Nursery Culture Research Articles

Survival and growth performance the catfish Clarias gariepinus in high density nurseries using recirculating aquaculture system (RAS)

The recirculating aquaculture system (RAS) is a cultivation system that minimizes water changes and can optimize high stocking densities (SD). The purpose of this study was to determine the effect of nursery culture in high stocking density with RAS on survival rate (SR), specific growth rate (SGR), relative length (LR), weight gain (WG), length gain (LG)and feed utility efficiency (FUE) of juvenile catfish. The study used a completely randomized design with 4 treatments and 3 replications: R3000 (SD of 3,000 fish/m2 with RAS); NR3000 (SD of 3,000 fish/m2 without RAS); R4000 (SD of 4,000 fish/m2 with RAS); NR4000 (SD of 4,000 fish/m2 without RAS). Juvenile catfish measuring 3.3±0.2 cm were reared for 21 days and water changes were carried out every 2 weeks in the RAS and every 2 days in the non-RAS. The results showed that the SR was not significantly different for all treatments. The highest SGR, LR, WG, LG and FUE were shown in the R4000 treatment (p<0.05). Water quality parameters, especially total ammonia nitrogen in the RAS treatment had a lower value than without RAS. The abundance of total bacteria in the RAS treatment was more than without RAS. This study showed that the density of 4,000 fish/m2 with the RAS was able to provide better catfish nursery production performance than without RAS.

Improved survival and growth of silver therapon Leiopotherapon plumbeus early juveniles through co‐feeding with Artemia and commercial feeds

This study examined the effects of co-feeding Artemia and commercial feeds on survival, growth and fatty acid composition of silver therapon Leiopotherapon plumbeus early juveniles. Triplicate groups of 36 days post hatch (DPH) early juveniles (17.09 ± 1.69 mm; 0.07 ± 0.02 g) were stocked in nine glass aquaria at 25 individuals per aquarium and reared for 60 days on three feeding regimes: (A) Artemia + powdered commercial tilapia feed (35% crude protein (CP)); (B) Artemia + powdered commercial prawn feed (38% CP); and (C) Artemia nauplii only as the control group. Early juveniles co-fed Artemia and commercial feeds had significantly higher survival (97%) than those fed Artemia alone (86%). Except for the condition factors that were similar to the control group, higher mean total length (30.2 ± 1.3 mm and 27.6 ± 1.2 mm), body weight (401 ± 64 mg and 339 ± 46 mg), length- (SGRL; 0.95 ± 0.07%/day and 0.80 ± 0.07%/day) and weight-specific growth rates (SGRW; 2.85 ± 0.27%/day and 2.58 ± 0.22%/day) were also observed in the co-feeding groups, independent of protein, fat and other nutrient levels in commercial feeds. Higher levels of long-chain polyunsaturated fatty acids were reflected in early juveniles co-fed Artemia and commercial feeds than those fed exclusively on Artemia contributing, in part, to the higher growth and survival observed in the co-feeding groups. Together, these results suggest that co-feeding strategy showed best results in terms of growth and survival, and that commercial feed with 35% protein and 6% crude fat levels may be beneficial in supplementing live feed with essential nutrients to optimize production of silver therapon fry during nursery culture.

Effects of artificial substrates on the growth and immunology of postlarvae of Marsupenaeus japonicus (Spence Bate, 1888) (Decapoda: Dendrobranchiata: Penaeidae) reared in biofloc

Abstract We investigated the effects of biofloc and artificial substrates (net and brush) on the growth and immunology of the postlarvae of Marsupenaeus japonicus (Spence Bate, 1888) reared for 30 days. The mRNA expressions of innate immune-related genes (prophenoloxidase, masquerade-like serine proteinase, and lysozyme) in the postlarvae were analyzed using quantitative reverse transcription PCR (qRT-PCR). The highest specific growth rate of larvae (3.66 ± 0.02% d–1, 3.75 ± 0.02% d–1) were shown in the net and control groups. The highest survival rate (90 ± 7.1%) was observed in the brush group (P < 0.05). The net yield was significantly higher in the artificial substrate groups (brush 36.60 ± 6.19 g m–2, net 36.46 ± 2.36 g m–2) than in the control (33.79 ± 0.16 g m–2) (P < 0.05). Total suspended, volatile suspended, and suspended solids were significantly lower in the brush group than in the other groups. The immune-related genes showed significantly higher expressions in the artificial substrate groups than in the control. These results support the benefits of artificial substrate in M. japonicus nursery culture to mitigate space competition and suppress cannibalism, with a positive effect on survival. The additional surface area provided by the biofloc, which the larvae can graze on, enhanced the expression of immune-related genes in individuals.

