Method for producing artificial seeds of Rapana venosa

Abstract

The present invention provides a method for producing artificial seeds of whelks that enables year-round production by hatching larvae from egg masses obtained through spawning and implementing appropriate management according to larval development stages, thereby reducing mortality rates and increasing production yields. By managing hatched larvae according to early, middle, and late stages, it is possible to reduce mass mortality occurring during the artificial seed production process. Furthermore, by analyzing the correlation between the installation of chillers and the replacement cycle of housing filters for water quality control and water purification efficiency, it is possible to prevent the influx of external pathogens (ciliates, scuuchica) caused by rapid environmental changes during periods of high water temperature. Additionally, by artificially inducing larval settlement, the metamorphosis period can be shortened and growth variations between individuals can be reduced. Moreover, it is possible to establish a complete whelk aquaculture system that progresses from seed production to intermediate rearing to main rearing.

Description

Technology Field

[0001] The present invention relates to the horned snail ( Rapana venosa The invention relates to a method for producing artificial seeds, and to a tank for rearing whelks and a method for producing artificial seeds that can reduce mortality and increase production by hatching egg mass larvae obtained by spawning from broodstock and implementing appropriate management at each stage of larval development. Background Technology

[0002] Recently, due to heavy rainfall caused by climate change, fisheries damages such as low specific gravity in coastal waters and mass mortality of farmed organisms caused by high water temperatures are increasing. Therefore, there is a need to develop aquaculture technology for the otothermal and otohal periwinkle, which possesses optic-thermal and optic-halo characteristics, in order to discover new high-income aquaculture species. The periwinkle exhibits excellent survival capabilities even in environments of rapid low salinity caused by frequent coastal high water temperatures and heavy rainfall.

[0003] Spiked whelk ( Rapana venosa It is a species belonging to the order Neogastropoda and the family Muricidae, distributed along the west and south coasts of Korea, and inhabits sandy, sandy-mud, sandy-gravel bottoms or rocks at depths of around 10m. It is a large carnivorous snail with a shell typically around 12cm in size.

[0004] Due to its good taste, it is used in various ways, such as eating it or making porridge, and its price is relatively high. An analysis of domestic production and unit price trends for sea snails revealed that production volume decreased by 841 tons from 7,365 tons in 2021 to 6,524 tons in 2025, while the production price per kg rose slightly by 449 won from 5,221 won in 2021 to 5,870 won in 2025. As such, expectations are rising for the whelk as a new source of income for coastal fishermen.

[0005] However, current production of the whelk largely relies on natural harvesting, and systematic artificial seed production and aquaculture technologies remain in their early stages, resulting in significant resource variability and difficulty in ensuring a stable supply. Furthermore, since whelks have an ecological characteristic of preying on bivalves such as Manila clams and oysters, indiscriminate fluctuations in their population can have direct or indirect impacts on the coastal shellfish aquaculture industry; therefore, planned and scientific aquaculture techniques that consider these ecological characteristics are necessary.

[0006] Figure 1 shows the developmental process of a typical whelk. The whelk has high reproductive potential as a single female lays an egg mass consisting of about 100 egg sacs 3 to 4 times a year. However, during the metamorphosis and settlement phases (between 10 and 15 days after hatching) when they transition to a benthic life, they rapidly consume physiological energy, so if food supply or environmental management is not provided, the survival rate drops sharply and can lead to mass mortality.

[0007] Accordingly, the present invention aims to provide a method for producing artificial seeds of the whelk that enables mass production of spat by considering the ecological characteristics of the whelk, establishing a technology for inducing the settlement of metamorphosed larvae to advance the larval rearing system and improve the settlement rate, and improving the survival rate. Prior art literature

[0008] Korean Registered Patent No. 10-1849089 Artificial Seedling Aquaculture Device for Intermediate Rearing of Shellfish Korean Registered Patent No. 10-1011174 Equipment and Method for Aquaculture of Freshwater Snails Korean Registered Patent No. 10-2856889 Nbs-based Habitat Model for Jujube Ear-shaped Goby and White-footed Fiddler Crab The problem to be solved

[0009] The present invention aims to provide a method for producing artificial seeds of the whelk that enables year-round production by utilizing the whelk, an existing bivalve predator, to connect to a high-value aquaculture industry. means of solving the problem

