Method for breeding one-year-old precocious female crabs in rice field in East China

Abstract

The invention discloses a method for breeding one-year-old precocious female crabs in a rice field in East China. A cross-shaped ditch with the width of 0.3-4 m and the depth of 0.3-0.8 m is dug in the middle of the rice field, alternanthera philoxeroides or operculate cleistocalyx water plants are planted in the ditch, and a small amount of waterweed or hydrilla verticillata is matched; intensively and temporarily rearing the river crab megalops in the fry pond for more than or equal to 45 days; after rice field seedlings turn green and the river crab megalopa develops to six-stage juvenile crabs, the average water temperature of the rice field is larger than or equal to 18 DEG C, and six-stage female juvenile crabs are selected and put into rice field ditches; the female river crab juvenile crabs mainly depend on aquatic plants, rice field plankton and benthic organisms to provide bait within 20 days before breeding in the rice field, and when the number of waterweed / hydrilla verticillata aquatic plants is greatly reduced, juvenile crab feed is fed; fattening is started after the proportion of one-year precocious puberty individuals of the river crabs reaches 70%, fishing is started after fattening is conducted for 20 days, and rice is harvested after fishing is completed. By means of the method, the one-year-old precocious puberty rate of the female crabs bred in the rice field is larger than or equal to 90%, the one-year-old precocious puberty crabs per mu are larger than 50 jin,

Description

Technical Field

[0001] The invention relates to the technical field of rice planting and paddy field aquaculture, and in particular to a method for culturing one-year-old sexually precocious female crabs in paddy fields in East China, especially East China, South China or Southwest China. Background Art

[0002] The Chinese mitten crab (Eriocheir sinensis) is one of the most important economic aquaculture species in my country's freshwater fisheries, with a growth cycle of 2 years. The first year is for the breeding of crab seedlings and larvae to crabs (crab seed cultivation stage), and the second year is for the breeding of crabs to adult crabs (adult crab cultivation stage). It has formed a stable industrial chain from crab seed breeding, crab seed cultivation, adult crab farming and product deep processing, and has become one of the important ways to improve the quality and efficiency of agricultural and fishery production in various places. However, during the crab seed cultivation stage, the problem of precocious maturity of the Chinese mitten crab in the first year caused by the combined effects of multiple factors such as salinity, temperature, nutrition, and germplasm has always plagued the healthy development of the river crab industry.

[0003] One-year-old precocious crabs (also called early-maturing crabs, commonly known as old crabs) have small individual sizes (15-35g) and low edible value; secondly, their gonads have matured, they basically do not grow and have a high mortality rate, so they cannot be used for adult crab farming the following year. Therefore, the commercial performance of one-year-old precocious crabs is poor, and breeders regard them as objects to be eliminated during the farming process. However, with the development of crab pre-cooked products and deep processing industries, processed products such as "drunk crabs", "spicy crabs", "crab roe sauce", and "crab roe powder" developed with small-sized crabs as the focus are widely favored by consumers, making the commercial value of one-year-old precocious crabs, especially large-sized female crabs weighing more than 35g, continue to increase. However, it is costly to raise precocious crabs in crab ponds, and the density is too high, the precocious rate is low, and the specifications are not uniform, so the effect is not good.

[0004] The rice-crab farming model is an ecological agricultural model formed by the organic combination of planting and breeding based on the biological characteristics of rice and Chinese mitten crab. Chinese mitten crabs loosen the soil, weed and remove insects for rice fields, and effectively reduce the number of ineffective tillers of rice, promote the absorption of nutrients by rice roots, and at the same time, rice also provides rich natural bait and a good habitat and growth environment for river crabs. Therefore, rice-crab farming has the characteristics of improving resource utilization and comprehensive benefits. Usually, this farming model is mainly concentrated in high-latitude cold areas such as Northeast China and Ningxia, and mainly breeds one-year-old crabs (clip crabs) in rice fields. That is, after rice is transplanted and seedlings are planted, large-eyed larvae are released into the rice fields, and the clip crabs are caught in October and November, and they are temporarily raised in high-density concentrated areas for the winter. They are then released into the rice fields again in the spring of the second year to breed adult crabs.

[0005] Although the East China region, especially the East China region, is the main production area of ​​river crabs in my country, there are very few studies on rice-crab farming in the region. This is mainly because the breeding period of river crabs in the East China region is usually from early May to the end of November, while the growth cycle of commonly cultivated rice varieties in the region is from June to October, and rice is harvested in mid-to-early November. When river crab megalopause (crab seedlings) are released, rice has not yet been transplanted; when rice needs to be harvested, river crabs have not yet reached the fishing period; therefore, it is difficult to balance river crab seed cultivation and rice planting, and rice-crab farming in the region is not conducive to crab seed cultivation.

[0006] In order to expand the area of ​​arable land, according to the requirements of arable land reclamation, the area of ​​the original crab pond is reduced. In order to increase the additional income of grain planting and improve the enthusiasm for returning ponds to farmland, it is necessary to develop a rice-crab co-cultivation model suitable for the region. Therefore, the present invention provides a method for breeding one-year-old precocious female crabs in rice fields in East China, especially in East China. This model has strong market potential and high economic benefits, and is worthy of further exploration and application promotion. Summary of the invention

[0007] The purpose of the present invention is to address the defects in the prior art and provide a method suitable for East China, especially for breeding large-sized one-year-old precocious crabs in East China, so as to solve the problems of low yield and non-uniform specifications of breeding one-year-old precocious crabs (commonly known as "old man crabs").

