Method for conveniently and noninvasively recovering parents from net cage after large-scale artificial breeding of ricefield eels

Abstract

The invention discloses a method for conveniently and noninvasively recovering parents from a net cage after large-scale artificial breeding of ricefield eels, which comprises the following steps of: deepening pond water in a breeding soil pond to force the ricefield eels to get out of soil, and putting a net tool soaked in the pond water into the center of the net cage in the breeding soil pond, a small gauze package containing earthworms is placed in the center of the upper portion of the top of each net, and the finless eels are trapped into the nets; starting to harvest ricefield eel parents in the morning of the next day, lifting the netting gear from each net cage one by one, enabling one corner of the bottom of the netting gear to be the lowest and to be aligned with the opening of the plastic box for recovering the parents, enabling the trapped ricefield eel parents to slide to the corner, pushing aside the opening near the ricefield eel by hands, enabling the ricefield eel to slide into the plastic box from the opening, and counting; according to the method, the nylon net which suspends in water and is provided with the earthworm bait is used for trapping the ricefield eels into the net, so that the purpose that parents are conveniently and efficiently recaptured and bred and are not injured is achieved, and the parent recapturing rate of the method can reach 95% or above.

Description

Technical Field

[0001] The invention belongs to the technical field of aquaculture, and particularly relates to a method for conveniently and non-invasively recovering parents of yellow eels from a net cage after large-scale artificial propagation. Background Art

[0002] In recent years, the natural habitat of the eel has become increasingly polluted due to the use of pesticides and chemical fertilizers. This depletion of resources has driven up market prices, exacerbating overfishing and depleting wild eel seedlings. To meet market demand, artificial breeding is essential. Healthy parent stock cultivation and safe wintering are crucial aspects of artificial breeding. Eels are cold-blooded animals; their food intake decreases when temperatures fall below 15°C, and they begin hibernation at temperatures below 10°C. Common methods for ensuring the safe wintering of eels include dry ponds and water-repellent overwintering. In some areas, overwintering in plastic greenhouses or indoors is also possible. Dry ponds involve draining the pond water, but keeping the soil moist and covering it with a layer of straw or straw mats for insulation. Water-repellent overwintering requires maintaining a water level above 50 cm and a bottom temperature above 0°C. If the pond freezes, the ice must be removed to prevent oxygen deprivation for the eels.

[0003] Large-scale artificial breeding of yellow eels typically involves both breeding ponds and parent rearing ponds. Each autumn, when large-scale artificial breeding of yellow eels concludes, the parent eels are transferred from the cages in the breeding ponds to deeper parent rearing ponds. This not only ensures the eels' safe wintering but also allows for enhanced pre-breeding care the following spring, once the water temperature rises to a suitable level for the eels' feeding. This also optimizes the parent stock, such as removing those with declining reproductive performance and replacing them with those with better physical fitness and reproductive performance, facilitating further artificial breeding the following year. However, using a dry pond overwintering method, where the parent eels are not transferred to parent rearing ponds but only covered with straw or mats within the breeding pond cages, makes it difficult to ensure both the quantity and quality of the parent stock. Therefore, after completing large-scale artificial breeding of yellow eels, the parent eels are removed from the cages in the breeding ponds and transferred to parent rearing ponds for a safe wintering, which helps improve the efficiency of large-scale artificial breeding of yellow eels.

[0004] Removing the eel parents from the breeding ponds and cages is crucial. Manually digging the eel parents from each cage is not only time-consuming and inefficient, but also prone to stress, causing the mucus on the eels to dislodge due to external forces, leading to their death. A method for retrieving the eels that is both non-invasive and minimally damaging, while also being efficient and convenient, is crucial for both production and breeding efficiency. Summary of the Invention

[0005] The present invention provides a method for conveniently and non-invasively recovering parents from net cages after large-scale artificial propagation of swamp eels, thereby enabling the propagated swamp eel parents to safely overwinter, and timely replenishing parents with good propagation performance, and strengthening the cultivation of the parents before the start of large-scale propagation the following year, thereby improving the efficiency of large-scale artificial propagation of swamp eels.

