A Complete Analysis of the Key Technical Points for Artificial Jellyfish (Rhopilema esculentum) Farming
In China, the jellyfish fishery has a long history, with the highest annual yield reaching 58,000 tons. However, for reasons that are still not fully understood, its resource volume fluctuates greatly from year to year; sometimes there is so much that there is no time to process it and it is left lying on the beach, while other times it vanishes without a trace.
Artificial farming techniques for jellyfish
Pond selection
Choose a pond relatively close to the sea with convenient water intake and drainage (ideally one that can exchange water even during neap tides).
It is best if there is a freshwater source near the pond so that the water salinity can be adjusted.
The pond should preferably be more than 20 mu in size, and the bigger the better.
The water depth should be more than 1 m, with 1.5-3 m being most suitable.
The slope of the bank should be as steep as possible. If the slope is too gentle, a fence net or plastic sheeting should be added at a water depth of 0.5 m along the bank to prevent jellyfish from stranding and dying, so pay attention to this.
Pond water intake and drainage
The water inlet should be fitted with a fence net to prevent the entry of harmful organisms such as miscellaneous fish and shrimp. The mesh size of the fence net should be around 40-60 mesh. The pond's drainage outlet should also be fitted with a fence net, and the mesh size should be the same as that of the inlet to prevent fry from escaping during drainage. The area of the fence net should be relatively large, depending on the specific size of the pond. The mesh size can gradually be increased as the jellyfish grow. During drainage, the water flow should be as gentle as possible to prevent jellyfish fry from sticking to the drainage net and dying.
Seedlings should only be released 10 days after filling with water. After filling, the water can be fertilized appropriately according to conditions to ensure a certain amount of zooplankton.
Preparations before releasing seedlings
Test the water quality, mainly water temperature, salinity, pH value, etc. This work should be done by technical personnel, and you can seek help from the seedling breeding facility. It must be accurate, as this affects the survival rate after seedling release.
Inform the seedling breeding facility of the pond's water temperature and salinity before releasing seedlings, and only then can it be determined whether seedlings can be released based on the size of the difference between indoor and outdoor pond water quality conditions. The suitable water temperature range for jellyfish farming is 15-35°C, with 22-28°C being optimal; the suitable salinity range is 8‰-36‰, with 18‰-30‰ being optimal.
For ponds with banks that are too gently sloped, a fence net or plastic sheeting should be added at a water depth of 0.5 m along the bank before releasing seedlings.
Releasing seedlings
The time for releasing seedlings should be chosen on a morning or evening with good weather, preferably windless and without direct sunlight.
The density of seedling release should be strictly controlled below 300 individuals/mu. Excessive density can cause oxygen deficiency, slow growth, and failure to grow large. The specific release density should be linked to the pond size, water depth, water quality conditions, and water exchange conditions. If conditions are good, the density can be higher; if conditions are poor, definitely do not release too many, otherwise farming may fail.
During transport, jellyfish seedlings should be oxygenated, shielded from light, and packed with ice to prevent temperature rise.
When releasing, pour the seedlings into a relatively large container, add some pond water, and let them acclimate for a period (10-20 minutes) before putting them into the pond.
It is best to transport the seedlings directly to the middle of the pond and sprinkle them evenly and slowly into the pond. Do not rush the operation, to prevent injuring the seedlings.
Farming management
Jellyfish farming basically adopts a no-feeding method, so water exchange (replenishing natural food in the water body) is very important for jellyfish farming.
After releasing seedlings, if the weather is normal and water quality conditions are normal, no water exchange is needed for 7 days. After 7 days, a small amount of water can be exchanged (no more than 20% each time).
In the early stage of jellyfish farming (10-20 days), ponds with good water exchange conditions can exchange water daily, and the principle of exchanging small amounts frequently should be followed. It is best not to carry out large-scale intake and drainage, as that can harm the seedlings (such as seedlings sticking to the net and dying), especially before the jellyfish bell diameter grows to 5 cm.
In bad weather such as strong wind or heavy rain, it is best not to exchange water, so as to avoid too great an environmental change that would adversely affect jellyfish growth.
Before exchanging water, measure the temperature and salinity of the new water to be used; the difference from that in the pond must not be too great. The salinity change range must not exceed 10‰; if it exceeds this amount, water cannot be exchanged.
The salinity of the pond water should preferably be maintained between 20‰ and 30‰. For ponds with freshwater resources nearby, freshwater should be fully utilized to adjust the pond water salinity. Within the suitable range, maintaining relatively lower salinity is very beneficial to jellyfish growth. However, freshwater must be added evenly, and jellyfish must not die because of locally excessively low salinity.
Observe jellyfish activity and growth at all times, and monitor water quality changes and the amount of zooplankton in the water.
The amount of food organisms.