[0008] Based on the research and development of traditional rice field-river crab symbiosis technology, the present invention has developed a method for breeding large-sized one-year-old sexually precocious female crabs in rice fields in East China. The proportion of one-year-old sexually precocious crabs cultivated exceeds 90%, and the average size is ≥30g.

[0009] The technical problem to be solved by the present invention can be achieved by the following technical solutions:

[0010] A method for breeding one-year-old precocious female crabs in rice fields in East China, comprising the following steps:

[0011] (1) Dig a cross-shaped trench in the middle of the rice field and plant the following aquatic plants in the trench:

[0012] (a) Water Peanuts and / or Bighead Carrots; with,

[0013] (b) Elodea and / or Hydrilla verticillata;

[0014] (2) Transplanting rice seedlings into rice fields;

[0015] (3) When the rice seedlings turn green and the water temperature is ≥18°C, healthy female crab larvae are placed in the cross grooves of the rice fields;

[0016] (4) After the female crabs have been cultured in the rice field for 15-20 days, they are fed with crab culture feed; preferably, after 20 days of culture, they are fed with crab culture feed;

[0017] (5) When the one-year-old sexual maturity rate reaches ≥70%, continue to feed and fatten the fish, and start harvesting after 20 days of fattening.

[0018] Preferably, rainfall is applied to harvest the rice after the harvesting is completed.

[0019] There is no restriction on the order of steps (1) and (2), and they can be performed in reverse order or simultaneously.

[0020] In step (1), the cross groove is 0.3-4m wide and 0.3-0.8m deep, and the total area of ​​the cross groove accounts for ≤10% of the entire rice field area. The cross groove in the middle of the rice field is convenient for drying the rice field and hiding the young crabs during high temperatures. Preferably, the depth of the cross groove is 0.4-0.6m; in a preferred embodiment of the present invention, the depth is 0.5m.

[0021] In step (1), the planting ratio of aquatic plants (a) to (b) is 3-20:1, preferably 5-10:1. Specifically, the aquatic plants planted are at least one of the following methods;

[0022] Method A: Water peanuts with a small amount of Elodea; the ratio is 3-20:1;

[0023] Method B: Water peanuts with a small amount of Hydrilla verticillata; the ratio is 3-20:1;

[0024] Method C: Bighead carp with a small amount of Elodea; the ratio is 3-20:1;

[0025] Method D: Bighead carp, with a small amount of Hydrilla verticillata; the ratio is 3-20:1.

[0026] Preferably, the quantity ratio is 5-10:1.

[0027] In step (3), the average size of the crablets is ≥1g / crab, and the stocking density is 22250-75000 / hm2. 2 . Preferably 30,000-70,000 / hm 2 .

[0028] In step (3), the crablets develop to stage six or above.

[0029] The crab fry can be released only after the rice seedlings turn green. If they have not turned green yet, you can wait. Otherwise, releasing crab fry too early will easily cause the roots of the rice seedlings to be eaten by crab fry, affecting the growth of rice.

[0030] The method for obtaining female crab larvae is to place megalopa larvae in a crab breeding pond at a rate of ≤7 jin per mu, and temporarily raise them for 45-60 days. Preferably, the amount of megalopa larvae placed is 4-7 jin / mu, and more preferably 5-6 jin / mu. When they grow to the sixth stage of crab larvae (just enough to distinguish male and female), they are caught with ground traps, and all-female crab larvae with good vitality and healthy limbs are selected and placed in rice fields.

[0031] If the stocking density of large-eyed juveniles is too high, their growth will be too slow, making it difficult to connect with the later rice crop. If the stocking density is too low, the temporary production will be low.

[0032] In the early stage of temporary rearing, plankton is cultivated as natural bait by fertilizing the water, and special feed for crab farming is fed at the same time. When the rice seedlings turn green, the water temperature is ≥18℃, and the river crabs have developed to at least the sixth stage of juvenile crabs, healthy females are selected and released into the rice field ditch.

[0033] A preferred method for temporary rearing is to lay water peanuts in the middle of the crab breeding pond and plant verticillium or bighead water grass in the surrounding ditch. After releasing the megalopa larvae, feed them with special feed for crab breeding and add fertilizer water to increase pond plankton as food.

[0034] Furthermore, adjustments need to be made depending on the water level, water temperature and bait feeding conditions so that the breeding cycle is ≥ 45 days and the crabs grow to the size of sixth-stage crab larvae to avoid long breeding time and difficulty in connecting with the rice transplanting crop.

[0035] The selection of stage 6 crab fry from the temporary pond needs to be done quickly, in a cool or shady area, to avoid high temperatures or direct sunlight that can affect the survival rate. At the same time, small amounts of crab fry should be caught from the temporary pond multiple times, and they should be placed in the rice field within 1 hour after selection, to prevent the crab fry from being out of water for too long, which may lead to an increase in the mortality rate of the crab fry after being put into the pond.

[0036] In step (2), rice is planted in blocks, and the spacing between plants and rows is uniform as much as possible, so as to facilitate ventilation between rice and facilitate the artificial passage for feeding feed. In the daily management of rice, no highly toxic pesticides are used to avoid affecting the growth and survival of river crabs.

[0037] In step (3), when releasing crab larvae, the coverage area of ​​aquatic plants is 35%-70% of the cross ditch area, preferably 50%-70%; the rice seedlings are flooded with 20-40cm of water to prevent the water temperature of part of the beach from being too high due to too low water level, causing the crabs to die on the beach. The crab larvae are released in the cross ditch of the rice field to prevent the crab larvae from being stressed and dying from high temperature or being sunburned on the rice field platform.