[0006] To solve the above problems, the present invention provides the following technical solutions:

[0007] The embodiment of the present invention provides a method for conveniently and non-invasively recovering parents of yellow eels from cages after large-scale artificial propagation, comprising the following steps:

[0008] Step 1: Prepare the bait net: Cut an old mosquito net into 9-cm squares, take 5-10 live earthworms, and soak them in room-temperature wood ash to coat the worms with a small amount of ash. Wrap the worms with the small squares of mosquito net and tie the four corners tightly with nylon rope to form a small gauze package containing the earthworms. At the same time, prepare a floating trapping net. The net should be a cube-like structure with wire rings at the top and bottom. Four foam blocks are inserted into the top ring, and the height between the foam blocks and the bottom of the net should be 30 cm. Holes are provided at the four corners of the bottom of the net to facilitate entry and exit for the eels.

[0009] Step 2, deepening the pond water: before recapturing the eel parents, stop feeding them for 2 days to make them hungry, then fill the breeding pond with water, deepen the water depth in the cages in the breeding pond from 10-15cm to 50cm, and make sure that the water surface does not overflow the cage opening in the breeding pond, and close the water outlet of the breeding pond;

[0010] Step 3: Place the nets: Start filling the breeding pond with water. In the evening, place the nets in the center of each cage. Place a small gauze package containing earthworms in the center above the top of the nets.

[0011] Step 4, harvesting the parents: lift the net the next day, align one corner of the bottom with the opening of the recycling plastic box, open the hole near the eel, and let the eel slide into the plastic box.

[0012] In an optional embodiment of the present invention, the mesh diameter of the net in step 1 is 6-10 mm.

[0013] In an optional embodiment of the present invention, the body length of the earthworm in step 1 is ≥5 cm.

[0014] In an optional embodiment of the present invention, when deepening the pond water in step 2, it is necessary to ensure that the breeding soil pond is leak-proof.

[0015] In an optional embodiment of the present invention, the net in step 3 needs to be soaked in pond water before use to prevent it from drying out too hard and causing mechanical damage to the eel's body surface.

[0016] In an optional embodiment of the present invention, when placing the net in step 3, it is necessary to check whether the entrance holes at the four corners of the bottom of the net are unobstructed.

[0017] In an optional embodiment of the present invention, when harvesting the parent plants in step 4, it is necessary to first remove the small gauze package on the top of the net.

[0018] In an optional embodiment of the present invention, the specifications of the cage in the breeding soil pond in step 3 are 2m×1m×1m, the bottom of the breeding soil pond has 10cm thick soil, and water hyacinth is planted on the soil.

[0019] Beneficial effect: The embodiment of the present invention provides a method for conveniently and non-invasively recovering the parents of yellow eels from the net cage after large-scale artificial breeding of yellow eels. The method comprises deepening the water in the breeding pond to force the yellow eels to drill out of the soil, placing the nets soaked in pond water in the center of the net cage in the breeding pond, checking and ensuring that the holes at the four corners of the bottom of each net are unobstructed before placing the nets, so that the yellow eels can drill into the nets easily, and the nets are suspended in water. A small gauze package containing earthworms is placed in the center above the top of each net; the yellow eel parents are harvested the next morning, and the yellow eel parents are gradually harvested. The method comprises lifting the net from each net cage, taking out the small package of earthworms placed in the center of the top of the net, making the bottom corner of the net lowest and aligned with the opening of the plastic box for recovering the parents, allowing the trapped eel parents to slide into the corner, and manually opening the hole near the eel to be opened, so that the eel slides into the above-mentioned plastic box from the hole and is counted; the present invention uses a nylon net with earthworm bait suspended in water to trap the eels into the net, thereby achieving the purpose of conveniently and efficiently recapturing the parents after reproduction without causing any damage to the parents, and the parent recapture rate using this method can reach more than 95%. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] In order to more clearly illustrate the technical solutions in the embodiments or the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0021] Figure 1 This is a flow chart of a method for convenient and non-invasive recovery of parents from cages after large-scale artificial propagation of eels provided in an embodiment of the present application. DETAILED DESCRIPTION