The loss of seed mussels in longline aquaculture

AbstractThe substantial loss of seed mussels during the early stages of longline aquaculture—often exceeding 95%—is a major issue that erodes the security and profitability of production while limiting the sustainable expansion of this industry in many parts of the world. There are many biological, environmental and procedural factors that potentially cause seed losses. The present understanding of these factors is highly limited, based on disparate lines of evidence and constrained by the challenges associated with quantifying the fate of minute organisms in the field. Addressing these knowledge gaps is a prerequisite for meeting the growing global demand for farmed seafood and requires significant and coherent research. We identify the diverse range of potential drivers of seed loss in mussel aquaculture and review existing knowledge around these factors to identify critical knowledge gaps and research priorities. Losses appear to be caused by a complex suite of interacting factors that include stress during transfer between regions, underlying variations in seed condition, change in the farm environment, predation, competition from biofouling organisms and migratory behaviour of seed mussels. Solutions to the losses of mussel seed in commercial culture are mostly likely to be achieved through research directed at evaluating a range of practical interventions during the critical phase of nursery culture of mussel seed.

Investigation of the potential of liposome and microparticulate feeds to partially replace microalgae in the nursery rearing of green‐lipped mussels ( Perna canaliculus )

The seeding of small juvenile green-lipped mussels (Perna canaliculus) onto coastal farms is associated with high losses. These losses can be reduced by seeding larger juveniles; however, the nursery culture of juveniles is unviable because of the high cost of producing live microalgal feeds. In this study, we compared the ability for two diets, a formulated microparticulate feed, MySpat and liposomes fabricated with mussel extract to replace live microalgae at different proportions for feeding small (1.9 mm shell length ±0.02 SE) green-lipped mussels. The experimental diets consisted of a mix of live Tisochrysis lutea, Diacronema lutheri and Chaetoceros muelleri that were replaced with increasing proportions of MySpat (25%, 50% and 75%), and liposomes (25% and 50%). There were no significant differences in mortality of mussels relative to the control (100% microalgae) among any of the diet treatments. However, mussel growth tended to decrease with increasing substitution of the microalgal component of the diets. The results from this study suggest that microparticulate and liposome formats provide a viable mode of food delivery to juvenile mussels, with improved formulation of these formats having the potential to lead to the substitution of live microalgal diets which make nursery culture unviable at present.

A Review of the Nursery Culture of Mud Crabs, Genus Scylla: Current Progress and Future Directions.

Simple SummaryNursery culture knowledge is important for successful commercial seed production especially for mud crab, genus Scylla, a highly valued delicacy. The aim of this review paper is to summarise the status and information on the current nursery culture stage of the mud crab. Various aspects of mud crab hatchery described in this paper are expected to facilitate practitioners and lay people to easily understand a mud crab nursery. This review also provides guidelines for researchers in conducting future research and development on a mud crab nursery in order to increase the production of mud crab crablets for the farming industry.The nursery stages of mud crab, genus Scylla, proceed from the megalopa stage to crablet instar stages. We review the definition and several of the key stages in mud crab nursery activities. The practice of the direct stocking of megalopa into ponds is not recommended due to their sensitivity. Instead, nursery rearing is needed to grow-out mud crabs of a larger size before pond stocking. Individual nursery rearing results in a higher survival rate at the expense of growth and a more complicated maintenance process compared with communal rearing. The nursery of mud crabs can be done both indoors or outdoors with adequate shelter and feed required to obtain a good survival percentage and growth performance. Artemia nauplii are still irreplaceable as nursery feed, particularly at the megalopa stage, while the survival rate may be improved if live feed is combined with artificial feed such as microbound diet formulations. Water quality parameters, identical to those proposed in tiger shrimp cultures, can be implemented in mud crab rearing. The transportation of crablets between different locations can be done with or without water. The provision of monosex seeds from mud crab hatcheries is expected to become commonplace, increasing seed price and thus improving the income of farmers. Numerous aspects of a mud crab nursery including nutrition; feeding strategies; understanding their behaviour, i.e., cannibalism; control of environmental factors and practical rearing techniques still need further improvement.