[0038] A preferred solution for rice transplanting and daily management is: fertilize on the rice planting platform and then turn the soil. Preferably, apply compound fertilizer (10kg / mu) and then turn the soil. Rice transplanting is carried out in June-early July, with a plant spacing of ≥16cm and a row spacing of ≥30cm. Rice is planted in blocks, and all rice seedlings are planted except for the cross furrow. One row is planted every 10 meters, leaving a passage as a passage for artificial feeding and crab activities.

[0039] In step (4), Elodea and / or Hydrilla verticillata are used as indicator aquatic plants for feeding. Female river crab larvae feed on water peanuts and paddy field plankton and benthic organisms in the first 0-20 days (preferably 0-20 days) of culture in rice fields. When the number of Elodea / Hydrilla verticillata aquatic plants decreases significantly, it indicates that the pond bait is insufficient and it is necessary to increase the feeding feed. Feed once every 1-2 days. Preferably, feed once a day. Feed crab breeding feed, the specifications of which increase from crushed material to 2.5mm, the feed protein content is 35-42%, and the feeding amount each time is 1% to 3% of the total weight of the crab larvae.

[0040] Preferably, in the first 20 days after the crabs are placed in the rice field, if the water quality is relatively rich, no feeding is required, and the crab seedlings eat natural bait and aquatic plants. If the water quality is thin, or if there is a large reduction in the amount of Elodea or Hydrilla verticillata in the ditch, you can gradually start feeding. Put 2-3 feeding tables in each cross ditch of the rice field, and flexibly adjust the feeding amount according to the feeding situation of the feeding table.

[0041] During the breeding cycle, the water level from the bottom of the cross ditch to the water surface is ≤1 meter, and the water level in the rice planting part is maintained at 20-40cm.

[0042] In step (5), the criteria for judging sexual precocity of the first-year rice crabs are that the female umbilicus completely covers the abdomen, and the umbilicus and carapace are relatively tilted. The male crabs are fully covered with large claw hairs, and the bottom of the umbilicus is obviously convex, indicating maturity.

[0043] When the proportion of one-year-old precocious crabs reaches 70%-82%, continue to feed them for 10-20 days before starting to harvest. The protein content of fattening feed should not be less than 38%, thereby improving the quality of precocious crabs. If the one-year-old precocious crabs are harvested too early, their weight and fatness will be poor. If they are harvested too late, they will easily kill each other, reducing the yield.

[0044] The fishing method is ground trap fishing, mainly using a ground trap with a mesh size of 3 cm. Preferably, trap fishing is combined with trap fishing, and traps are dug near the cross ditch of the rice field to trap the one-year-old precocious crabs by taking advantage of the fact that they crawl ashore in October. After the one-year-old precocious crabs in the rice field are basically caught, the water level of the rice field is gradually lowered to allow the remaining young crabs to enter the cross ditch, and ground traps are used to continue fishing in the ditch.

[0045] If it is inconvenient to dig traps, you can catch fish by setting up more ground traps.

[0046] After the first-year precocious crabs are caught, rice is harvested. Usually, rice is harvested by harvester in late October or early November; if the rice fields are moist, they can be dried for about a week before harvesting.

[0047] In step (1), the cross ditch is opened in the middle of the rice field or pond, which is not only conducive to the crabs entering the rice planting area from the ditch at night (favorable for rice-crab interaction), but also convenient for ventilation inside the paddy field and providing a channel for artificial feeding; when the water level in the rice field is lowered, the crabs on the rice field platform will follow the water into the cross ditch, which is convenient for crab fishing. According to the "Technical Specifications for Integrated Rice and Fishery Breeding - General Principles of Part 1", the total area of ​​the cross ditch shall not exceed 10% of the area of ​​the field, which is beneficial to the marginal effect of rice, and basically will not affect the per-acre yield of rice, and at the same time can produce large-sized one-year-old early-maturing crabs.

[0048] In step (1), water peanut and big-headed crab type water plants are both high temperature resistant water plants, have good water purification effects, and provide shelter for crabs to avoid natural enemies and the same species, thereby improving the survival rate of breeding. Elodea and Verticillium are small feeding water plants for river crabs. Proper combination of planting these two water plants is conducive to supplementing bait and reducing the bait coefficient. Different water plants can be planted in blocks with a spacing of about 0.5-1 meters to facilitate the free movement of river crabs and prevent the water plants from being too dense and causing hypoxia at night. Block planting can be carried out in boxes, with a spacing of 0.5-1 meters between the boxes. 6-8 water plants are planted in each square planting area, and each plant is ≥15cm apart.

[0049] In step (2), the sparser the density of crabs released into the rice field, the higher the rate of early maturity of the first-year crabs and the larger the size. It is recommended that the release density should not be less than 1500 crabs / mu (22500 crabs / hm2). 2 ) to avoid too low production.

[0050] The technology of the present invention is suitable for use by rice planting, river crab breeding enterprises or farmers, and not only provides the market with super-large one-year-old early-maturing crabs, thereby increasing the comprehensive benefits of rice planting, reducing the amount of pesticides and fertilizers used in rice planting, and reducing the cost of rice planting. The method can be widely promoted in East China during the rice planting period from June to November, such as in rice fields in East China.