[0022] The technical solutions in the embodiments of the present application will be described clearly and completely below in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative work are within the scope of protection of this application. The "upper", "lower", "front", "rear", "left", "right", etc. used in the installation position or direction of the structure or parts of this embodiment are based on the orientation of the given drawings. They are only for the convenience of expression to distinguish the relative positions of the various parts or directions, and do not represent the orientation of the device or functional parts of this embodiment when in use.

[0023] After the completion of large-scale artificial breeding of yellow eels, water temperatures gradually drop in winter, and yellow eel parents need to be transferred from caged earthen ponds to deep water ponds to ensure their safe wintering. Directly digging out the parent eels from the cages in earthen ponds is not only time-consuming and labor-intensive, but also easily causes trauma to the eels. The technical solution of the present invention can solve this technical problem.

[0024] like Figure 1 As shown, the embodiment of the present invention provides a method for conveniently and non-invasively recovering parents from a net cage after large-scale artificial propagation of yellow eels, comprising the following steps:

[0025] Step 1, prepare the net bait: cut the old mosquito net into squares with a side length of 9 cm, take 5-10 fresh earthworms, stick them in room temperature wood ash so that a small amount of wood ash is attached to the surface of the earthworms, then wrap the earthworms with small squares of mosquito net, and tie the four corners tightly with nylon rope to form a small gauze package with earthworms inside; at the same time, prepare a floating trapping net. The net has a cube-like structure with wire rings on the top and bottom. There are 4 foam blocks on the top ring. The height between the foam blocks and the bottom of the net is 30 cm. There are holes in the four corners of the bottom of the net that are easy for eels to enter but difficult to exit.

[0026] Step 2, deepening the pond water: Before recapture of the eel parents, they are first deprived of food for 2 days to starve them. The breeding pond is then filled with water, and the water depth in the net cage is deepened from 10-15 cm to 50 cm. The water surface does not overflow the net cage opening of the breeding pond, and the water outlet of the breeding pond is tightly closed. In this embodiment, the water filling is generally started in the evening. During the general breeding period, the water depth in the net cage is 10-15 cm. Before recapture of the parents, the pond water is generally deepened to 50 cm. The water surface does not overflow the net cage opening, and the water outlet of the breeding pond is tightly closed to ensure that the breeding pond is leak-proof.

[0027] Step 3, placing the net: while water is being poured into the breeding pond, the net is placed in the center of each cage in the evening, and a small gauze package containing earthworms is placed at the center of the top of the net. This embodiment utilizes the characteristic of yellow eels that they hide during the day and come out at night. Hungry yellow eel parents can smell the odor of earthworms and will drill into the net through the holes at the four corners of the bottom of the net that are easy to enter but difficult to exit. After entering the net, the yellow eels will try to eat the small package of earthworms placed at the center of the top, but cannot eat them because of the nylon net, thereby achieving the effect of trapping the yellow eel parents into the net.

[0028] Step 4, Harvesting the Parent Eels: The next day, the net is lifted, with one corner at its lowest position and aligned with the opening of the plastic box for recovering the parent eels. The holes near the eels are then opened, allowing the eels to slide into the plastic box. In this embodiment, on the day of harvesting the parent eels, the nets are lifted one by one from the net cages in the breeding pond, with one corner at its lowest position and aligned with the opening of the plastic box for recovering the parent eels. The trapped eels are then allowed to slide into this corner. The holes near the eels are then opened by hand. Eels, which have a tendency to burrow, will quickly slide into the plastic box through this opening.

