Introduction to the characteristics of crayfish

1 Characteristics of Crayfish

Crayfish (Procambarus clarkii), also known as Procambarus clarkii, red crayfish and freshwater crayfish, has a hard, dark red shell, and the carapace is nearly Black, with a wedge-shaped stripe on the back of the abdomen. The adult body is 5.7~11.8 cm long. There are 3 pairs of tentacles on the head and 5 pairs of walking legs on the chest. The ends of the 1st to 3rd pair of walking legs are in the shape of pincers, and the ends of the 4th and 5th pair of walking legs are in the shape of pincers. Claw-like, the second pair of legs is particularly developed and becomes a very large chela. Crayfish grow quickly and have strong adaptability. The suitable water temperature is 10~30 ℃. The whole development process is divided into 4 stages: larvae, juvenile shrimp, adult, and adult shrimp. The larvae feed on food brought by the yolk or the mother's breathing water; the larvae live independently and mainly feed on zooplankton, with a body length of 1.0~3.0 cm; the adults are immature individuals, actively feeding on zooplankton and water insect bait, with a body length of more than 3.0 cm ; Adult shrimp are broodstock and commercial shrimp with mature gonads.

2 Ecological cultivation technology of crayfish rice fields

2.1 Construction of rice field facilities

Choose sites with low terrain, good water retention, far away from pollution sources, sufficient water sources, and convenient drainage and irrigation Rice fields to ensure that they are not flooded (from June 19 to 21, 2019, crayfish farmers in Meishan Town and Baitafan Town, Jinzhai County were affected by heavy rains and floods, and crayfish escaped in large numbers, causing economic losses of 120,000 yuan); area 0.67~3.33 hm 2 . Widen, heighten, and reinforce the field ridges to make them more than 0.8 m above the field surface, with a ridge width of 5 to 6 m and a top width of 2 to 3 m. Excavate along the inside of the rice field ridges to a width of 3.5 to 4.0 m and a width of 1.0 to 1.5 m. Deep circular ditches for rice fields. For fields with an area of ??3.33 hm 2 or more, a "cross"-shaped trench with a width of 1~2 m and a depth of 0.8 m should be dug in the middle.

2.2 Preparation for stocking

2.2.1 Transplanting aquatic plants. Planting aquatic plants accounts for about 30% of the paddy field area (50% of the ditch area), mainly including Elodea, Hydrilla verticillata, Eichhornia crassipes, and water hyacinth. The appropriate planting time is mid-to-late November, and the use of amino acid-containing , humic acid, bio-organic fertilizer with various trace elements.

2.2.2 Apply sufficient base fertilizer. Apply special biological fertilizer for rice. Seedlings are generally transplanted in early or mid-June, with 750 kg/hm 2 of biological rice-specific fertilizer as base fertilizer, 75 kg/hm 2 of urea as tiller fertilizer, and 75 kg/hm 2 of potassium fertilizer as ear fertilizer; avoid using ammonia and carbonic acid. Ammonium hydrogen. After the rice is harvested, apply a commercial straw decomposition agent of 30 kg/hm 2. After decomposition, it can not only fertilize the field, but also be used as crayfish bait. In winter, apply bio-organic fertilizer 750~1 500 kg/hm 2 or put in 60~75 bags/hm 2 of dry chicken manure, and spread it flatly in the rice field without opening the bags.

2.2.3 Rice field disinfection. After the rice field transformation is completed, the ditch must be disinfected in the first year, using 1 800-2 250 kg/hm 2 of quicklime with water to kill harmful organisms and pathogenic bacteria; when there are shrimps in the ditch, two Chlorine oxide for disinfection.

2.3 Stocking

2.3.1 Selection of shrimp seedlings. It is best to choose young shrimps cultured in surrounding rice fields or collected from ponds and ditches as shrimp seedlings. They should be dark red or deep red in color, shiny, with a smooth body surface and no attachments; the individuals should be uniform in size, complete in appendages, strong in physique, and capable of mobility. powerful.

2.3.2 Transportation of shrimp larvae. For long-distance transportation of shrimp seedlings, high-quality juvenile shrimps should be selected and packed into plastic shrimp baskets. The weight of each basket should not exceed 5 kg. After loading, a layer of moist aquatic plants should be placed on top. The transportation time should not exceed 2 hours; the transportation time of live water trucks should be 2 to 10 hours. between; nylon bags filled with water and oxygenated for transportation can guarantee more than 10 hours.

2.3.3 Release of shrimp seedlings. From May to June every year, about 150,000 juvenile shrimps/hm 2 with a size of 40 to 60 shrimp/kg (equivalent to 3 to 4 cm) are released into the rice fields; if juvenile shrimps are released after the mid-season rice harvest from September to October, 4 Adult shrimps are harvested from late September to May, and 225,000 juvenile shrimps with a size of 2 to 3 cm are released at the same time/hm 2 . When placing, immerse the shrimp basket in the water repeatedly 2 to 3 times, 1 to 2 minutes each time, to allow the shrimp seedlings to adapt to the water temperature, and then place them in ditches or field ditches.