[0051] The advantages and positive effects of the present invention are:

[0052] (1) Through the field engineering transformation of rice fields, ventilation of rice-crab fields can be achieved, feeding and management can be facilitated, and high-yield and large-sized one-year-old precocious crabs can be easily cultivated; the yield per mu exceeds 50 jin, and the size exceeds 30g.

[0053] (2) By temporarily raising crab seedlings to the sixth stage and then transplanting them to rice fields, long-distance transportation and external purchase of seedlings can be avoided, mortality can be reduced, and breeding efficiency can be improved. At the same time, the seedlings can be temporarily raised to the sixth stage of crab larvae, which has low feed costs and high yields.

[0054] (4) All-female snap crabs are used for breeding. The proportion of one-year-old precocious crabs is high, which can reach more than 90%, and the size is large and the yield is high. In addition to harvesting one-year-old precocious crabs, normal snap crabs can also be obtained for adult crab breeding in the second year.

[0055] (5) Planting water peanuts or bighead carp in the cross-shaped grooves of rice fields, together with Hydrilla verticillata or Elodea, can not only purify the water quality and provide a hidden environment for river crabs to molt, but also Hydrilla verticillata and Elodea can be directly used as natural bait for river crabs, thereby reducing the feed coefficient, saving feed feeding costs, and improving aquaculture efficiency.

[0056] (6) This method found that one-year-old precocious crabs cultured in rice fields mainly rely on aquatic plants and benthic animals for food in the early stage, and mainly rely on feed in the later stage. Therefore, a small amount of feeding or no feeding is given in the early stage, and more feed is given in the later stage. This precise feeding strategy is conducive to saving feed costs during the breeding cycle, and this method has great application and promotion value. BRIEF DESCRIPTION OF THE DRAWINGS

[0057] Figure 1 Design of field block structure for one-year-old precocious crabs in rice fields;

[0058] Figure 2 This is the distribution map of male and female crablets at different stages of one-year-old precocious crabs (the sixth stage is the easiest to distinguish);

[0059] Figure 3 The proofing photos of the experiment site for one-year-old precocious crabs;

[0060] Figure 4 Digging traps on the edge of rice fields to catch one-year-old precocious crabs with lights

[0061] Figure 5 Example 1 Effect of stocking density on the average body weight of female crabs at the one-year-old precocious crab and one-year-old juvenile crab stage

[0062] Figure 6 Effects of stocking density of juvenile crabs on gonadal index and hepatopancreas index of one-year-old precocious females of Chinese mitten crab

[0063] Figure 7 Effects of two juvenile crab stocking densities on the body mass distribution of one-year-old precocious crabs

[0064] Figure 8 Effects of different stocking densities of Eriocheir sinensis on the growth height of rice plants

[0065] Fig. 9 Comparison of the food contribution rate of the same food to Chinese mitten crabs at different stocking densities. DETAILED DESCRIPTION

[0066] The present invention is described in detail below in conjunction with specific embodiments. The following embodiments will help those skilled in the art to further understand the present invention, but are not intended to limit the present invention in any form. It should be noted that, for those of ordinary skill in the art, several changes and improvements can also be made without departing from the concept of the present invention. These all belong to the protection scope of the present invention.

[0067] The present invention will be further described below in conjunction with embodiments:

[0068] Example 1

[0069] This experiment was conducted at the Shuxin Town Industry-University-Research Base of Shanghai Ocean University. Two rice fields with similar conditions and independent water inlet and drainage were selected as experimental fields, with an area of ​​334 m 2 .

[0070] The design of field structure for one-year-old early-maturing crabs in rice fields Figure 1 As shown: a cross ditch is dug in the middle of the rice field, with a depth of 0.5m and a width of 2-4m, and its area does not exceed 10% of the total area of ​​the rice field. The cross ditch is a crab ditch, which is mainly used for river crabs to live and hide, and is also convenient for later fishing.

[0071] A 50cm high plastic escape-proof fence is installed around the rice fields to prevent river crabs from escaping and pests from entering.

[0072] 1. Experimental materials and experimental design:

[0073] The rice variety planted in the experimental rice fields is the mid-late maturing japonica rice "Nanjing 46", which is a long-cultivated mid-late rice variety in the middle and lower reaches of the Yangtze River. The crabs used in the experiment are the new variety "Shenjiang No. 1".

[0074] Water peanuts are laid in the middle of the crab pond for temporary rearing, and Hydrilla verticillata or water grasses are planted in the surrounding ditch. On May 8, 2023, the megalopa larvae were transported from the Sheyang nursery base to a small pond near the experimental field for centralized temporary rearing, with a stocking density of 6 catties / mu. Special feed for crab farming is fed, and fertilizer water is used to increase pond plankton as food.

[0075] Adjustments need to be made depending on the water level, water temperature and bait feeding conditions so that the breeding cycle is ≥45 days and the crabs grow to the size of sixth-stage crab larvae to avoid long breeding time and difficulty in connecting with the rice transplanting crop.

[0076] When the crabs are cultured to the sixth stage (about 45-60 days), select the all-female crabs with good vitality and healthy limbs and put them into the experimental rice fields. The stocking density is (2000 / mu) 30000 / hm 2 , high density (4000 / mu) 60000 / hm 2 The average stocking weight was (1.34±0.44)g. Figure 2 As shown, phase six is ​​easiest to identify.

[0077] The selection of stage 6 crab fry from the temporary pond needs to be done quickly, in a cool or shady area, to avoid high temperatures or direct sunlight that can affect the survival rate. At the same time, small amounts of crab fry should be caught from the temporary pond multiple times, and they should be placed in the rice field within 1 hour after selection, to prevent the crab fry from being out of water for too long, which may lead to an increase in the mortality rate of the crab fry after being put into the pond.