[0029] Preferably, the mesh diameter of the net in step 1 is 6-10mm. The body length of the earthworm in step 1 is ≥5cm. When deepening the pond water in step 2, it is necessary to ensure that the breeding soil pond is leak-proof. The net in step 3 needs to be soaked in pond water before use to prevent it from drying out too hard and causing mechanical damage to the surface of the eel. When placing the net in step 3, it is necessary to check whether the entrance holes at the four corners of the bottom of the net are unobstructed. When harvesting the parents in step 4, it is necessary to first remove the small gauze package above the top of the net. The breeding soil pond in step 3 has a specification of 2m×1m×1m, and there is 10cm thick soil at the bottom of the breeding soil pond, and water hyacinth is planted on the soil.

[0030] Example 1

[0031] The breeding ponds contain 1,000 cages, each measuring 2m x 1m x 1m. The bottoms of the cages are covered with approximately 10cm of soil, planted with water hyacinths. The water level inside the cages is approximately 10cm. During the initial breeding phase, each cage houses three male and two female eels, for a total of 5,000 eels. During the artificial breeding process, if an eel dies in a cage, it will be promptly replaced with a fertile eel to ensure a consistent population. After the large-scale artificial breeding phase is complete, and once the water temperature gradually decreases in late September, the eels will be recaptured and transferred to the parent rearing ponds.

[0032] From the time the plan to recapture the broodstock begins, feeding the nets in the breeding ponds and cages will cease. During this period, 1,000 of the aforementioned nets will be prepared and pre-soaked in the ponds to prevent mechanical damage to the eels' bodies caused by the nets drying out and becoming too hard when retrieving the broodstock.

[0033] After 2 days of fasting, open the water inlet of the breeding pond and fill it with water until the water depth in the breeding pond cage reaches about 50 cm.

[0034] In the afternoon, fresh earthworms (body length ≥ 5 cm) were collected, weighing approximately 4 kg. Two old mosquito nets were cut into 9-cm squares with scissors, totaling 1,000 pieces. Five to eight fresh earthworms wrapped in room-temperature wood ash were wrapped around each square of mosquito net, and the four corners of the squares were tied with nylon string.

[0035] Place one net cage per net cage soaked in pond water until all the net cages in the breeding pond are filled. Before placing the nets, check and ensure that the four holes at the bottom of each net are unobstructed to facilitate the eels to drill into the net. Place the net in the center of the net cage and suspend it in the water. Place a small gauze package with earthworms in the center above the top of each net.

[0036] The next morning, we started harvesting the eel parents. We lifted the nets from each cage one by one and took out the small package of earthworms placed in the center above the top of the net. We made the bottom corner of the net the lowest and aimed it at the opening of the plastic box for recovering the parents. We let the trapped eel parents slide into the corner and used our hands to open the hole near the eel so that the eels could slide into the plastic box from the hole and be counted.

[0037] Recapture Results: This method recaptured 957 yellow eel parents, achieving a 95.70% recapture rate. Forty-three eels failed to enter the net or emerged from the soil. The recaptured eels had a 100% survival rate and showed no surface trauma. The process involved six people and took 30 hours.

[0038] The comparative experiment used bare hands to dig out the eel parents from the breeding earthen pond cages. The pond water needed to be drained, the water hyacinth in the cage was moved to the corner of the cage, or even the water hyacinth was pulled out and temporarily placed outside the cage. Then the soil at the bottom of the cage was turned over, and the eels were caught by bare hands and put into a plastic box and counted.

[0039] Recapture results: A total of 772 eel parents were recaptured using this method, with a recapture rate of 77.20%. In the process of digging out the eel parents by hand, the net cages were easily broken, and many eel parents drilled out of the net cages and ran into the breeding ponds, making them difficult to capture again. Even among the eel parents that were recaptured, 84 died due to mechanical damage, and the survival rate was only 68.80%. It required 6 people and took 120 hours.