[0010] A method for producing artificial seeds of the whelk capable of year-round production according to one embodiment of the present invention comprises: a broodstock maturation and spawning stage (a) in which broodstock are collected, heated and reared at 23.0 ± 0.5 ℃ with a salinity of 20 psu or higher, and fed every other day with 3~5% of body weight using ark clams or shellfish as feed, and then mated and spawned; an initial larval management stage (b) in which microalgae are supplied as feed to the initial veliger larvae hatched from the egg mass spawned in stage (a) around 1~3 days after hatching, and then introduced into a downwelling tank; a mid-stage larval management stage (c) in which a downwelling system is applied to the mid-stage larvae that have grown to a shell height of 400㎛ or more through stage (b); and a metamorphosis and settling stage (d) in which a settling substrate is installed inside the tank to induce metamorphosis in the settling larvae that have grown to a shell height of 800㎛ or more through stage (c).

[0011] The above-mentioned downwelling tank may be configured such that a cage formed as a circular frame structure of a certain diameter and length is installed at a certain distance from the bottom of the tank, a larval net with a mesh size to prevent larval loss is installed at the bottom of the cage, larvae are introduced into the cage, a water supply unit is provided facing the inside of the cage so that water flows from top to bottom within the cage to form a downwelling system, and an aeration device is installed on the bottom of the tank.

[0012] In the above step (d), microalgae and clams or live feed may be supplied in parallel.

[0013] The above microalgae Isochrysis sp. , Tetraselmis sp. , Chaetoceros It may be one or more selected species among sp. The substrate of step (d) above may be a scallop cage net filled with a mixture of onion nets and shellfish nets.

[0014] When supplying the above microalgae feed, after microscopically examining the feed concentration in the rearing water using a hemacytometer, 100 ~ 300 × 10 per larval density 4 Feeding may be performed twice a day to maintain a constant cell / mL concentration. Effects of the invention

[0015] The present invention manages hatched larvae according to the early, middle, and late stages to reduce mass mortality occurring during the artificial seed production process. By analyzing the correlation between the installation of chillers, the replacement cycle of housing filters, and water purification efficiency for water quality control, it is possible to prevent the influx of external pathogens (ciliates, scuuchica) caused by rapid environmental changes during periods of high water temperature. Furthermore, by artificially inducing larval settlement, the metamorphosis period can be shortened and growth variations between individuals can be reduced. Additionally, it is possible to establish a complete aquaculture system for whelks that progresses from seed production to intermediate rearing to main rearing. Brief explanation of the drawing

[0016] Figure 1 shows the developmental process of a typical whelk. Figure 2 shows a schematic diagram of the method for producing artificial seeds of the whelk that can be produced year-round according to the present invention. Figure 3 shows the color change of the egg sac according to maturation in Experimental Example 1. Figure 4 shows the substrate according to Experimental Example 2. Figure 5 shows a downwelling system according to Experimental Example 2. Figure 6 shows the mature egg sac of the whelk and the larval growth process by age according to Experimental Example 2. Figure 7 shows the growth process of benthic spat of the whelk according to Experimental Example 2 by age. Figure 8 shows the culture and feeding stages of the feed organisms. Figure 9 shows the average water quality environment during the 1st to 5th trials according to the experimental examples of the present invention. Figure 10 shows the rearing environment monitoring and stage measurement according to Experimental Example 4. Specific details for implementing the invention

[0017] Hereinafter, the method for producing artificial seeds of the whelk capable of year-round production according to the present invention will be described in detail with reference to the drawings.

[0018] FIG. 2 shows a schematic diagram of the method for producing artificial seeds of the whelk capable of year-round production according to the present invention. The method comprises: a broodstock maturation and spawning stage (a) in which broodstock are collected, reared under heating at 23.0 ± 0.5 ℃ with a salinity of 20 psu or higher, and managed by feeding ark clams or shellfish as feed at a rate of 3–5% of the broodstock's body weight every other day, followed by mating and spawning; an early larval management stage (b) in which microalgae are supplied as feed to early veliger larvae hatched from egg masses spawned in stage (a) around 1–3 days after hatching, and the larvae are introduced into a downwelling tank; and a mid-stage larval management stage (c) in which a downwelling system is applied to mid-stage larvae that have matured to a shell height of 400 µm or more through stage (b). It may consist of a metamorphosis and settling stage (d) in which a settling substrate is installed inside a tank to induce metamorphosis in a settling larva that has grown to a height of 800㎛ or more through the above (c) stage.

