Method for inducing sex differentiation of Japanese eels

Abstract

The invention relates to a method for inducing sex differentiation of Japanese eels, which comprises the following steps: (1) collecting glass eels of Japanese eels, and temporarily culturing the glass eels in a circular glass fiber reinforced plastic water tank with the temporary culture density of 28-30 / m < 3 > in each water tank and the temporary culture water temperature of 17.6 + / -1.0 DEG C; (2) transferring the glass eels into other circular glass fiber reinforced plastic water tanks after the glass eels are temporarily raised for 6-8 days, and placing inflation heads in the water tanks to keep the dissolved oxygen in the water body to be 6.0 mg / L or above; a circulating filtering device is arranged above the water tank; laying a shading net at the top of the water tank for shading; placing a PVC water pipe at the bottom of the water tank; the water temperature is 17.6 + / -1.0 DEG C; 5 mg / kg of estradiol is added into the special bait for the glass eels to serve as induction feed, feeding is conducted once a day, and water is changed once a day. The method provided by the invention can successfully induce sex differentiation of eels, and provides a way for obtaining female eel parents in artificial propagation.

Description

Technical Field

[0001] This invention belongs to the field of aquaculture technology, and specifically relates to a method for inducing sex differentiation in Japanese eels. Background Technology

[0002] The Japanese eel, also known as the river eel or eel, is a typical anadromous fish that breeds in the deep sea and grows in freshwater. It is distributed in the coastal waters and rivers of my country, Japan, South Korea, and the Philippines. The eel is currently the only farmed species in the world that relies entirely on natural seedlings for aquaculture; its artificial breeding technology has not yet reached industrial-scale production. For a long time, my country's artificial breeding research on eels has mainly used wild-caught silver eels as broodstock. However, with the decline of natural eel resources and strict controls on fishing, the number of wild silver eels available for breeding research is severely insufficient; at the same time, the varying developmental stages of wild silver eels pose challenges to artificial breeding research.

[0003] Sex differentiation, as the initiating regulatory node of gonadal development in bony fishes, determines the direction of gonadal development and influences the gonadal maturation process through endocrine feedback regulation. Under artificial breeding conditions, eels need to be raised to 5-6 years old before they can be used for induced maturation and spawning, resulting in a long breeding cycle, high breeding costs, and a surplus of male eels compared to females. Therefore, there is a need to develop an artificial feminization induction method to shorten the gonadal development cycle of eels and promote earlier gonadal differentiation. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide a method for inducing sex differentiation in Japanese eels, so as to shorten the development cycle of eel gonads and promote their early gonadal differentiation.

[0005] This invention provides a method for inducing sex differentiation in Japanese eels, comprising the following steps:

[0006] (1) Collect Japanese glass eels and temporarily raise them in circular fiberglass tanks for 6-8 days, with a stocking density of 28-30 eels / m² per tank. 3 The temporary holding water temperature is 17.6±1.0℃;

[0007] (2) After the temporary rearing period, the glass eels are transferred to other round fiberglass tanks. An air inlet is placed in the tank to maintain dissolved oxygen in the water above 6.0 mg / L. A circulating filter is placed above the tank to maintain the circulation of the water. A shade net is laid on the top of the tank to block light, and PVC water pipes are placed at the bottom of the tank to provide hiding places for the glass eels. The water temperature is 17.6±1.0℃. Feed is given once a day and uneaten food is removed in time. The water is changed once a day.

[0008] Preferably, the glass eel in step (1) has an average total length of 5.6 cm and an average weight of 0.1 g.

[0009] Preferably, in step (1), the water tank is disinfected by soaking in potassium permanganate solution before temporarily raising the glass eels, and then the water tank is cleaned with filtered and aerated tap water; the diameter of the water tank used for temporary raising is 1.4 to 1.6 m and the water depth is 0.9 to 1.1 m.

[0010] Preferably, the water body mentioned in steps (1) and (2) is fresh water.

[0011] Preferably, the diameter of the water tank in step (2) is 70-90 cm, and the stocking density of glass eels in each water tank is 15-25 eels / m². 3 The water depth is 50-70cm.

[0012] Preferably, the feed in step (2) is 5 mg / kg estradiol (E2) added to glass eel special feed, fed at 1:30 pm every day, with a daily feeding amount of 3% of the body weight of the glass eels in the tank, and an induction period of 120 to 270 days.

[0013] More preferably, the glass eel bait is Tianma brand "Yiduomei" glass eel bait.

[0014] Preferably, the daily water replacement volume in step (2) is 1 / 3 of the water volume in the tank.

[0015] Preferably, the number of air inflators in step (2) is adjusted based on the size of the water tank.

[0016] Preferably, step (2) includes cleaning and replacing the filter cloth in the circulating filter device daily to keep the filter cloth clean.

[0017] Preferably, in step (2), one to two PVC water pipes with a diameter of 10cm and a length of 30cm are placed at the bottom of each water tank.

[0018] Beneficial effects

[0019] (1) This invention uses glass eel juveniles as experimental subjects to induce sex differentiation, which has low cultivation cost and good induction effect.

[0020] (2) In this invention, estradiol is added to the special feed for glass eels for induction. The glass eels eat well, which is conducive to inducing sex differentiation in glass eels.

[0021] (3) The present invention screens a suitable induction dose to ensure that it can effectively induce the fish while reducing damage to the glass eel.

[0022] (4) Based on the living habits of glass eels, this invention provides habitats and breeding environments for glass eels. After a period of breeding, it successfully induces sex differentiation in eels, providing a way to obtain female eel parents in artificial breeding. Attached Figure Description

[0023] Figure 1 This image shows the oocytes of a female glass eel developing to the early oil droplet stage 120 days after feeding.