Digestive system and growth performance of giant gourami ( Osp hronemus goramy Lacepede) juveniles in biofloc systems fed with different feed types

This research aimed to evaluate the effects of aquaculture systems and types of feed on the digestive system and the growth performance of Giant gourami Osphronemus goramy juveniles. This research used two experimental factors (2 × 3), that is culture systems (biofloc and control systems) and feed types (artificial feed, Tubifex worm and a combination of both feed). The experiment comprised of six treatments in triplicates, that is artificial feed in biofloc system (BP), Tubifex worm in biofloc (BW), combined feed in biofloc system (BCo), artificial feed in control system (CP), Tubifex worm in control system (CW) and combined feed in control system (CCo). Gourami juveniles with an average body weight of 0.03 ± 0.01 g were randomly distributed into 18 units of aquarium (18 L) at a density of 5 fish/L. Feeding was done to apparent satiety, four times a day. The fish in treatment BCo showed higher protease activity, villi length and surface area than those of other treatments (p < 0.05). Both the culture system and types of feed had significant effects (p < 0.05) on the growth performance of giant gourami juveniles. The fish survival was more affected by the types of feed rather than the culture systems, in which the treatment with artificial feed (P) had the lowest survival compared to the other treatments. In conclusion, nursery culture in biofloc system fed with a combination of artificial feed and Tubifex worm (BCo) could improve the digestive and growth performance of giant gourami juveniles.

Nursery and grow-out culture of the abalone Haliotis asinina on a reef flat: A comparison of growth and survival using different culture containers

The study was conducted to compare four different culture containers [cage, recycled oil container, tray (control), and tube] in the nursery and grow-out culture of the abalone Haliotis asinina on a reef flat. For nursery culture, early juvenile abalone with mean shell length (SL) of 1.30 ± 0.006 cm and mean body weight (BW) of 0.45 ± 0.007 g were stocked in the containers at 100 ind m−2 and reared until they attained the 3 cm SL size required for grow-out culture in three of the four culture containers. For grow-out culture, juvenile abalone harvested from nursery culture with mean SL of 3.23 ± 0.018 cm and mean BW of 7.33 ± 0.131 g were stocked in the containers at 50 ind m−2 and reared until they were harvestable at 5 cm SL cocktail size in three of the four culture containers. The 3 cm SL grow-out size was attained at 90 days of culture (DOC) in recycled containers, trays, and tubes, while the 5 cm SL cocktail size at 180 DOC in the same containers. Abalone reared in tubes had the highest mean SL after 90 DOC in nursery culture (3.21 cm), while those in trays after 180 DOC in grow-out culture (5.30 cm). However, at the end of the nursery and grow-out culture, there were no significant differences in mean SL among the abalone reared in these three culture containers. In both culture phases, abalone reared in cages had the lowest mean SL, 2.88 and 4.44 cm, respectively. Survival was highest in trays (98.64%) during nursery culture and in tubes (96.57%) during grow-out culture. With comparable results in recycled containers, trays, and tubes for both growth and survival at the nursery and grow-out phases, tubes are recommended for use when culture is to be done on reef flats. Tubes are the most stable and durable among the four culture containers tested. They can withstand strong winds and waves and may be reused for several culture runs.

Experiment on compaction of air-dried soil under drop shocks.

