That's why we call them "sea cucumbers" or sea cucumbers. Sea cucumber mariculture can provide a good livelihood option for coastal communities while protecting remaining wild stocks.
The sandfish ( Holothuria scabra )
Physical characteristics
Behavior, feeding, and defense
Other than burrowing in sediments, sandfish don't have much defense against predators. Predators such as crabs, shrimp and fish will then ingest the expelled organs as the sandfish crawls and burrows into the sediment.
Reproduction and life cycle
In another week or two, the young sea cucumbers will migrate to the sediments and forage into deeper areas as they grow and mature. The overall design and cost of the hatchery depends on the size of the production target and budget.
Location and structural layout
These can also be used as primary nursery rearing tanks where fine mesh step sack nets can be hung. used as food for juveniles of established sandfish.
Facilities, equipment and technical manpower
- Primary seawater intake system
- Secondary seawater pump, sand filter tank, and reservoir
- Microfilter array and UV sterilizer
- Aeration lines and air filters
- Microscopes and implements
Seawater that will be used for the spawning tanks, larval rearing tanks and algae culture tanks must be as clean as possible. There are some locally available concentrated products or "pastes", but these have not been very well tested and verified to be used for sandfish hatchery production.
Microalgae species for larval sandfish
Hatchery production mainly involves rearing larvae of target aquaculture species in ponds.
Live culture of microalgae in the hatchery
Initial culture of microalgae to 10 L
Due to the larger volume required for the commercial fertilizer solution, it is practical to prepare 20 liter batches of this medium. During use, 1 ml of this fertilizer solution is required for every 1 liter of microalgae grown.
Field collection, selection, transport
Collect broodstock from intertidal shores. Suitable sites for sandfish collection are flat intertidal shores with sandy-muddy to coarse sediments and
Schedule collection when low tide occurs late afternoon or early evening
Select broodstock that are preferably more than 400 g and with no signs of parasites and
Make sure that a proportional number of
Pack sandfish in polyethylene bags and place in styrofoam boxes for transport
Broodstock conditioning
Acclimate the collected broodstocks to the water conditions in the hatchery. Upon arrival from the field, allow acclimation of the animals to the
Stock broodstock from different batches separately. A new batch of broodstock should not be mixed with other prior batches, especially when they
Maintain natural food and provide supplemental feeding to broodstocks
Spawning induction
Allow broodstocks to defecate overnight prior to spawning. A
Sandfish can respond to thermal and food stimulation at any time of day, but the most convenient time for spawning may be early in the morning when the water temperature is relatively low. During thermal stimulation, the temperature of the water in the spawning tank increases by 3-5 °C higher, the temperature of the water in the spawning tank increases by 3-5 °C higher than the ambient temperature. To do this, the water level in the spawning tank is first reduced to 10-15 cm (from 40-50 cm) to reduce its volume for faster heating.
Usually in the Philippines, the ambient water temperature in the morning (7–9 am) can be between 26 and 29 °C. While waiting for spawning to occur, it is important not to disturb the sandfish in the tanks further. Additionally, males tend to spawn earlier and longer, thus releasing much more spleen into the water than desired.
Recondition the animals after the spawning induction activity. Animals that have spawned successfully are placed in a separate broodstock recovery
Egg collection and monitoring
Immediately collect and rinse the newly-fertilized eggs. Fertilization
Multicellular stage (clumped blastomeres) 3 hours after fertilization, together with some unfertilized and non-viable eggs (empty cells) (right). The zygote is covered with an outer layer called the fertilization membrane, which prevents other sperm from entering the egg. The overall size of the embryo remains the same (150–180 microns), making the dividing cells smaller.
The early gastrula has a characteristic double wall and now begins to grow, taking on a generally oval shape. This will further create an opening (called the blastopore) from the outer wall, which will eventually form the early.
Determine the total number and density of fertilized eggs prior to stocking. After rinsing and placing fertilized eggs into a collection bucket,
Continuous aeration is then provided to ensure that the contents of the bucket are well mixed and evenly suspended. This even suspension is important to achieve a good representation of the samples to be taken for measurement. Egg counting and observation is done using a compound microscope and counting chambers such as the Sedgewick counting chamber.
To estimate the total number of eggs in the bucket, several 1 ml samples (usually taken 5 times) will need to be counted. L = 1,000, constant multiplier to convert density to eggs/liter A = number of eggs from 1st 1-ml sample. Since the total number of eggs and the density in the holding bucket are known, the actual volume is
Incubate the fertilized eggs and embryos in larval rearing tanks. Since the total egg count and density in the holding bucket are known, the actual volume
Hatching
Like other echinoderms, fertilized eggs of sea cucumbers, like those of sandfish, will develop and hatch (out of the eggshell) into what is called the gastrula (250-350 microns in length) of embryonic development. Gentle aeration is provided inside the tank to promote just enough water circulation to keep the gastrula suspended and moving around in the water column. The hatched gastrula will make use of its reserved nutrients and will continue embryogenesis to develop into the early auricularia larvae (350-400 microns in length) that will appear 36-40 hours (or about 2 days) after fertilization.