[0078] 2. Experimental rice field management:

[0079] In late May, water peanut and verticillium were planted at the bottom of the cross ditch in the experimental rice field. The ratio of water peanut to verticillium was 5:1. They were planted in boxes. The box planting area was 2m×2m in length and width. The spacing between boxes was 0.5-1m. 6-8 water plants were planted in each square planting area, and the spacing between each plant was ≥15cm. Compound fertilizer (150kg / hm 2 ) and then rotary tillage the soil.

[0080] Rice transplanting was carried out in early June, with a plant spacing of 16 cm and a row spacing of 30 cm. Rice was planted in blocks, with all rice seedlings planted except for the cross furrows. One row was planted every 10 meters, leaving a passageway for artificial feeding and crab activities. The rice plant spacing and row spacing between blocks were made as uniform as possible to facilitate ventilation between rice and the convenience of artificial feeding passages. In the daily management of rice, the use of highly toxic pesticides was prohibited to avoid affecting the growth and survival of crabs.

[0081] Two weeks after rice transplanting, the rice seedlings turn green, the water temperature reaches ≥18℃, and the rice seedlings are flooded with 30-40cm of water; the experimental juvenile crabs (female crabs in the sixth stage) are released into the ditch. When releasing, ensure that the aquatic plant coverage area is 50%-60% for the crabs to live and molt. The crabs are released in the cross ditch of the rice field to prevent the crabs from dying from stress on the rice field platform due to high temperature or being sunburned.

[0082] Use Hydrilla verticillata as an indicator of feeding. Female crab larvae feed on water peanuts and paddy field plankton and benthic organisms in the first 0-20 days of cultivation in rice fields. When the number of Hydrilla verticillata water plants decreases significantly, it means that the pond bait is insufficient and more feed needs to be added.

[0083] The next day, i.e., after the 21st day, compound feed (Huzhou Haihuang Biotechnology Co., Ltd., feed protein content of 38%) was fed; feeding was conducted once a day at 17:00, the feeding amount was about 2% of the crab body weight, and the feed specifications were increased from crushed feed to 2.5mm. A feeding table was placed on the experimental rice field platform to observe the feeding of young crabs, and the feeding amount was adjusted in time according to the water temperature and residual bait. The water quality was maintained in a suitable breeding environment (pH 7.0-9.0, dissolved oxygen concentration>3.00mg / L, ammonia nitrogen concentration<0.40mg / L, nitrite concentration<0.15mg / L).

[0084] The crabs were cultured in the rice fields until the end of September. After 70-80% of the first-year crabs were found to be sexually precocious through sampling, they were fed with feed for fattening. 100 crabs were sampled each time. The criteria for judging sexually precocious in the first-year crabs in the rice fields are: the belly button of the female completely covers the abdomen, and the belly button and carapace are relatively tilted. The male crabs are fully covered with large claw hairs, and the bottom of the belly button is obviously bulging, indicating maturity.

[0085] In late October, the first-year early-maturing crabs were caught using ground traps with 3 cm mesh. At the same time, taking advantage of the fact that the first-year early-maturing crabs crawled ashore in October, a rectangular pit with a length, width and height of 1×0.5×0.5 meters was dug near the cross ditch of the rice field. Plastic film was laid around the pit, and a light bulb was propped up on the top with a bamboo pole to lure the crabs into the trap for fishing. Figure 4 After the harvest, the fields were drained and dried, and the rice was harvested on November 20.

[0086] result:

[0087] 1. Growth and maturation patterns of juvenile crabs at different stocking densities

[0088] The effect of stocking density on the rate of early sexual maturity of the two species is shown in Table 1-1. During the test period from August 10 to 25, the young crabs in both density groups did not show early sexual maturity of the first age. Early sexual maturity of the first age crabs began to appear in the growth sampling on September 10. After sampling on September 25, the early sexual maturity rate of the first age crabs in both density groups reached more than 70%. The feed was continued to be fed and fattened until October 10, and it was found that the early sexual maturity rate of the first age crabs in both density groups had exceeded 90%. The sampling photos are shown in the figure below. Figure 3 , the weight of one-year-old precocious female crab exceeds 35g.

[0089] Table 1-1 Effects of two juvenile crab stocking densities on the precocious rate of first-year juvenile Chinese mitten crabs

[0090]

[0091] Effects of stocking density on the average body weight of female crabs at the one-year-old precocious crab and one-year-old juvenile crab stages Figure 5As shown in the figure, in the first two growth samplings, the average body weight of the one-year-old precocious crabs in the low-density group was lower than that in the high-density group. It was not until October 10 that the average body weight of the one-year-old precocious crabs in the low-density group was higher than that in the high-density group. Among them, there was a significant difference in the average body weight of the one-year-old precocious crabs in the two density groups on September 10 and October 10. The average body weight of females in the low-density group was always higher than that in the high-density group during the normal crab-holding stage. On September 25, the average body weight of the two density groups was significantly different (P<0.05). Note: The "*" in the bar graph indicates that there is a significant difference between different density groups at the same time (P<0.05), the same below.

[0092] As of October 25, the average weight of one-year-old precocious crabs and one-year-old juvenile crabs had no significant difference from that on October 10. Therefore, after the one-year-old precocious rate reached 70%, continue feeding for 20 days. When the one-year-old precocious rate exceeds 90%, they can be harvested.