For the requirement in container nursery culture that growing media should be achieved the appropriate degree compaction, this paper presents an experiment on the compaction dynamics of air-dried soil under repetitive drop shocks, as a preliminary step toward the mechanization of this compaction method. The drop height used to adjust the shock intensity included 2 mm, 4 mm, 5 mm and 6 mm. And the overall packing density of soil in a vertically stratified cylinder vessel and the local packing density in each layer were taken as indicators of soil compaction states. The stretched exponential function derived from KWW law than the empirical inverse-logarithmic function has been found to be more suitable for expressing the temporal evolution of soil compaction, according to the results of curve-fitting to test values of the overall and local density. It is inherent in this experimental configuration that the drop shock intensity even at a constant drop height varies with drop times, owing to the interaction between the soil packing itself and drop shocks caused by the combination of the packing and the container. But the function t/τf(t,H) is manifested as a straight line on the drop times t with the line slope related to the drop height H, so the soil compaction dynamics caused by its drop shocks and that under the condition with actively controlled intensity actually share the common relaxation law. In addition, the soil's one-dimensional distribution of local packing density showed a slight positive gradient as similar as monodisperse particles did.

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.

Evaluation of a floating upwelling system for nursery culture of the Greenshell ™ mussel (Perna canaliculus)

Major losses of early juvenile seed mussels or spat are a typical feature of the aquaculture production cycle for many mussel species. These losses are caused by a variety of factors including predation, mortality, and the innate migratory behaviour of spat. In this study, we examined the potential to reduce spat losses by using a floating upwelling system (FLUPSY) for raising the spat of New Zealand's Greenshell™ mussel (Perna canaliculus) to a larger size before transfer to a coastal mussel farm. The losses of spat experimentally cultured within a FLUPSY over 85 days were much lower compared to spat that were seeded directly into coastal waters (78% vs. 99.8%). At the end of the 85-day nursery culture period, spat in the FLUPSY were 7% larger despite being cultured at higher densities. The losses for two size classes of spat that were raised in the FLUPSY remained relatively high (83% and 95% for spat seeded out at 6.6- and 15.5-mm shell length (SL) respectively) after two months of being experimentally seeded onto a coastal mussel farm. However, these losses are lower than have been reported previously for this species during this stage of production. The results from this study suggest that the addition of a FLUPSY nursery stage to the Greenshell™ mussel production could greatly reduce spat losses and improve production efficiency.

Effects of truffle inoculation on a nursery culture substrate environment and seedling of Carya illinoinensis

We inoculated Tuber aestivum and Tuber sinoaestivum on Carya illinoinensis to explore the effects of inoculation on host plant growth, enzyme activities, the physicochemical properties of rhizosphere soil, the denitrifying bacterial community in the rhizosphere, and the distribution of mating type genes in the rhizosphere. We found that the Tuber spp. inoculation increased the height of the host plant and that the stem circumference of the host was greater two months after inoculation. Six months after inoculation, the peroxidase activity of the seedlings inoculated with T. sinoaestivum was higher than that of the control. At four and six months after inoculation, the superoxidase dismutase activities of the seedlings inoculated with T. aestivum were higher than those of the seedlings inoculated with T. sinoaestivum. Six months after inoculation, nitrate nitrogen content was lowest in the control and highest in the T. sinoaestivum treatment. Among the nirS-type denitrifying bacteria community, the relative abundances of Proteobacteria were high. T. aestivum and T. sinoaestivum inoculation did not affect the diversity of denitrifying bacteria. The mating type genes MAT1-1-1 and MAT1-2-1 were detected in the rhizosphere of C. illinoinensis inoculated with T. sinoaestivum and T. aestivum, and MAT1-1-1 dominated over MAT1-2-1.

Effects of carbon sources on the culture of giant river prawn in biofloc system during nursery phase