[0024] Figure 2 This image shows the oocytes of a female glass eel developing to the late oil droplet stage after 270 days of feeding. Detailed Implementation

[0025] The present invention will be further illustrated below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Furthermore, it should be understood that after reading the teachings of this invention, those skilled in the art can make various alterations or modifications to the invention, and these equivalent forms also fall within the scope defined by the appended claims.

[0026] Example

[0027] The method for inducing sex differentiation in Japanese eels in this embodiment includes the following steps:

[0028] (1) Collect several Japanese glass eels, with an average total length of 5.6 cm and an average weight of 0.1 g. Transport them to the laboratory in oxygenated plastic bags, with 30-50 glass eels per bag. The number can be adjusted according to the size of the plastic bag. Disinfect the circular fiberglass tanks by soaking them in a 5 ppm potassium permanganate solution. After soaking, rinse the tanks with filtered and aerated tap water. The glass eels are temporarily housed in circular fiberglass tanks with a diameter of 1.5 m. The holding water temperature is 17.6 ± 1.0 ℃, the water depth is 1 m, and the holding density is 28-30 eels / m². 3 .

[0029] (2) After 7 days of temporary rearing, the glass eels were transferred to other round fiberglass tanks with a diameter of 80cm. The water used for rearing was freshwater, and the stocking density in each tank was 15-25 eels / m². 3The fish density can be adjusted according to actual conditions, maintaining a water depth of 60cm. A layer of black shade netting should be laid on top of the tank to block light. The water temperature should be 17.6±1.0℃. Place 1-2 PVC pipes, 10cm in diameter and 30cm long, at the bottom of the tank to provide hiding places for the glass eels. Add estradiol to Tianma brand "Yiduomei" glass eel-specific feed and feed once daily at 1:30 PM. The daily feed amount should be 3% of the fish's body weight in each tank. Remove uneaten food promptly and change the water once daily, replacing 1 / 3 of the tank's volume. Place 4-5 aerators at different locations in the water, such as the middle and bottom. The number of aerators can be adjusted according to the size of the fiberglass tank, maintaining dissolved oxygen levels above 6.0mg / L. Place a circulating filter above the tank to maintain water circulation. Clean and replace the filter cloth in the circulating filter daily to keep it clean.

[0030] Based on previous research, adding a low dose of 1 mg / kg estradiol to glass eel-specific feed resulted in low sex differentiation, prolonged induction time, increased induction costs, and failure to achieve the desired effect. Adding a high dose of 10 mg / kg estradiol increased the number of males, decreased the feminization rate, and caused liver damage in some fish, failing to meet the requirement of obtaining more female eels through induction. Therefore, using Tianma brand "Yiduomei" glass eel-specific feed with 5 mg / kg estradiol added, after 120 days of feeding, sex differentiation began in the glass eels, with female individuals' oocytes developing to the early oil droplet stage, such as... Figure 1 As shown; after 270 days of feeding, both total length and weight increased significantly, with females accounting for 80% of the individuals. The oocytes of the females developed to the late oil droplet stage, as shown... Figure 2 As shown, the ovaries are well-developed, and the induction effect is obvious.

Claims

1. A method for inducing sex differentiation in Japanese eels, comprising the following steps: (1) Collect Japanese glass eels and temporarily hold them in circular fiberglass tanks for 6-8 days; the holding density is 28-30 eels / m² per tank. 3 The temporary holding water temperature is 17.6±1.0℃; (2) After the temporary rearing period, the glass eels are transferred to other round fiberglass tanks. An air inlet is placed in the tank to maintain dissolved oxygen in the water above 6.0 mg / L. A circulating filter is placed above the tank to maintain the circulation of the water. A shade net is laid on the top of the tank to block light, and PVC water pipes are placed at the bottom of the tank to provide hiding places for the glass eels. The water temperature is 17.6±1.0℃. Feed is given once a day and uneaten food is removed in time. The water is changed once a day.

2. The method for inducing sex differentiation in Japanese eels according to claim 1, characterized in that, The glass eel described in step (1) has an average total length of 5.6 cm and an average weight of 0.1 g.

3. The method for inducing sex differentiation in Japanese eels according to claim 1, characterized in that, Before temporarily raising glass eels in step (1), the water tank is disinfected by soaking in potassium permanganate solution, and then the water tank is cleaned with filtered and aerated tap water. The water tank used for temporary raising has a diameter of 1.4 to 1.6 m and a water depth of 0.9 to 1.1 m.

4. The method for inducing sex differentiation in Japanese eels according to claim 1, characterized in that, The water tanks in step (2) have a diameter of 70-90 cm, and the stocking density of glass eels in each tank is 15-25 eels / m². 3 The water depth is 50-70cm.

5. The method for inducing sex differentiation in Japanese eels according to claim 1, characterized in that, The feed in step (2) is 5 mg / kg estradiol added to glass eel special feed. It is fed at 1:30 pm every day. The daily feeding amount is 3% of the body weight of the glass eels in the tank. The induction period is 120 to 270 days.

6. The method for inducing sex differentiation in Japanese eels according to claim 1, characterized in that, The daily water replacement volume in step (2) is 1 / 3 of the water volume in the tank.

7. The method for inducing sex differentiation in Japanese eels according to claim 1, characterized in that, In step (2), place 1 to 2 PVC water pipes with a diameter of 10cm and a length of 30cm at the bottom of each water tank.

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