[0093] The effects of different stocking densities on the gonadal index (GSI) and hepatopancreatic index (HSI) of one-year-old precocious female crabs are shown in Figure 6 As time went on, the GSI of the two density groups showed an upward trend. In terms of the difference between the groups, the GSI of the low-density group was always higher than that of the high-density group, while the HSI was the opposite.

[0094] 2. Rice and crab yield and size distribution under different density conditions

[0095] The effects of the stocking density of two juvenile crabs on the culture performance of river crabs and rice yield are shown in Table 1-2. In terms of rice yield, the rice yield of the high-density group was higher than that of the low-density group. In terms of river crab yield, the low-density group had advantages over the high-density group in terms of average body weight and per-acre yield, total yield, survival rate and feed conversion ratio of one-year-old precocious crabs. However, there was no significant difference between the two density groups in terms of average body weight and per-acre yield of normal crabs.

[0096] Table 1-2 Effects of two juvenile crab stocking densities on river crab culture performance and rice yield

[0097]

[0098] Effect of stocking density on final size distribution of one-year-old precocious crabs Figure 7 In terms of size distribution, the one-year-old precocious crabs in the low-density group were mainly distributed in the range of 30.00-44.99g and 50.00-54.99g, while the high-density group was mainly distributed in the range of 30.00-44.99g. Among them, the proportion of the low-density group in the range of 40.00-44.99g, 50.00-59.99g and >60g was higher than that in the high-density group. It can be seen that the low-density group has a clear advantage in the proportion of large sizes.

[0099] 3. Economic benefit evaluation

[0100] The economic benefits of the two stocking densities of juvenile crabs are shown in Table 1-3. Since the cost of the low-density group is less than that of the high-density group, the net profit and rate of return of the low-density group are higher than those of the high-density group when the total income is similar. The low-density group has advantages over the high-density group in terms of juvenile crab cost, feed cost, and income from one-year-old precocious crabs.

[0101] Table 1-3 Economic benefit analysis of two stocking densities of juvenile crabs (×10 3 Yuan / hm 2 )

[0102]

[0103] In summary, the present method can achieve a ratio of one-year-old precocious crabs in rice fields of more than 90% under two stocking density conditions of less than 5,000 crabs per mu, and the yield of one-year-old precocious crabs per mu is about 40 kg, with an average one-year-old precocious crab size of ≥35 g per crab. A small amount of normal crabs can also be harvested for breeding in the next year.

[0104] Example 2

[0105] In 2023, the inventor screened the optimal density of one-year-old precocious crabs in rice fields at the Xuancheng Rice-Fish Breeding Research Base of Shanghai Ocean University. On May 11, 2023, large-eyed juveniles were placed in a 10-mu crab temporary rearing pond at a weight of 6 jin / mu for temporary rearing.

[0106] 1. Preparation for Isolation

[0107] There are 4 experimental ponds (C1, C2, C3, C4), each with an independent water inlet and outlet system. Six experimental enclosures were set up in each of the 4 ponds, each with a size of 5×8m. The crab density gradient was set to: 0 crabs / m 2 , 3 pieces / m 2 , 6 pieces / m 2 , 9 pieces / m 2 , 12 pieces / m 2 , 15 pieces / m 2 . 20cm double-sided plastic plates are sewn on the upper edge of the enclosure to prevent the test crabs from escaping and external organisms from entering the test enclosure. The enclosure is fixed with galvanized pipes on all sides and fixed with ground nails every 30cm on the lower edge to prevent the test crabs from escaping. A cross-shaped middle ditch with a width of 0.3m and a depth of 0.5m is dug in the center of the enclosure. Water peanuts and a small amount of verticillaster hydrilla are planted in the ditch (6-8 water plants are planted in each square planting area). The ratio of the two is about 10:1, which is convenient for river crabs to molt and avoid high temperatures and enemies.

[0108] 2. Rice Planting

[0109] On June 25, the rice seedlings (plant height 20 cm) were transplanted into the experimental enclosure. The rice planting and the planting of waterweed in the ditch were both carried out using the methods listed in the patent of this invention. The rice plant spacing was ≥16 cm, the row spacing was ≥30 cm, and the rice was planted in blocks, except for the cross ditch. On July 10, female crabs (sixth stage) with sound appendages, uniform size, clear vision and good vitality were selected for stocking. The initial weight of all female crabs was (1.38±0.29) g.

[0110] The entire experiment started with planting aquatic plants on July 5 and ended on November 15, a total of 133 days.

[0111] No feed was given to the female crabs for the first 20 days after they were released. Starting from the 21st day, Chinese mitten crab compound feed (produced by Zhejiang Aohua Feed Co., Ltd.) was fed at around 16:30 every afternoon. The feeding amount was 1-3% of the total amount of juvenile crabs in the enclosures. One feeding table was placed in each enclosure. The daily feeding amount was flexibly adjusted according to the weather, water temperature and feeding conditions on the feeding tables and recorded in time. Water peanuts and verticillium hydrillae in the middle ditch were combed in time, and the water grasses were always kept covering about 40% of the middle ditch area to prevent them from being too dense and affecting the normal growth and activity of juvenile crabs; the water quality was tested regularly every week using the simple test kit of Nanhua Qianmu Biotechnology Co., Ltd. to maintain the water quality in a suitable breeding environment (pH 7.0-9.0, dissolved oxygen concentration>3.00mg / L, ammonia nitrogen concentration<0.40mg / L, nitrite concentration<0.15mg / L).