A six-week nursery culture of giant river prawn Macrobrachium rosenbergii was conducted in a zero-water exchange biofloc technology (BFT) system. Water quality, microorganisms, proximate composition and growth performance of prawn were compared by using five different carbon sources: wheat bran (WB), rice flour (RF), molasses (MO), maize starch (MS) and palm kernel expeller (PKE). These carbon sources were added at a carbon-nitrogen ratio of 15:1. Fifteen 125 L polyethylene tanks with water volume of 100 L were used for this experiment. Each tank was stocked with 100 postlarvae (average initial weight 21.9 ± 2.3 mg). Each treatment was randomly assigned in triplicate. The water quality parameters viz. temperature, pH, dissolved oxygen and ammonia-N did not differ (P > 0.05) among five different carbon treatments. MO based BFT system had significantly (P < 0.05) lowest nitrite-N and the highest biofloc volume than other treatments. The postlarval survival (88.6 %) was significantly higher (P < 0.05) in MS treatment and followed by RF (73.0 %), MO (68.3 %), WB (61.0 %) and PKE (56.3 %) treatments, respectively. Significantly (P < 0.05) better FCR (2.21) was obtained in MS treatment. The final weight, weight gain and specific growth were similar (P> 0.05) among the five treatments. Higher gross return, net return and benefit-cost ratio were obtained in MS group than WB, MO and PKE. Significantly (P < 0.05) the highest lipid (1.97 % dry weight) was obtained in MS bioflocs and followed by RF, WB, MO and PKE bioflocs, respectively. The present study indicated that MS carbon source for biofloc technology enhanced M. rosenbergii postlarval survival and growth.

Optimum Salinity for Growth of Tropical Eel Anguilla marmorata Quoy &amp; Gaimard, 1824 in Nursery Culture

Optimum Salinity for Growth of Tropical Eel Anguilla marmorata Quoy &amp; Gaimard, 1824 in Nursery Culture

Fertilización de Pithecellobium dulce (Roxb.) Benth en vivero: efectos en la calidad de planta

La fertilización en vivero es una práctica cultural con potencial para mejorar la calidad de planta, pero es necesario definir niveles de fertilización adecuados para cada especie. Este estudio evaluó el efecto de niveles de fertilización en la calidad de planta de Pithecellobium dulce, durante la etapa de vivero. Los niveles aplicados fueron nueve; consistieron en regímenes en los que se combinó un fertilizante de liberación controlada (FLC) 18-6-12, en tres dosis (4 g L-1, 6 g L-1 y 8 g L-1 de sustrato) con un fertilizante hidrosoluble (FHS) 20-20-20, en concentraciones de nitrógeno de 0 mg L-1, 75 mg L-1 y 150 mg L-1. El efecto de los regímenes de fertilización se determinó analizando índices morfológicos de calidad, tasas de asimilación neta (TAN) y estado nutrimental N-P-K en plantas de cuatro meses de edad. Una prueba de calidad fue diseñada para someter a las plantas a estrés en una condición de escasa fertilidad y pérdida de biomasa aérea, para evaluar capacidad de rebrote y crecimiento. Hubo diferencias estadísticas por efecto de los regímenes de fertilización. En general, la combinación de 8 g de FLC con 150 mg de nitrógeno por litro del FHS propició un incremento en la calidad morfológica y en la TAN de las plantas, aunque nutrimentalmente las respuestas principales fueron de suficiencia y dilución. En la prueba de calidad, las plantas tuvieron limitaciones para favorecer su rebrote o crecimiento según la cantidad de reservas nutrimentales. La fertilización con FLC y FHS tiene potencial para incrementar la calidad de planta de P. dulce en vivero.

Effect of dietary graded levels of astaxanthin krill oil and high protein krill meal on the growth performance and stress resistance of post larval Litopenaeus vannamei under hyper‐intensive nursery culture

Effect of dietary graded levels of astaxanthin krill oil and high protein krill meal on the growth performance and stress resistance of post larval <i>Litopenaeus vannamei</i> under hyper‐intensive nursery culture

Emersion and relative humidity control resettlement success of juvenile marine mussels