[0019] The downwelling tank referred to in the present invention may be configured such that a cage formed as a circular frame structure of a certain diameter and length is installed at a certain distance from the bottom of the tank, a larval net with a mesh size to prevent larval loss is installed at the bottom of the cage, larvae are introduced into the cage, a rearing water supply unit is provided toward the inside of the cage so that rearing water flows from top to bottom within the cage to form a downwelling system, and an aeration device is installed on the bottom of the tank.

[0020] The above-mentioned rearing tank may be implemented as a tank structure typically installed in an aquaculture farm, and may be structured to allow for the supply, drainage, and sludge discharge of rearing water.

[0021] The substrate of step (d) above may be a scallop cage net filled with a mixture of onion nets and clam nets. The scallop cage net referred to above is a commonly known type, formed by circular plates with multiple perforations spaced apart at regular intervals vertically to form layers, and a cage net section surrounding the circular plates. It is preferable that the mesh size of the cage net be 3-5 cm based on the spread size. The interior of the cage net is filled with a mixture of onion nets and clam nets. The onion net may be a commonly known type formed with a mesh size of 1-5 mm. The clam net may be a commonly known type formed with a mesh size of 1-3 cm.

[0022] The present invention manages hatched larvae according to the early, middle, and late stages to reduce mass mortality occurring during the artificial seed production process, and analyzes the correlation between the installation of a cooler and the replacement cycle of a housing filter and the water purification efficiency to control the water quality environment, thereby preventing the influx of external pathogens (ciliates, scuuchica) caused by rapid environmental changes during high-temperature periods, and artificially induces the settlement of larvae to shorten the metamorphosis period and reduce growth variations between individuals, as well as promoting the establishment of a complete aquaculture system for whelks that leads from seed production → intermediate rearing → main rearing.

[0023] The present invention is for overcoming mass mortality occurring around 10 days after hatching. Isochrysis sp. , Tetraselmis sp. , Chaetoceros In order to establish a mixed feeding system for each larval stage of microalgae such as sp. and to develop bottom-inducing technology, we utilized a downwelling system and bottom-inducing substrates to identify stage-specific rearing environment conditions that allow planktonic larvae to smoothly transition to benthic life through the following experiments.

[0024] <Experimental Example 1> Broodstock Stocking and Maturity Management

[0025] 1-1. Experimental Method

[0026] The whelk used in Experimental Example 1 ( Rapana venosa ) The broodstock were collected from individuals weighing 150g or more (570 individuals, 88kg) caught in the coastal waters near Goheung and Yeosu from April to June 2025, and the collected broodstock were each placed in 4-ton circular tanks at the Namhae Specialty Products Experiment Station and underwent a stabilization period.

[0027] At the time of stocking the broodstock, from April to June, the average water temperature in the waters near the Namhae Specialty Products Experiment Station (Sinchon-ri, Geumsan-myeon, Goheung-gun) was 13.8 to 21.1 ℃, which was lower than the 22 to 24 ℃ required for maturation and spawning. Therefore, to secure fertilized eggs earlier than the natural spawning season, heating management was implemented to maintain the rearing water temperature at a constant 23.0 ± 0.5 ℃. An automatic temperature control system was operated to prevent rapid changes in the rearing water temperature and to promote the metabolic activity of the broodstock to accelerate maturation.

[0028] In an environmental tolerance experiment of adult whelks conducted in 2024, it was confirmed that 92% of the individuals survived for 22 days at a water temperature of 32 ℃. Although there were no significant results in the salinity range of 15 to 25 psu, all individuals died within 10 days of the start of the experiment in the 10 psu range. Based on the results, it was found that salinity concentrations above 20 psu did not affect the survival rate.

[0029] Nutritional management involved supplying fresh shellfish, such as Manila clams and short-necked cockles, every other day at a rate of approximately 3 to 5 percent of body weight to induce sexual maturation and the production of high-quality egg sacs in the mother.

[0030] 1-2. Experimental Results

[0031] The first spawning was observed approximately 20 to 25 days after mating, which is consistent with the typical spawning preparation period (17 to 30 days) after mating. The common whelk is a summer spawning species, and the results from the mating period of this study (May to August) were similar to those of previous studies covering the mating cycle from May to the end of August, and spawning usually began around 15 to 30 days after mating.

[0032] Spawning occurs up to 3 to 4 times at an average interval of 1 to 3 days and concludes within 10 months of starting, with the released egg masses attached to shells or surrounding terrain. At this time, the diameter of the fertilized eggs is approximately 150 to 275 µm, and the development period to the larval stage was found to be around 20 days at a water temperature of 25°C. During this period, the larvae are known to consume albumin, a type of protein contained in the egg sac.