[0112] (III) Harvesting of one-year-old precocious crabs and snapper crabs and harvesting rice

[0113] From October to November, ground traps were used to catch one-year-old precocious crabs. After all the crabs were caught, the water level was lowered until the pond surface was completely exposed. Around November 10, rice was harvested manually and the yield was measured. The fishing was mainly carried out using ground traps with 3 cm mesh. The water level was gradually lowered to force the remaining young crabs into the cross ditch, and ground traps were used to continue fishing in the ditch.

[0114] Weight measurement of juvenile crabs in rice fields: After crab seedlings are released, they are weighed every 15 days or so under normal feeding conditions. 20 crabs are randomly sampled from each pond and the average weight is calculated. At the final harvest, all juvenile crabs are drained and captured for counting and weighing to calculate the average size and yield.

[0115] 3. Results

[0116] 3.1 Effects of different stocking densities on rice

[0117] As shown in Table 3-1, the stocking density of river crabs had no significant effect on the number of grains per ear and 1000-grain weight, while the number of effective tillers, fruiting rate and yield gradually increased with the increase of stocking density. The stocking density of river crabs had no significant effect on the growth height of rice plants ( Figure 8 )

[0118] Table 3-1 Effects of different crab stocking densities on rice yield evaluation indicators

[0119]

[0120] 3.2 Effects of different stocking densities on juvenile crabs

[0121] As shown in Table 3-2, the lower the stocking density, the higher the early maturity rate. On October 10, when sampling, it was found that the density was less than 6 pieces / m -2 The precocious rate of young crabs in the group was ≥77.71%; on November 10, the density was less than 6 crabs / m -2 The precocious rate of young crabs in the group was ≥91.83%, and more than 9 crabs / m -2 The precocious rate of young crabs in the group showed a downward trend. The effects of different stocking densities on the final culture performance of river crabs are shown in Table 3-3. The yield of normal crabs showed an upward trend with the increase of stocking density, but the yield of early-maturing crabs showed an overall trend of first increasing and then decreasing. -2 The yield and total yield of early-maturing crabs in the group with the highest yield were the highest, but the feed conversion ratio was the lowest. The weight of early-maturing crabs decreased with the increase of stocking density, and the density was ≤6 crabs / m -2 The average size of early-maturing crabs in the group was ≥39.80±1.58g.

[0122] Table 3-2 Effect of stocking density on the precocious rate of juvenile crabs during breeding

[0123]

[0124] Table 3-3 Effects of different stocking densities on the final culture performance of river crabs

[0125]

[0126] In summary, the stocking density of young river crabs should be ≤ 6 per cubic meter. -2 The precocious rate of young crabs in the group was ≥91.83%, 6 crabs·m -2 The early-maturing crab yield and total yield of group A were the highest, but the feed conversion rate was the lowest, and the density was ≤6 crabs·m -2 The average size of the early-maturing crabs in the group was ≥39.80±1.58g. It can be seen that by applying the method of the present invention, large-sized one-year-old early-maturing juvenile crabs can be obtained, with a one-year-old early-maturing rate of ≥91.83% and a large average size (≥39.80±1.58g).

[0127] Example 3

[0128] In order to compare the effects of different aquatic plants planted in the cross-shaped ditches of rice fields on the breeding effect and bait contribution of one-year-old precocious crabs, the inventors conducted an experiment of planting four types of aquatic plants in the cross-shaped ditches of rice fields at the Xuancheng Rice-Fish Breeding Research Base of Shanghai Ocean University.

[0129] A total of 9 paddy fields were used for the experiment, each with an area of ​​40 square meters (length × width = 8 meters × 5 meters). A cross ditch was dug in the middle of the paddy field, 1 meter wide and 0.5 meter deep. Each paddy field was separated by a ridge, and the water inlet and outlet were independent. Plastic escape prevention panels were set around each paddy field, the same as in Example 1.

[0130] On June 5, 46 varieties of rice were planted in Nangeng. The experiment was divided into 4 groups. On June 8, Hydrilla verticillata and Alternanthera philoxeroides were planted in the cross ditch, and peanuts were added. The ratio of Hydrilla verticillata or Alternanthera philoxeroides to peanuts was 1:5. Duckweed was laid in the ditch of another group. After planting, 21 kg of slow-release compound fertilizer (nitrogen, phosphorus and potassium content were 16% respectively) was applied per mu of ditch area. Three rice fields were set up for each waterweed group. On June 24, large-sized bean crabs were released at a density of 4,500 per mu. After release, routine management was carried out, and samples were weighed every 30 days. At the same time, crab seedlings, feed, zooplankton, phytoplankton, waterweed, sediments and benthic organisms were collected for stable isotope analysis; at the end of the experiment, one-year-old precocious crabs were collected for stable isotope analysis. On November 10, drainage began to catch one-year-old precocious crabs with ground traps, and the yield and survival rate were counted.

[0131] Isotope sampling of juvenile crab muscle and its main food source. Sample collection began one month after the experiment officially began, when rice and juvenile crabs grew and the pond environment became stable. The specific sampling method was referred to the method of Li Cong et al. (2018) (Table 2-1). Due to the small body mass of juvenile crabs, muscle samples of juvenile crabs were sampled by mixing multiple individual samples, and all samples were stored in a -20℃ refrigerator for future use. Isotope-related data were measured by the Analysis and Testing Center of Shanghai Jiaotong University. Each group collected 1 portion of aquatic plants, 1 portion of zooplankton, 1 portion of phytoplankton, 1 portion of benthic organisms, and 1 portion of different feeds. There were 3 crabs in each enclosure.