If enough tanks are available in the hatchery, the gastrula larvae can be transferred to individual larval rearing tanks when they are 2 days old after fertilization. However, for practical purposes, the incubation tank can already serve as the larvae rearing tank without the need to transfer the gastrula, provided proper cleaning and water management are observed (as will be described later).
Larval development
- The auricularia stage
- The doliolaria stage
- The pentactula stage
The lobes also begin to shorten, but the hyaline spheres will now be much larger and closer to the center of the body. Auricularia 2–5 d • The gastrula will grow. and takes about one day to become an early auricularia larva. This stage is compared to the chrysalis or cocoon stage of the caterpillar of a butterfly or moth.
In the nursery, when more than 50% of the larvae have developed into doliolaria, artificial settling plates coated with Spirulina powder are added to the larval tanks. The presence of food in an ideal substrate will encourage larval settlement. Within two to three days after settling, doliolaria larvae will metamorphose into the third major larval stage - the pentactula.
Water management during larval rearing
Clean the tank floor of debris by siphoning. After stocking the
Change water in the larval rearing tanks every 2 days. Seawater inside the larval tanks is changed every 2 days during the auricularia stage (Day 5 to 18)
Feeding management of sandfish larvae
- Feeding schedule for larval sandfish
- Feeding rate calculation
The daily feeding ration can be divided into two parts, namely in the morning (8-9:00 a.m.) and the second part in the afternoon (4-6:00 p.m.). Sandfish larvae begin feeding in the auricularia stage when the larvae are in the pelagic or swimming stage. Practical feeding in the hatchery therefore starts in the afternoon of the first day, but with a smaller amount of 2,500 microalgae cells/.
However, algae cultures can have different densities, so it is important to determine how much volume of the microalgae culture will be required during each feeding period. Therefore, the calculation of feed volumes is dependent on the density of the microalgae stock (eg Chaetoceros calcitrans) in the culture tanks. B = number of cells in the "B" block C = number of cells in the "C" block D = number of cells in the "D" block NB = number of blocks counted.
Settlement plates
All the plates must always be immersed in the water to receive the settling larvae. The spirulina coating on the plates will serve as a settlement signal for the doliolaria larvae. The plates are introduced into the larval rearing tanks when at least 50% of the auricularia larvae have developed into doliolaria larvae.
These can be gently brushed off so they can settle on the plates below instead. Navicula cells will settle evenly on the plates as long as continuous but gentle aeration is provided. Two to three days after settlement, early hatchlings will appear as tiny black dots on the settlement plates.
Water management after settlement
Harvesting of early sandfish juveniles
The juveniles collected in the sieve are large enough to be transported for release in nurseries. These are counted and stored in separate containers (5-10 liter capacity) at a desired density depending on the nursery system they are transported to. These smaller juveniles are placed in pre-prepared larval rearing tanks with plates and fed continuously with Navicula slurry for a few days or weeks to reach harvest size.
A desired number of juveniles are temporarily stored in individual baskets or basins of Navicula sludge prior to packaging.
Packing and transport
Poor water quality
Limited microalgae supply
Examples of commercial microalgae concentrates that can be imported (left) or locally produced such as those from SEAFDEC/AQD (right). Culture tanks should be exposed to diffused sunlight (through a semi-opaque roof covering) to promote algae growth. The initial stock of Navicula in a 10 liter carboy (see section 3.2) can be grown in a 1 ton tank with clean seawater (filtered and UV treated) and plates.
After about four days of culture, Navicula cells will have settled on the plates and can then be harvested. It can be placed in the larval rearing tanks to induce the establishment of doliolaria larvae. However, using the Navicula plates will require many algae culture tanks and will take several days before they are ready for use.
Bloodworms
Copepod infestation
This insecticide can be effective in removing the adult swimming cephalopod, but the smaller nauplii, especially the eggs, may still remain viable. At the SEAFDEC/AQD hatchery, we do not recommend and use such chemicals, especially since the practical flushing procedures described above can have a similar level of effectiveness. This can be avoided by proper cleaning and disinfection procedures described in earlier sections of this manual.
Unstable water temperature
Selected References
The role of the hyaline bulbs in sea cucumber metamorphosis: lipid storage via transport cells in the blastocoel. Seed production from sea cucumber farms in Malaysia: from research and development to pilot scale production of the sandfish Holothuria scabra. We acknowledge the Australian Center for International Agricultural Research (ACIAR: FIS/2007/117) and the Japan International Research Center for Agricultural Sciences (JIRCAS) for providing financial support for the construction of the sea cucumber hatchery in 2010.
We also acknowledge JIRCAS for the additional funds in improving the hatchery's facilities in 2014. We are grateful to the current and past managements, officers and staff of all four divisions of SEAFDEC/AQD for supporting the functions, maintenance, and activities of the sea cucumber hatchery. Rodriguez has been the hatchery manager of the SEAFDEC/AQD Sea Cucumber Hatchery since its construction in 2010.
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