[0033] Figure 3 shows the color change of egg sacs according to maturation in Experimental Example 1. The color of the egg sacs changed from bright yellow initially to light brown to dark brown as the embryo developed, and finally to light black, while dead egg sacs showed purple. The egg masses obtained at the beginning of the experiment had large egg diameters and showed a high hatching rate.

[0034] According to this experimental example, by promoting maturation of the mother broodstock and establishing early egg collection technology through heating management at around 24°C, the seed production period was extended and high-quality fertilized eggs were continuously supplied, allowing seed production to be carried out a total of 5 times.

[0035] After July, miniaturization of egg masses and deterioration of egg quality were observed due to the depletion of internal nutrients in the broodstock and accelerated metabolism caused by the cumulative increase in temperature, which is consistent with research results that the spawning cycle of the whelk is closely related to the nutritional status of the broodstock and changes in water temperature.

[0036] Therefore, in order to maintain a consistent pattern of artificial seed production and to produce stably throughout the year, it is judged that a method of relying solely on the natural spawning season should be abandoned. Instead, when the water temperature is low, maturation should be promoted through heated rearing to advance the spawning season by 1 to 2 months, and during periods of high water temperature, maturation inhibition technology through cooling to prevent the degeneration of germ cells should be combined.

[0037] <Experimental Example 2> Larval Rearing System and Settling Substrate

[0038] 2-1 Experimental Method

[0039] To ensure the technical completeness of artificial seed production for whelks and to standardize the optimal rearing process for each developmental stage, a total of five artificial seed production experiments were conducted from May to October 2025. Each experiment focused on finely adjusting rearing environmental conditions to reduce larval metamorphosis and mortality rates during the settling stage by progressively improving rearing methods based on the results of the previous experiment. Table 1 below shows the experimental conditions according to the rearing system and settling substrate for each stage, and Table 2 shows the settling substrate conditions according to Experiment Example 2.

[0040] Experimental conditions according to rearing systems and substrates by order Order Egg collection and hatching period Hatching amount Main breeding system note 1st 5. 28. ~ 6. 8. 1.2 million General tank rearing Settlement substrate test 2nd 6. 19. ~ 7. 2. 1.6 million Downwelling Bottom landing induction test 3rd 7. 2. ~ 7. 14. 2 million animals Downwelling + Netting temperament Securing maximum ground clearance 4th 7. 22. ~ 7. 31. 1 million General tank rearing High-temperature survival monitoring 5th 8. 21. ~ 10. 14. 1.2 million Downwelling + Long-term rearing Monitoring of 120,000 bottom-dwelling spat

[0041] Rearing device and bottom substrate conditions Device name Main specifications Internal configuration and features Main Uses and Advantages square cage tank 100×100×80 cm Multiple diatom plates arranged vertically Induction of mass settlement of larvae and provision of initial growth space Scallop net Diameter 50, height 150cm Internal onion net and clam net mixed filling Maximizing the surface area of ​​the substrate and dispersing rearing density through a multi-tiered structure Downwelling tank Diameter 50, height 60cm Attach 300~400㎛ mesh to the bottom, install thermal cover Prevention of larval sinking and reduction of mortality rate through the formation of downward water currents Onion net / Clam net Mesh size 3 ~ 15 mm Net-shaped synthetic resin mesh Stimulation of physical grounding instincts and provision of shelter for metamorphosed larvae

[0042] In the first artificial seed production, the basic physiological characteristics of hatched larvae and the initial survival rate according to rearing density were investigated, and the growth rate and development process of the larvae were monitored by applying a rearing method using bottom substrates such as onion nets and clam nets in existing general circular tanks.

[0043] Figure 4 shows the substrate according to Experimental Example 2. In order to overcome the mass mortality during the metamorphosis stage (10 to 13 days old) confirmed in the first experiment, the 2nd and 3rd artificial seed productions were operated in 10 groups using a downwelling circulation system. At the same time, to maximize the settlement efficiency of the larvae, various substrates were mixed and arranged, such as diatom plates in square cage tanks and onion nets and shell nets as substrates inside scallop cage nets, to improve the settlement rate.

[0044] The fourth experiment monitored mortality patterns due to rising water temperature to determine the limits of larval tolerance in high summer temperatures, and the final fifth experiment focused on optimizing the process of the initial intermediate rearing stage after seed production by feeding microalgae and live feed (clams, mussels) in combination within a downwelling system to spat that had successfully settled on the bottom.