[0132] Tab.2-1Sample collection and pretreatment

[0133]

[0134]

[0135] The effects of different stocking densities on the composition and contribution rate of juvenile crab feed are shown in Fig. 9 The method of the present invention found that artificial feed only accounted for 9.72%-10.49% of the total food of juvenile crabs, and benthic organisms were the first food source for juvenile crabs in each density group, accounting for 12.15%-14.70%, and the proportion of benthic organisms increased with the decrease of density. Among the planted aquatic plants, the food contribution rate of Hydrilla verticillata was the highest, followed by Duckweed, and Alternanthera philoxeroides was the lowest. The contribution rate of Hydrilla verticillata was 3 crabs / m -2Group and 6 m -2 The rice biofilm, as a unique food source in the rice field environment, accounts for 10.21%-12.37% of the food of young crabs, and the proportion of food increases with the increase in density. Sediments account for 10.82%-11.37%, and background crabs account for 8.04%-9.04%. The smallest proportions are zooplankton and phytoplankton, which are 8.92%-10.19% and 5.71%-7.03%, respectively.

[0136] It can be seen that by using the method of the present invention, the density is lower than 6 pieces / m -2 When planting Hydrilla verticillata, the food contribution rate of juvenile crabs in rice fields is the highest, which is beneficial to reduce the feed coefficient and save costs. This density range is within the constraint range of the patent of this invention, and this aquatic plant is the optimal aquatic plant recommended by the patent of this invention.

[0137] The above describes the specific embodiments of the present invention. It should be understood that the present invention is not limited to the above specific embodiments, and those skilled in the art can make various changes or modifications within the scope of the claims, which does not affect the essential content of the present invention. In the absence of conflict, the embodiments of the present application and the features in the embodiments can be combined with each other arbitrarily. All prior arts that do not contradict the scheme of the present invention, including but not limited to prior patent documents, prior public publications, prior public uses, etc., can be included in the protection scope of the present invention.

[0138] In addition, the combination of the various technical features in this case is not limited to the combination described in the claims of this case or the combination described in the specific embodiments. All technical features recorded in this case can be freely combined or combined in any way unless there is a contradiction between them.

Claims

1. A method for breeding one-year-old precocious female crabs in rice fields in East China, characterized in that: The following steps are involved: (1) Dig a cross-shaped trench in the middle of the rice field and plant the following aquatic plants in the trench: (a) Water Peanuts and / or Bighead Carrots, and, (b) Elodea and / or Hydrilla verticillata; (2) Transplanting rice seedlings into rice fields; (3) When the rice seedlings turn green and the water temperature is ≥18°C, healthy female crab larvae are placed in the cross grooves of the rice fields; (4) After the female crabs have been cultured in the rice field for 15-20 days, they are fed with crab culture feed; (5) After the one-year sexual precocity rate reaches ≥70%, continue to feed and fatten the crabs, and start catching the one-year sexual precocious female crabs after 20 days; There is no restriction on the order of steps (1) and (2).

2. The method for breeding one-year-old precocious female crabs in rice fields in East China according to claim 1, characterized in that: In step (1), the crablets develop to stage six or above.

3. The method for breeding one-year-old precocious female crabs in rice fields in East China according to claim 1, characterized in that: The average size of the crablets is ≥1g / piece, and the stocking density is ≤75,000 / hm2. 2 .

4. The method for breeding one-year-old precocious female crabs in rice fields in East China according to claim 1, characterized in that: In step (2), when the crab fry are released, the aquatic grass coverage area is 35%-70% of the cross ditch area, the water level in the cross ditch of the rice field is ≤1 meter during the breeding period, and the water level of the rice planting platform is maintained at 20-40cm.

5. The method for breeding one-year-old precocious female crabs in rice fields in East China according to claim 1, characterized in that: In step (1), the cross groove is 0.3-4 m wide and 0.3-0.8 m deep, and the total area of ​​the cross groove accounts for ≤10% of the total rice field area; The water plants are planted in boxes, with the spacing between different planting boxes being 0.5-1 meter. 6-8 water plants are planted in each square meter of planting area, with the spacing between each plant being ≥15 cm.

6. The method for breeding one-year-old precocious female crabs in rice fields in East China according to claim 1, characterized in that: During the breeding cycle, the water level from the bottom of the cross ditch to the water surface is ≤1 meter, and the water level in the rice planting part is maintained at 20-40cm.

7. The method for breeding one-year-old precocious female crabs in rice fields in East China according to claim 1, characterized in that: In step (1), the planting ratio of aquatic plants (a) and (b) is 3-20:

1.

8. The method for breeding one-year-old precocious female crabs in rice fields in East China according to claim 1, characterized in that: In step (4), whether the amount of Elodea and / or Hydrilla verticillata decreases is used as an indicator feature for whether to start feeding the compound feed.

9. The method for breeding one-year-old precocious female crabs in rice fields in East China according to claim 1, characterized in that: The method for obtaining female crab larvae is to release megalopause larvae into crab breeding ponds at a weight of ≤7 jin per mu, and temporarily raise them for 45-60 days. When they develop to at least the sixth stage of crab larvae, healthy females are selected and released into the ditches of rice fields.

10. The method for breeding one-year-old precocious female crabs in rice fields in East China according to claim 1, characterized in that: In step (5), after the one-year-old precocious female crabs are caught, the rice is harvested.

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