In the early stage of pond farming of jellyfish, plankton in the pond is abundant, but by the late stage of farming, the amount of plankton in the pond can no longer meet growth needs, and at this time water should be fertilized. Three main methods are used for fertilizing: first, hanging bags of chicken manure to fertilize, using 10 kg of fermented chicken manure per bag, hanging 150 bags/sq m. When water transparency reaches 40 cm, immediately remove the chicken manure bags to avoid the pond water becoming too fertile; second, fertilizing with nitrogen fertilizer, applying nitrogen fertilizer into the water at a ratio of 22.5 kg/hm2; third, fertilizing with phosphate fertilizer, applying phosphate fertilizer into the water at a ratio of 30 kg/hm2. In addition, natural rotifers, brine shrimp, or cladocerans, etc., can also be artificially introduced for live feeding. When jellyfish farming density is relatively high, ground fish paste can also be fed to provide food for the jellyfish. But this method must involve following the jellyfish around the pond to feed them, and adhering to the principle of "feed little but often."
Water quality management.
When farming jellyfish in ponds, in order to maintain pond water quality, the water body must be exchanged frequently. Through water exchange, not only is sufficient food organisms provided for jellyfish growth, but the water body can also be kept fertile, lively, tender, and fresh, which stimulates and promotes jellyfish growth. Water exchange must adhere to exchanging small amounts frequently and avoid large-scale drainage and filling. Seaweed in the pond is also very important for maintaining water quality, and seaweed in the farming pond should be regularly removed. Research shows that by artificially inoculating Chlorella to cultivate a dominant population in the pond, the pond environment can be improved, natural food for jellyfish can be cultivated, and farming costs can be reduced.
Maintaining the balance of physical and chemical factors in the water body.
Research has found that when jellyfish sink to the bottom and die, the dissolved oxygen is less than 3 mg/L and the ammonia nitrogen value is greater than 374.45 Lg/L; this value can be considered the threshold causing jellyfish death. Only when the water temperature is 18-28°C, salinity 18-28, pH 7.5-8.5, and dissolved oxygen \1.5 mg/L are jellyfish active, their food intake increases, and they grow rapidly. Therefore, attention should be paid to regulating the physical and chemical factors of the water body within an appropriate range. When the water temperature difference does not exceed 3°C, the pH value is stable at 7.5-8.5, and the ammonia nitrogen value is less than 0.2 mg/L, seedlings can be released.
Primary productivity of the water body.
Research has found that during jellyfish farming, the primary productivity of the water body is not only mainly affected by seawater transparency, but also by factors such as light, salinity, and nutrients. According to the proportional relationship between transparency and primary productivity, within a certain range, freshwater should be added to increase water transparency. Transparency is generally controlled at 30-50 cm to ensure sufficient primary productivity and promote rapid jellyfish growth.
Seedling cultivation
Preparations
The seedling pond is used to keep brood jellyfish and cultivate larvae. Any large container can be used, but a smooth cement pond is best.
The attachment substrate is used for polyp attachment. Any hard, non-toxic material can be used; for large-scale production, corrugated boards are best.
For other matters, it is best to have a dedicated cement pond for hatching brine shrimp. There are no special requirements for heating and intake/drainage systems; ordinary production environments can meet the requirements.
Sources of brood jellyfish
There are two sources of brood jellyfish: one is the fully artificially cultivated type, mainly suitable for areas where it is very difficult to collect brood jellyfish from natural sea areas, such as the coastal areas of Zhejiang. The other is naturally collected sexually mature brood jellyfish, which can be divided according to collection location into two types: collection from natural sea areas and capture in artificially stocked shrimp ponds. Relative to brood jellyfish quality, whether in terms of egg-carrying capacity or individual size, the latter is better than the former. Moreover, judging from the farming situation in the past two years, jellyfish collected from farming ponds have shown serious degeneration due to kinship among brood jellyfish, manifesting as uneven individual sizes, with small jellyfish being the majority.
Spawning and hatching
At natural water temperatures during the peak breeding period, unfertilized eggs disintegrate after 3-5 hours; fertilized eggs begin cleavage after a period of time, then develop into early planula larvae.
Artificial hatching procedure
Water storage and water treatment: Before the brood jellyfish enter the pond, scrub the pond clean and fill it with new seawater as the hatching pond. Add EDTA (disodium ethylenediaminetetraacetate) to the seawater to chelate heavy metal ions, which helps improve the hatching rate.
Sex ratio pairing: A female-to-male ratio of 2:1 is best. An appropriate brood jellyfish density is conducive to mutual induction of gamete release between male and female individuals.
Sampling and microscopic examination: After introducing the brood jellyfish, samples should be continuously taken from the bottom of the pond and observed under a microscope to see whether spawning has occurred and whether cleavage has appeared. After that, sample and observe once at intervals until a large number of dividing eggs are found or unfertilized eggs are no longer fertilized.
After all hatching embryos have become planula larvae, quantify them using the volumetric method. Under normal circumstances, the hatching rate is above 90%.
Metamorphosis, attachment, and management of planula larvae
Planula larvae rotate counterclockwise and after a period metamorphose into polyps. The front end attaches to form the foot and stalk, and the rear end forms the mouth and tentacles. If no attachment substrate is encountered during metamorphosis, they metamorphose in a floating state, with the stalk pointing upward and hanging upside down at the water surface. The end of the stalk has adhesive cells and attaches easily when it contacts an attachment substrate. After planula larvae metamorphose into polyps, the vast majority attach to the underside of corrugated boards. After polyp attachment, fresh seawater should be added in a timely manner.