[0045] Figure 5 shows a downwelling system according to Experimental Example 2. The downwelling system according to Experimental Example 2 of the present invention can prevent mortality of larvae during the metamorphosis period. First, by increasing the contact area between the microbubbles generated by the aeration installed on the bottom of the downwelling tank and the rearing water, abundant oxygen is continuously supplied into the tank where the larval density is high. Second, mortality caused by the dense concentration of metamorphosis larvae, whose movement slows down, at the bottom of the tank is prevented in advance. Third, by constantly exchanging the rearing water between the downwelling tank and the external tank through aeration, water quality stability is ensured by maintaining a low concentration of waste products, such as ammonia, that may be generated after feeding.

[0046] The downwelling tank, specially designed to reduce larval mortality during metamorphosis, consists of a cylindrical cage with a diameter of 50 cm and a height of 60 cm, and at the bottom of the cage, 300 to 400 are installed according to the larval growth stage to prevent larval loss and ensure smooth rearing water circulation. ㎛ It was attached by applying mesh sizes differentially.

[0047] 2-2. Experimental Results

[0048] According to this experimental example, hatching occurred approximately 10 to 14 days after receiving the egg mass in a water temperature environment of 24 to 25 ℃, and the larvae showed relatively high vitality immediately after hatching.

[0049] During the early larval stage, which is about 1 to 3 days after hatching, vigorous feeding activity of microalgae occurred along with the development of cotton spots, and microalgae were supplied as initial food, and the rearing water was controlled in the downwelling tank so that the larvae would not sink to the bottom of the tank.

[0050] During the mid-period veliger stage, around 4 to 10 days after hatching, rapid growth of the shell occurs and the spiral of the shell begins to form. In this experiment, growth to the 4th to 5th spiral stage (about 600 to 700 μm) was observed.

[0051] At this time, the downward water flow caused by the downwelling tank prevents sinking mortality of larvae and facilitates oxygen supply in the rearing water, and the results of previous studies showing that physical environmental control in larval rearing lowers physiological stress and improves survival rates were confirmed through the growth and mortality of larvae when using a conventional tank and a downwelling tank in the 1st to 5th repeated seed production experiments.

[0052] Generally, during this period, the digestive organs of the larvae develop, leading to a rapid increase in food intake and more active ciliary movement of the cotton moss; therefore, maintaining an appropriate food density is a key factor in determining the success rate of subsequent metamorphosis.

[0053] Figure 6 shows the mature egg sacs of the whelk and the larval growth process by age according to Experimental Example 2. Through monitoring of the amount and frequency of microalgae feeding during the metamorphosis stage in the self-seed production period, the same conclusions as previous research results were drawn regarding the metamorphosis process and growth of the larvae.

[0054] Table 3 below shows the rearing characteristics of artificial seed production and growth stages of the whelk. Around 11 to 14 days after hatching, during the late veliger stage, the shell thickens and the color darkens; it is a time when the larvae show behaviors of attaching to the bottom or walls rather than swimming, and the color of the larvae darkens to brown when viewed with the naked eye.

[0055] Rearing characteristics of artificial seed production and growth stages of whelks Growth stages Key Features and Developments Core breeding technology Incubator Water temperature 24 ~ 25 ℃. Takes 14~20 days after stocking. Color comparison based on egg sac maturation Early (Velizer) Flesh-like development, active microalgae feeding, shell height 200 ~ 500 µm Appropriate feeding during metamorphosis Middle stage (growth stage) Distinct spiral formation, rapid shell height growth, shell height 400 ~ 800 µm Application of downwelling system (prevention of sedimentation mortality) terminal stage (landing stage) Angle height 800 ~ 1,000 µm, degeneration of cotton patches, foot development Timely introduction of substrate (transformation induction)

[0056] As confirmed in the third experiment, during this period of intensive rearing, the animals are vulnerable to parasites such as scuuchica, so the tanks were divided and water quality was thoroughly managed according to growth.

[0057] During the metamorphosis and settling stage around 15 days after hatching, the development of the foot and the degeneration of the cottony membrane were simultaneously observed in settling larvae with a shell height of approximately 800 to 1,000 µm. This result is consistent with research findings on morphological changes and metamorphosis mechanisms according to the growth stages of the whelk, and through self-sproduced seeds, it was confirmed that the timely introduction of an appropriate settling substrate during this period is a critical factor determining the success of the entire artificial seed production process.