2.4 Scientific planting

2.4.1 Rice cultivation. Shrimp farming rice fields generally only grow mid-season rice, and use dry-breeding and dry-tube cultivation. They choose tight-eared varieties that are water-saving, have small leaf opening angles, are resistant to diseases and insect pests, are resistant to lodging, and have strong fertilizer tolerance. The rice fields are drained and prepared from April to May; rice seedlings are transplanted in shallow water in early June and planted with wide rows and dense plants, that is, the row spacing is 25~40 cm and the plant spacing is 18 cm; the rice is harvested in mid-August to September. Plant rice scientifically and spray no or less pesticides throughout the season to reduce pesticide residues in rice and make the rice taste better and ensure quality. Crayfish have certain requirements for water quality. If the water quality is damaged, crayfish will act as an early warning. Rice yield can reach 9.0~10.5 t/hm 2 .

2.4.2 Feeding. After the shrimp larvae are released, a large number of zooplankton are cultivated, which can provide good food for the young shrimps. Increase feeding from July to August, such as vegetable cakes, bean dregs, screw meat, mussel meat, lettuce leaves, rye grass, etc. Try to achieve a reasonable mix of animal, plant and green feed to ensure balanced nutrition. The feeding amount is 1% of the total weight of the shrimp seedlings. Artificial feed is fed once every day in the evening, and the feeding amount is 1% to 4% of the weight of shrimps in the rice field.

2.5 Daily management

2.5.1 Molting management. Strengthen the management of crayfish during the molting period. It is strictly forbidden to interfere with large numbers of crayfish when they molt. Feed high-quality and delicious feed immediately after molting to prevent each other from killing each other.

2.5.2 Rice field management. From July to September, except for the drying period, the water level in rice fields should be controlled at about 20 cm. Dry the field 15 to 20 days after transplanting. It is recommended to dry the field lightly until the field does not sink and there are no cracks on the field surface. After the field drying is completed, the original water level should be restored in time to avoid adverse effects caused by excessive density of crayfish in the ditch for a long time.

2.5.3 Water level management. After the rice is harvested, the water in the rice fields should be slowly deepened to avoid rapid deterioration of water quality caused by one-time flooding of rice straw and chicken manure. From October to December, the shallow water level of Baotian surface is 10~20 cm; from December to February of the following year, the deep water level is maintained at 30~50 cm; from March to April, the shallow water level is maintained at 10~20 cm; from April to May, the water level is maintained at 30~ A deep water level of 50 cm; water level management should be carried out according to rice cultivation requirements from June to September.

2.5.4 Water quality management and daily inspections. The optimum pH value of water is about 8, so quicklime should be regularly used to adjust it. The general dosage is 75.0~112.5 kg/hm 2, and it should be splashed regularly every month. Establish an inspection system, insist on inspecting fields every day, and take timely measures if abnormalities are found.

2.6 Prevent diseases and eliminate pests

The natural enemies of crayfish include fish such as carp, crucian carp, snakehead, and catfish; reptiles such as turtles and soft-shell turtles; land animals such as water rats, water snakes, and wild cats. Animals; birds such as herons and kingfishers. Sprinkle quicklime 1 125 kg/hm 2 before stocking to remove harmful organisms. Use a 20-mesh gauze to filter the water. At the same time, some colored strips and scarecrows can be set up on the edge of the field to scare and drive away water birds. For moss, use quicklime to turn into a slurry and sprinkle it evenly while it is hot. Use 300 kg/hm 2 at a water depth of 1 m. After 3 days, use Green Shrimp 75 kg/hm 2 to cultivate algae to prevent the moss from rebounding. For cyanobacteria, dilute 500 mL of Jianshuibao into a 100-200 times solution and splash it evenly 1-2 times with an interval of 10-15 days between each time.

2.7 Adult shrimp fishing

2.7.1 Rotate catch and release. The crayfish rice field breeding period is about 60 days from larvae to adults, about 45 days from juvenile shrimps to adults, and they can be fished after 30 days of stocking. Crayfish fishing uses ground cage nets, hand nets, and can also be fished in dry field water. After the first harvest is completed, 15,000 to 45,000 juvenile shrimps/hm 2 with a size of 3 to 4 cm will be released according to the remaining juvenile shrimps in the rice fields.

2.7.2 Reserve broodstock. In order to meet the demand for shrimp seeds for shrimp farming in rice fields, in the early stage of adult shrimp fishing from August to September, "catch the big ones and leave the small ones", and in the later stage, "catch the small ones and leave the big ones" until the size of the caught shrimps drops to less than 0.4 kg/head, that is, The purpose of stopping fishing is to retain enough broodstock for breeding in the following year, with an average of no less than 225~300 kg/hm 2.