[0040] Taking 1,000 breeding cages in earthen ponds as an example, the comparison of the effects of the two methods of recapturing yellow eel parents is shown in the table below:

[0041] Table 1 Comparison of two parent recapture methods

[0042] Recapture rate Survival rate Input costs Digging with bare hands 77.20％ 100％ 6 people 30 hours Deepen the pond water and trap with nets 95.70％ 68.80％ 6 people 120 hours

[0043] The present invention provides a method for conveniently and non-invasively recovering eel parents from net cages after large-scale artificial propagation of eels. The method deepens the water in the breeding pond to force the eels out of the soil. The eels are then ensnared in a nylon net containing earthworm bait suspended in water, thereby conveniently and efficiently recovering the post-breeding parents without causing any trauma. The method achieves a high parent recovery rate, minimal or no damage to the parents, and low investment costs.

[0044] The above shows and describes the basic principles, main features and advantages of the present invention. It should be understood by those skilled in the art that the present invention is not limited to the above embodiments. The above embodiments and descriptions are merely preferred examples of the present invention and are not intended to limit the present invention. Various changes and improvements may be made to the present invention without departing from the spirit and scope of the present invention, and such changes and improvements fall within the scope of the present invention. The scope of protection claimed in the present invention is defined by the appended claims and their equivalents.

Claims

1. A method for conveniently and non-invasively recovering the parent eels from the cages after large-scale artificial propagation of eels, characterized in that: The following steps are involved: Step 1: Prepare the bait net: Cut an old mosquito net into 9-cm squares, take 5-10 live earthworms, and soak them in room-temperature wood ash to coat the worms with a small amount of ash. Wrap the worms with the small squares of mosquito net and tie the four corners tightly with nylon rope to form a small gauze package containing the earthworms. At the same time, prepare a floating trapping net. The net should be a cube-like structure with wire rings at the top and bottom. Four foam blocks are inserted into the top ring, and the height between the foam blocks and the bottom of the net should be 30 cm. Holes are provided at the four corners of the bottom of the net to facilitate entry and exit for the eels. Step 2, deepening the pond water: before recapturing the eel parents, stop feeding them for 2 days to make them hungry, then fill the breeding pond with water, deepen the water depth in the cages in the breeding pond from 10-15cm to 50cm, and make sure that the water surface does not overflow the cage opening in the breeding pond, and close the water outlet of the breeding pond; Step 3: Place the nets: Start filling the breeding pond with water and place the nets in the center of each cage in the evening. Place a small gauze package containing earthworms in the center above the top of the nets. Step 4, harvesting the parents: lift the net the next day, align one corner of the bottom with the opening of the recycling plastic box, open the hole near the eel, and let the eel slide into the plastic box.

2. The method for conveniently and non-invasively recovering the parent eels from the net cages after large-scale artificial propagation of the eel according to claim 1, characterized in that: The mesh diameter of the net in step 1 is 6-10 mm.

3. The method for recovering the parents of the eel from the cage conveniently and non-invasively after large-scale artificial propagation of the eel according to claim 1, characterized in that: The body length of the earthworm in step 1 is ≥5 cm.

4. The method for recovering the parents of the eel from the cage conveniently and non-invasively after large-scale artificial propagation of the eel according to claim 1, characterized in that: When deepening the pond water in step 2, make sure the breeding soil pond is leak-proof.

5. The method for recovering the parents of the eel from the cage conveniently and non-invasively after large-scale artificial propagation of the eel according to claim 1, characterized in that: The net in step 3 needs to be soaked in pond water before use to prevent it from drying out and causing mechanical damage to the eel's body surface.

6. The method for conveniently and non-invasively recovering the parent eels from the net cages after large-scale artificial propagation of the eel according to claim 1, characterized in that: When placing the net in step 3, check whether the holes at the four corners of the bottom of the net are unobstructed.

7. The method for conveniently and non-invasively recovering the parent eels from the net cages after large-scale artificial propagation of the eel according to claim 1, characterized in that: When harvesting the parent plants in step 4, first remove the small gauze package on top of the net.

8. The method for recovering the parents of the eel from the cage conveniently and non-invasively after large-scale artificial propagation of the eel according to claim 1, characterized in that: The cage in the breeding soil pond in step 3 has a specification of 2m×1m×1m. There is 10cm thick soil at the bottom of the breeding soil pond, and water hyacinth is planted on the soil.

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