[0058] Figure 7 shows the growth process of benthic spat of the whelk according to Experimental Example 2. Due to morphological changes, the swimming organ, the cotton sac, degenerates, and the foot for benthic life develops, causing the larva to start crawling on the substrate. This period can be considered a vulnerable time for the survival of the larva, and experiments have shown that failure to undergo metamorphosis during this process can lead to death.

[0059] In addition, monitoring confirmed that feeding microalgae and live feed (clams, mussels) in combination to early-stage bottom-settled spat resulted in a faster growth rate compared to feeding a single type of microalgae.

[0060] Table 4 below shows the larval settlement efficiency according to the settlement substrate for artificial seed production of whelks according to the present experimental example. In the present experimental example, four different substrates (onion net, clam net, diatom plate, and onion + clam mixed net) were introduced in advance during the metamorphosis period to increase the survival rate of metamorphosis. Regarding the efficiency by settlement substrate, there were more individuals settling in the scallop cage net filled with a mixture of onion net and clam net and the downwelling tank compared to when onion net, clam net, and diatom plate were used as single settlement substrates. It is determined that the main reason for the increase in the settlement rate is that the combination of the dense mesh of the onion net and the three-dimensional spatial structure of the clam net simultaneously provided shelters of various sizes and settlement areas required by the larvae during settlement.

[0061] Larval Settlement Efficiency by Settlement Substrate for Artificial Seed Production of Horned Whelk Settling substrate Injected larvae (ind.) Bottom larvae (ind.) Landing rate (%) Onion net + clam net 3,000 188 6.27 Shell Net 3,000 113 3.77 Shell Net 3,000 75 2.50 Diatom Plate 3,000 52 1.73

[0062] Therefore, for the stable seed production of the whelk, it is considered that diversifying the bottom environment by mixing onion nets and clam nets, rather than using a single substrate, is advantageous for improving productivity.

[0063] Consequently, compared to standard tanks, the rearing method using downwelling tanks showed better data in terms of water exchange efficiency, spat settlement rate, and vigor maintenance when onion and clam nets were used together as substrates; therefore, it is judged that this can be utilized as a standard model for future mass production systems of whelks.

[0064] <Experimental Example 3> Culture and Supply Management of Feed Organisms

[0065] According to Experimental Example 3 of the present invention, considering the physiological characteristics and nutritional requirements according to the developmental stage of floating larvae, three types of microalgae original species with different nutritional values ​​( Isochrysis galbana, Tetraselmis suecica, Chaetoceros calcitrans We obtained ) from our institute's Future Fisheries Research Institute and added concentrated medium to conduct culture for supplying larvae.

[0066] In particular, to supply high concentrations of unsaturated fatty acids (PUFA) essential during the small larval stage Isochrysisgalbana Consisting of as the main food source, and as the larvae grow, high in protein and vitamins Tetraselmis suecica and Chaetoceros calcitrans We aimed to resolve nutritional imbalances that may occur with a single feed supply and to improve metamorphosis and settlement efficiency by feeding them in parallel. Based on the secured original species, mass culture was carried out to secure a sufficient amount of feed necessary for larval rearing, and an appropriate amount of concentrated medium was added according to the concentration to support the optimal growth of microalgae.

[0067] Through this, cell density was increased and the environment was managed to ensure sufficient essential nutrients (vitamins, minerals, etc.) required for the larvae were supplied; sufficient light was applied to enhance photosynthetic efficiency; and continuous aeration using an air stone was performed to prevent sedimentation of the culture medium and facilitate gas exchange.

[0068] In particular, during the high-temperature period (August) when the ambient temperature rises rapidly and cultivation efficiency decreases, a site-specific cooling system was introduced to create a cooling environment using groundwater (17°C) in a large square tank measuring 7×7 m, as there is no in-house feed organism culture room.

[0069] Figure 8 illustrates the culture and feeding stages of the feed organisms. A movable rectangular pool measuring 4 × 2 m was installed inside the tank, and microalgae were introduced. By stably controlling the temperature of the culture medium to below 25 ℃ through heat exchange with groundwater, the death of microalgae due to high temperatures was prevented, and a stable feeding system was maintained during the seed production period.

[0070] During feeding, the feed concentration in the rearing water was inspected microscopically using a hemacytometer every morning, and 100 ~ 300 × 10⁶ per larval density 4 Feeding was carried out twice a day by adjusting the feeding amount to maintain a constant cell / mL concentration.

