireland Province, Papua New Guinea

This article describes the outcomes of research into the potential of community-based mariculture of the commercial sea cucumber, sandfish (Holothuria scabra), as a sustainable livelihood in New Ireland Province, Papua New Guinea (PNG). Around 5000 cultured juvenile sandfish were stocked in a 5-ha trial community sea ranch. The community agreed to protect the area from fishing until researchers collected technical data on sandfish performance. However, poaching of sandfish from the trial sea ranch occurred during the 2018 annual sea cucumber fishing season and no technical data were generated. Community attitudes and responses to the fishing season, the mariculture research activity and the failure of the trial sea ranch were investigated. Widespread community approval of the trial sea ranch and respect for the fishing prohibition were reported. However, it was found that poaching within the ranch escalated to extensive fishing because community-based management proved inadequate to sanction the poachers. Increased buying pressure and higher prices led to intensified fishing effort in the 2018 season. The trial sea ranch failed due to external pressures (i.e., brief, intense fishing season; limited project capacity), compounded by internal factors (i.e., weak local leadership; community disunity). It was concluded that research into and development of sandfish mariculture as a livelihood option in New Ireland Province might be impossible at this time due to the high value of sandfish, the annual sea cucumber fishing season, and ineffective governance at community, provincial and national levels. Lessons learned from this experience are presented and alternative models discussed.

Effects of sediment enrichment with macroalgae, Sargassum spp., on the behavior, growth, and survival of juvenile sandfish, Holothuria scabra

To scale-up culture production of the sea cucumber Holothuria scabra using ocean grow-out systems, bottlenecks in enhancing the growth and survival of juveniles need to be addressed. As the selection of release sites is fraught with uncertainty, organic enrichment of sediment using dried Sargassum spp. to increase food abundance (i.e., microalgae and bacteria) may be a viable option to optimize ocean nursery systems. The effects of sediment enriched with dried Sargassum spp. on the diel burying behavior, growth, and survival of juvenile (>3 g) sandfish were investigated in the field for 60 days using sea pens (2.25 m2) with a stocking biomass of 66 g m−2, and in glass tanks (0.045 m2) with the same stocking biomass (∼3 g individual tank-1) in the laboratory for 30 days. Enrichment with Sargassum markedly changed sediment characteristics. Although diurnal burying behavior did not vary significantly between treatments, a greater percentage of juveniles in enriched pens and tanks remained buried during the daytime compared to unenriched pens. Without protection from predators in the wild, all juveniles from enriched pens survived compared to those from unenriched pens (85 ± 10%) after 7 days. After 30 days, absolute growth rates (AGR) of juveniles in enriched pens (0.51 ± 0.06 g day-1) and tanks (0.82 ± 0.27 g day-1) were significantly higher compared to unenriched pens (0.13 ± 0.04 g day-1) and tanks (0.49 ± 0.19 g day-1). Results showed that mean sediment chlorophyll-a content of ∼4 μg g-1 in sea pens enriched with Sargassum spp. could hasten the growth of ∼3 g juveniles to >20 g in 30 days. This study demonstrated that the organic enrichment of sediment is a viable option to optimize the growth of sandfish in an advanced ocean nursery system that may significantly improve survival prior to release for grow-out.

No Difference in Nutritional Profiles of Wild and Cultured Juvenile Sandfish, Holothuria scabra

No Difference in Nutritional Profiles of Wild and Cultured Juvenile Sandfish, Holothuria scabra

Successful large-scale hatchery culture of sandfish (Holothuria scabra) using micro-algae concentrates as a larval food source

This paper reports methodology for large-scale hatchery culture of sandfish, Holothuria scabra, in the absence of live, cultured micro-algae. We demonstrate how commercially-available micro-algae concentrates can be incorporated into hatchery protocols as the sole larval food source to completely replace live, cultured micro-algae. Micro-algae concentrates supported comparable hatchery production of sandfish to that of live, cultured micro-algae traditionally used in large-scale hatchery culture. The hatchery protocol presented allowed a single technician to achieve production of more than 18,800 juvenile sandfish at 40days post-fertilisation in a low-resource hatchery in Papua New Guinea. Growth of auricularia larvae fed micro-algae concentrates was represented by the equation length (μm)=307.8×ln(day)+209.2 (R2=0.93) while survival over the entire 40day hatchery cycle was described by the equation survival=2×day−1.06 (R2=0.74). These results show that micro-algae concentrates have great potential for simplifying hatchery culture of sea cucumbers by reducing infrastructural and technical resources required for live micro-algae culture. The hatchery methodology described in this study is likely to have applicability to low-resource hatcheries throughout the Indo-Pacific and could support regional expansion of sandfish hatchery production.

Viability of a bottom-set tray ocean nursery system for Holothuria scabra Jaeger 1833

Scaling up the hatchery production of juvenile sandfish Holothuria scabra is constrained by limited hatchery space and the associated high operational costs. To shorten the hatchery rearing phase, ocean nursery systems like floating hapa nets have been used with good prospects but with limitations during rough sea conditions. In this study, the potential of bottom-set trays (0.14 m2) as an alternative ocean nursery system for early sandfish juveniles (0.5 ± 0.1 cm) was evaluated. The effects of stocking density and presence of artificial substrates (AS) on the growth and survival were determined in a 60-day field experiment. Average length and growth rates at lower stocking density treatment (100 individuals tray−1) were significantly higher (1.45 ± 0.22 cm; 0.03 ± 0.01 cm day−1) than at higher stocking density treatments (400 and 500 individuals tray−1) 0.95 ± 0.06 cm; 0.03 ± 0.004 cm day−1) with or without AS (p < .05) respectively. The coefficient of variation in length (CV) at high stocking densities were significantly higher than at low densities (p < .05) and growth rate was strongly negatively correlated with density. Survival was significantly higher (55% ± 9%) in trays with AS across all stocking density treatments than in trays without AS (34% ± 2%). Results suggest that AS may have reduced intra- and interspecific interactions, resulting to significantly lower growth variations and higher survival. The bottom-set tray with AS can be a practical alternative ocean nursery unit for rearing early sandfish juveniles particularly when the sea surface condition is rough. With improved design and density management, survival and growth may be further enhanced.