After the larval cultivation pond is filled with water, the following four management measures are generally adopted: First, control light to prevent miscellaneous algae and the like from multiplying on the seedling attachment devices, so as to increase the survival rate of polyp larvae; second, maintain temperature. After the water temperature in the pond drops below 10°C in late autumn, indoor warming facilities should be provided to maintain the pond water temperature at 5-10°C. In spring, when the indoor water temperature rises to a suitable temperature, polyp larvae begin strobilation and subsequently release ephyra larvae; third, feed in a timely manner, using rotifers, copepod nauplii, brine shrimp nauplii, etc. as food. The feeding frequency depends on water temperature and feeding conditions, and generally once a day is sufficient. After polyp larvae are satiated they appear light yellow, and when hungry they appear pale white. Therefore, feeding frequency and feeding amount can be increased or decreased as appropriate according to the depth of polyp body color, mainly based on microscopic examination; fourth, exchange water in a timely manner. Polyp larvae are small, move little, have low oxygen consumption, and produce relatively little metabolic waste. Below 20°C, the water temperature is low and metabolism is slow, so there is no need to exchange water frequently. When exchanging water, use the siphon method to draw out seawater with sediment from the bottom of the pond, then add an equal amount of fresh seawater.
A stolon grows from the side of the polyp body, and its end attaches to form a new foothold. The end of the original stalk gradually separates from the attachment point. The process of forming podocysts can proceed continuously, and generally an individual can form one to more than a dozen podocysts. After podocysts form, under suitable conditions, new polyps can sprout from their top. During and after the growth of new polyps, they can likewise form new podocysts and sprout a generation of polyp larvae.
Cultivation of ephyra larvae
When the temperature rises to a suitable temperature the following year, polyps begin to show strobilating individuals. The number is closely related to the size of the polyp, generally about 1 to 7. Newly born ephyrae are colorless and translucent, with a diameter of 2-4 mm. After 7-10 days of growth, the bell diameter reaches 10 mm, and they are mid-stage ephyrae or young jellyfish. After 15-20 days of growth, the bell diameter reaches about 20 mm, and they become juvenile jellyfish.
The following points should be noted in ephyra cultivation:
Feed regularly and in fixed amounts: After ephyrae are satiated, they generally need 3-4 hours to digest the food, so they are generally fed once every 4 hours, with slight adjustments based on visual observation and microscopic examination.
Water exchange: During the ephyra cultivation stage, the temperature is high, food intake is large, and the metabolic waste and residual bait produced easily spoil the water quality. This requires us to exchange water in a timely manner. In the early stage of ephyra cultivation, the water exchange amount is half the volume daily, completed in two sessions. In the middle and late stages, exchange the full volume (when water quality is poor, the entire pond volume can be exchanged twice a day). When exchanging the full pond volume once, the pond water must not be drained all at once, but should be completed in three to four sessions.
Aeration: The radial marginal lobes and canal system of newly born ephyrae have not yet developed, their floating ability is very weak, and the vast majority of individuals settle to the bottom of the pond. Generally, slight aeration is used to drive their floating, feeding, and growth. Under artificially controlled conditions, the survival rate from ephyra larvae to the young jellyfish stage can generally reach above 90%. The survival rate to the juvenile jellyfish stage can reach above 85%.
Sale
When juvenile jellyfish grow to more than 2 cm, they have reached the saleable size and should be quantified by the volumetric method before sale.
We used shrimp farming ponds to conduct a three-dimensional ecological farming experiment for jellyfish, adopting methods such as inoculating fertilized water to directionally cultivate basic food and using photosynthetic bacteria to improve water quality, thereby optimizing the farming environment. At the same time, multi-species mixed farming was carried out, which both fully utilized the water body and improved comprehensive farming benefits.
Materials and methods
① Pond selection: Use a 500-mu pond, with an average water depth of more than 2 m. Intake and drainage are unobstructed, and there are blocking net facilities around the pond.
② Disinfection: Disinfect with 200 kg/667 sq m of quicklime to kill harmful organisms and pathogens.
③ Water intake: Fill with 30 cm of water through an 80-mesh sieve silk net, and disinfect with bleaching powder containing 32% chlorine at 30×10⁻⁶.
④ Releasing seedlings: Release seedlings with a bell diameter of more than 1.5 cm. Use a combination of a seedling breeding room and earthen ponds for temporary rearing. During the temporary rearing period, feed high-quality Artemia nauplii, rotifers, cladocerans, etc.
⑤ Jellyfish harvest: For the first crop, when the commercial size of the jellyfish reaches about 3 kg each, catch them with a large buckle net; for the second crop, according to market conditions, they can be raised to 4-5 kg each before being sold; for the third crop, the jellyfish can be sold early, so that shellfish harvest will not be affected.