[0071] In the early larval stage, microalgae were supplied alone, but in the spat stage after metamorphosis, initial micro-feed of crustaceans and live feed such as clam meat and mussel meat were ground in a mixer and fed in combination to promote nutritional balance and growth.

[0072] <Experimental Example 4> Monitoring of Rearing Environment and Measurement of Developmental Stages

[0073] 4-1. Experimental Method

[0074] In order to maintain the stability of the rearing environment, which is directly related to the survival and growth of the larvae according to Experimental Examples 1 to 3 above, water temperature, dissolved oxygen (DO), pH, and salinity (psu) were set as key indicators, and regular measurements were conducted starting at 10:00 AM every day.

[0075] The accuracy of the data was ensured by utilizing a multi-parameter water quality meter (YSI ProSolo) for measurement. In particular, during the high-temperature summer months of July and August, the measurement cycle was increased to twice a day to prevent physiological stress on larvae caused by a rapid rise in water temperature, thereby allowing for an immediate response to environmental changes. Additionally, to prevent physical and chemical contamination of the rearing water, organic matter deposited on the bottom of the rearing tank was removed daily using the siphon principle.

[0076] After cleaning the bottom of the rearing tank, about 40 to 50 percent of the rearing water was exchanged daily using filtered seawater to maintain stable water quality, and the water exchange rate was flexibly adjusted according to the developmental stage of the larvae and the degree of water pollution to maintain an optimal rearing environment.

[0077] To quantify the growth efficiency at each developmental stage of artificial seed production of the whelk, morphological changes in larvae were observed periodically (at intervals of 1 to 2 days) using an optical microscope (OLYMPUS-BX51) and a stereomicroscope (OLYMPUS-SZ61). In addition to simple size measurements, the formation of spirals, the degree of degeneration of the periphery, and the developmental state of the foot were examined. By predicting the transition period from a planktonic to a benthic lifestyle based on these findings, the results were used as a basis for determining the optimal timing for downwelling tank cultivation and substrate input.

[0078] 4-2 Experimental Results

[0079] As a result of analyzing environmental changes in the rearing system for whelk larvae and spat during the test period (May 28, 2025 – October 14, 2025), water quality conditions suitable for whelk habitation were generally maintained stably. The common whelk (average shell height of individuals 32.5 mm, total weight 11.2 g) has extensive ecological tolerance to high temperatures, low salinity, oxygen deficiency, and environmental degradation, and in Korea, it is known to withstand water temperatures between 4 and 27 ℃.

[0080] To ensure the stability of larval rearing, solid suspended matter was removed from the incoming seawater through primary sand filtration, and subsequently, the final rearing water was supplied after undergoing a secondary precision filtration process using a 1.0 μm housing cartridge filter to completely block fine organic matter and external harmful factors. Figure 9 shows the average water quality environment during the 1st to 5th stages according to the experimental example of the present invention.

[0081] ① Water temperature (°C)

[0082] The average water temperature in May and June during the 1st and 2nd seed production periods was stable at 22.9 to 22.9 ℃, but during the 3rd and 4th seed production periods in July and August, which are the high-temperature season, the water temperature rose to 24.7 to 26.4 ℃.

[0083] As the water temperature increased, it had a positive effect of promoting metabolic activity of the larvae and increasing the growth rate, but it was confirmed that it could be a cause of pathogens (ciliaries, scuuchicaids) as confirmed in the 3rd and 4th seed production.

[0084] The average water temperature from August to October during the 5th seed production period was 24.4 ℃, and as the water temperature gradually decreased, larval rearing could be continued for up to 55 days.

[0085] ② Dissolved Oxygen (DO)

[0086] Generally, the whelk is known to be more tolerant to oxygen-deficient environments compared to other shellfish. However, during the larval stage of seed production, it is essential to secure a stable dissolved oxygen level of 5.0 mg / L or higher due to high metabolic activity. In particular, during periods of high water temperature, oxygen solubility decreases and metabolic rate increases simultaneously. Therefore, maintaining the dissolved oxygen saturation at 80% or higher through aeration is considered one of the methods to overcome mass mortality during the seed production period.

[0087] The average dissolved oxygen (DO) during the 1st to 5th seed production periods was highest at 7.20 mg / L in the 1st period (May), when the water temperature was lowest, and lowest at 6.59 mg / L in the 4th test (August), when the water temperature was highest.

