Key Technical Points for Stocking Seed Stock in Rice-Field Farming of Red Swamp Crayfish

There are several stocking methods for farming red swamp crayfish in rice fields

1. After rice transplanting, from June to early July, when the seedlings turn green and begin tillering, release juvenile crayfish, and the rice and crayfish grow together for a period. After the rice is harvested, some crayfish that have not reached market size and selected broodstock are kept in the field for continued farming until May to June of the following year, when all are harvested. This juvenile crayfish stocking model is divided into two farming stages, one before and one after. The first stage is July, August and September, and the second stage is from October to May and June of the following year. In the first stage, besides farming some adult crayfish for market, the main purpose is to lay a solid foundation for the second stage of farming, ensuring that after rice harvest, 10-15 kg (1200-1500 individuals) of juvenile crayfish are retained per mu, and about 50 broodstock crayfish are retained per mu, of which more than 40 are females. After the retained juvenile crayfish and the reproduced fry are farmed through one winter and one spring, the yield can reach 120-150 kg.

2. After mid-August, release broodstock and egg-bearing crayfish into the ring ditch. After the rice is harvested, raise the water level in the rice field to 50-60 cm, and farm until May-June of the following year, then harvest. With this stocking method, note the following: 1. The stocking amount must not be too large; generally keep it at about 5-10 kg per mu, with a female-to-male ratio of 4-5:1. As time goes on, the female-to-male ratio gradually increases. In September, the female-to-male ratio can be 7-8:1. By early October, most of the collected broodstock are already in a pre-spawning state, so males need not be released. 2. When purchasing broodstock, they must be carefully selected; as far as possible choose broodstock with strong vitality, large individuals, good maturity, purple heads and red tails. 3. Improving the survival rate of broodstock is the key to obtaining fry. Broodstock must be purchased locally; to take inbreeding into account, female crayfish should be purchased from different locations.

3. Before rice transplanting, in April-May, release juvenile crayfish into the ring ditch, with a small ridge left between the ring ditch and the rice field for relative isolation. In mid-June, after the rice turns green and begins tillering, increase the water level so that the rice field and the ring ditch become one. Start rotational harvesting in July, select and retain broodstock after August 10, and after the rice is harvested, harvest and clear the pond. This method mainly refers to having completed all preparatory work in winter and spring; rice transplanting is mainly spring rice, generally completed around May 20. This method is beneficial both to high and efficient rice yields and to crayfish farming. On this basis, three points should be noted.

The first point is: doing a good job of the rice-field farming engineering is the primary condition for farming crayfish in rice fields. Carry out renovations according to the requirements for field engineering construction. It should be explained that the ring ditch in the field should be dug 0.5-1 m away from the field ridge, which is conducive to rice-crayfish production operations and avoids collapse. The ditch is 2 m wide and 0.8 m deep. The fry breeding ditch is 6 m wide and 0.8 m deep. In the middle of the breeding ditch, a fry collection pond is left; the pond is 0.2 m deeper than the breeding ditch, with a working ridge 1 m wide at the top between them, to facilitate crayfish burrowing and operation. When the field plot exceeds 15 mu, dig "+" or "#" shaped field ditches in the field, 1 m wide and about 0.5 m deep. When setting up anti-escape nets, use two layers of anti-escape netting. The first layer is close to the water edge to prevent crayfish from burrowing, and the second layer is used for anti-escape purposes.

The second point is: timely pond clearing and timely planting of aquatic plants are key measures for farming crayfish in rice fields. In crayfish farming, emphasizing timely pond clearing is an effective measure for raising healthy crayfish and large crayfish. In particular, ponds with rice-crayfish rotation that must be farmed every other year should be cleared. Pond clearing not only removes wild trash fish, harmful organisms and some aquatic plants that cannot be used by crayfish in the rice field, but also effectively controls the crayfish stocking amount. The chemicals generally used for pond clearing are quicklime, chlorine dioxide, etc. As for the timing of pond clearing: first, in October after the rice is harvested; this pond clearing should clean both the ring ditch and the harvested rice field. Second, in May-June of the following year; this pond clearing mainly cleans the ring ditch. Third, during the entire farming process of this period (June, July to June, July of the following year), there should be one or two small pond clearings, namely appropriately cleaning the prepared broodstock breeding ditch in early August, and also cleaning the ring ditch when the rice field is dried in the later stage of rice growth. The above pond clearings should adopt different methods and means according to different situations.

There are five kinds of aquatic plants suitable for planting in crayfish ponds: Hydrilla verticillata, Elodea, alligator weed, duckweed and water hyacinth. Among them, Hydrilla verticillata and Elodea are the main planting targets, alligator weed and duckweed are companion varieties, and water hyacinth can only be used as an auxiliary measure. As for the planting area, the aquatic plant coverage rate in the crayfish pond should be controlled within 2/3 of the total area. During the farming period, if the aquatic plants are eaten by crayfish, they should be replenished in a timely manner; if there are too many, they should be removed in a timely manner. Elodea is planted in winter and spring; the cultivation method of Hydrilla verticillata is basically the same as that of Elodea; alligator weed and duckweed can be scooped up as plants and moved into the crayfish pond at any time.

The third point is: rational stocking and rotational harvesting and stocking are effective means of increasing the yield of crayfish farming in rice fields. The juvenile crayfish released in June and early July are not necessarily uniform in size; as long as they have not reached market size, they can all be released. Release the juvenile crayfish 15-20 days after rice transplanting, with a stocking amount of about 30 kg per mu. Release about 10 kg the first time and observe for a few days before releasing the second batch. The source of juvenile crayfish is best from local purchases, releasing as soon as they are purchased, and shortening the purchase and release time as much as possible to improve the survival rate of juvenile crayfish. When releasing juvenile crayfish, they should be evenly distributed throughout the field plot: one third released into the ring ditch and two thirds released into the rice field. Crayfish released directly into the rice field will not harm the seedlings or affect the growth of the rice; at this time, the aquatic plants they eat are only the young shoots of weeds that have just emerged in the rice field. Because crayfish have a strong sense of territory, only even distribution and release can effectively use the shallow-water environment of the rice field. In crayfish farming, rotational harvesting and stocking must be carried out in a timely manner according to growth conditions. Juvenile crayfish released in mid-June can begin to be harvested in mid-July, and according to the harvesting situation, crayfish fry can also be appropriately supplemented.

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