The successful resettlement of marine mussels is an essential but overlooked process in their early life. A major challenge facing the mussel aquaculture industry is the extreme inefficiency of the seeding process, with most mussels being lost soon after seeding due to mortality or secondary settlement behaviour. Extended periods of nursery culture have been proposed as a method to reduce these losses by culturing juveniles to a larger size. The ability of mussels to resettle to suitable aquaculture structures is critical to the success of nursery culture. This study assessed the ability of juvenile mussels (Perna canaliculus) to resettle to a commonly used aquaculture substrate (coir ropes) following emersion (0−20h) and variations in relative humidity (RH), stressors that are intrinsic to the transfer of mussels among aquaculture sites. Across the experiments, increased emersion time either reduced or slowed resettlement success. Increases in RH had strong positive effects on the resettlement success of juvenile mussels even at long emersion durations (20h). Low (~ 40%) and mid (~ 60%) RH reduced resettlement to <7.1% ± 3.5 SE after a 5-h emersion compared to 61.7% ± 3.2 SE in samples held at high (>90%) RH. Staining procedures indicated that mussels failing to resettle after longer emersion and low RH treatments were non-viable. Aquaculture operators should strive for high RH conditions and shorter emersion durations whenever their juvenile mussels are emersed. If these conditions can be achieved, the results of the study suggest that juvenile mussels can be successfully resettled for use in aquaculture, representing a first step toward extended nursery culture and a more efficient use of juvenile mussel resources.

Effects of low and high pH on sea urchin settlement, implications for the use of alkali to counter the impacts of acidification

Respiration, photosynthesis, and calcification of cultured organisms and biological substrata can substantially alter the pH and other carbonate parameters of water in aquaculture systems. One such example is the diel cycle of photosynthesis and respiration by diatoms and seaweeds growing on ‘settlement plates’ used to induce metamorphosis of invertebrate larvae and as food for post-larvae. We documented low pH and high pH conditions in nursery raceways and simulated settlement tanks that were as much as 0.26 pH units lower and 0.52 pH units higher than the pH of the source seawater supplied to the systems. To better understand whether the low pH and high pH conditions commonly found in aquaculture culture systems affected the success of the settlement stage of the sea urchin Centrostephanus rodgersii, we induced larvae to settle at pH 7.6, 7.8 (created by injecting CO2), 8.1 (ambient), 8.2, and 8.3 (created by raising total alkalinity), and followed post-settlement growth, development, and survival for 16 d. At metamorphosis, low pH significantly increased the occurrence of abnormalities and reduced the number and length of the sea urchins' spines and pedicellaria, but did not affect settlement rate or size compared to ambient pH. In contrast, high pH generally had little effect on morphological traits, but settlement was significantly reduced by 14–26% compared to ambient and low pH treatments. After 16 d, juveniles in the low pH treatments were as much as 7% smaller, had 2–4 fewer and 9–13% shorter spines, and had less-developed digestive systems compared to juveniles in ambient or high pH treatments, and there was a non-significant trend towards lower survival in low pH treatments. Our results highlight that the low pH and high pH conditions in invertebrate settlement and nursery culture systems have the potential to hamper production through reduced settlement or growth rates. We need to understand the impacts of fluctuating pH in culture systems, especially day-night oscillations. Treating seawater with alkali chemicals to stabilise pH and counter acidification should be done with caution. Due to the potential for deleterious effects on settlement, dosage regimens will need to be optimised.

Development of nocturnal feeding and photosensitivity in early juveniles of the warty sea cucumber Stichopus cf. horrens

Behavioral responses to light of early life stages provide insights on the development of photosensitivity in nocturnal species such as Stichopus cf. horrens. In this study, the onset of nocturnal feeding behavior, growth, and survival during early juvenile development (0.56 ± 0.16 cm; 47 days post-settlement) of the species were investigated for 30 days, in the presence (S) or absence (W) of artificial shelters and under three light regimes: constant light (24 L), constant dark (24D), and a 12 -h light, 12 -h dark period (12 L:12D). Juveniles in all treatments fed initially during daytime hours but eventually exhibited a shift to nocturnal feeding by day 11. This behavioral shift to nocturnality was delayed among individuals under constant dark conditions. Continuous light exposure without shelter resulted in low juvenile survival and mass mortality in some replicates of the treatment. In contrast, growth and survival were highest for juveniles in constant dark. This study showed the endogenous control of feeding in this species. It also demonstrated that growth increases significantly when early juveniles are reared with shelters or in constant dark. Optimizing the light regime and type of shelter can improve food accessibility and juvenile growth without hindering the development of photosensitivity in early juveniles. Further studies are needed to enhance the nursery culture of this species.

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.