[0088] This is a result of the inverse relationship between water temperature and dissolved oxygen, which generally maintained a stable dissolved oxygen concentration of 5.0 mg / L or higher during the seed production period (May to October).

[0089] ③ Salt (psu)

[0090] Generally, the optimal salinity range for whelk larvae is 28–33 psu, and it has been reported that they possess an excellent defense mechanism that inhibits cell expansion through the regulation of amino acid metabolism even in rapidly desalinated environments.

[0091] Table 5 below shows the average water quality environment during the artificial seed production period of the whelk. During the 1st to 5th seed production periods, the salinity concentration was maintained very stably at an average of 32.5 psu (range of 31.2 to 33.8 psu).

[0092] The results of the present invention satisfy the conventionally known optimal range (28 to 33 psu), and it is determined that this stable salt management is a major factor that enabled larvae to focus on growth without unnecessary metabolic energy consumption, thereby leading to 5 cycles of artificial seed production and larval rearing for 55 days.

[0093] Average water quality environment during artificial seed production of whelks division Exam period Water temperature (°C) DO(mg / L) pH Salt (psu) 1st exam 5.23 ~ 6.16 22.92 7.20 7.94 32.78 2nd exam 6.17 ~ 7.11 22.91 6.83 7.99 33.70 3rd exam 7.4 ~ 7.18 24.75 6.82 8.00 33.71 4th exam 7.22 ~ 7.31 26.48 6.59 8.04 33.80 5th exam 8.21 ~ 10.14 24.43 6.66 8.36 33.43

[0094] ④ pH

[0095] It has been reported that when the pH in the rearing water drops below 7.8, the initial shell growth of larvae is inhibited and metabolic stress increases, leading to a significant decrease in the metamorphosis success rate.

[0096] Figure 10 shows the rearing environment monitoring and stage measurements according to Experimental Example 4. During the 1st to 5th seed production cycles, the pH concentration was maintained at an average of 8.1 (range of 7.9 to 8.3), exceeding the risk levels suggested in the literature. In particular, to create a stable slightly alkaline (pH around 8.0) water quality environment during the period when larvae form shells, the accumulation of organic matter, which causes a drop in pH, was prevented in advance by utilizing a filter and a housing cartridge filter, and the pH fluctuation range was minimized through water exchange, thereby enabling the growth of the spat. Industrial applicability

[0097] The present invention has industrial applicability as it is expected to make a decisive contribution to finding a way out of the stagnant abalone farming industry and increasing fishermen's income by establishing a stable artificial seed supply system for whelks, for which consumption demand has recently been increasing, as an alternative item to abalone farming.

Claims

Claim 1 A broodstock maturation and spawning stage (a) in which broodstock are collected, heated and reared at 23.0 ± 0.5 ℃ with a salinity of 20 psu or higher, fed with ark clams or other shellfish at 3–5% of the broodstock's body weight every other day, and then mated and spawned; an initial larval management stage (b) in which microalgae are supplied as food to early veliger larvae hatched from egg masses spawned in stage (a) around 1–3 days after hatching, and then introduced into a downwelling tank; a mid-stage larval management stage (c) in which a downwelling system is applied to mid-stage larvae that have grown to a shell height of 400㎛ or more through stage (b); and a metamorphosis and settling stage (d) in which a settling substrate formed by a scallop cage net filled with a mixture of onion nets and clam nets is installed inside the tank to induce metamorphosis in settling larvae that have grown to a shell height of 800㎛ or more through stage (c). Artificial seed production method Claim 2 In claim 1, the downwelling tank is characterized by having a cage formed as a circular frame structure of a certain diameter and length installed at a certain distance from the bottom of the tank, a larval net with a mesh size to prevent larval loss installed at the bottom of the cage, larvae introduced into the cage, a water supply unit provided toward the inside of the cage so that water flows from top to bottom within the cage to form a downwelling system, and an aeration device installed at the bottom of the tank. Rapana venosa Artificial seed production method Claim 3 In paragraph 1, in step (d) above, microalgae and clams or live feed are supplied in parallel, and the microalgae are Isochrysis sp. , Tetraselmis sp. , Chaetoceros A whelk characterized by being one or more selected species from sp. Rapana venosa Artificial seed production method Claim 4 In paragraph 1, the microalgae feed is supplied by examining the feed concentration in the rearing water using a hemacytometer, at a rate of 100 to 300 × 10 per larval density. 4 A method for producing artificial seeds of *Rapana venosa* characterized by feeding twice a day to maintain a constant cell / mL concentration Claim 5 delete

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