Key Points and Detailed Methods for Crayfish Fry Breeding Technology

In crayfish farming, fry breeding is a key point. Although crayfish can mate almost year-round, the peak is in spring each year. Mating generally takes place in open areas of the water, and the mating water temperature range is wide, from 15°C to 31°C. Reproduction is quite special, with most of the process completed in burrows, so egg-bearing crayfish are rarely seen in ordinary production. Therefore, attention should be paid to strengthening management.

Selection of Parent Crayfish

Parent crayfish can be selected from March to October of the same year, requiring a body weight of 20-25 grams, complete appendages, good health and no disease, and strong activity. The male-to-female ratio is 1:1 (based on actual farming experience). Male and female crayfish have obvious features in appearance and are easy to distinguish. In sexually mature crayfish, males are noticeably larger than females; males have thick and large crayfish legs, with a bright red soft wart on the outer side of both ends of the legs, while females are pale even if colored. The male genital pore opens at the base of the 5th pair of walking legs, while the female genital pore opens at the base of the 3rd pair of walking legs. Sexually mature female crayfish have a swollen abdomen, while the abdomen of male crayfish is relatively narrow.

Parent Crayfish Breeding

1. Pond construction: The area of the parent crayfish pond should be about 2-5 mu, the bottom soil should preferably be loam, the water depth should be more than 1-1.5 m, and there should be sufficient and good water sources. Water inlet and outlet should be built well. The pond ridges around should be built with plastic film or calcium-plastic boards to create an anti-escape wall. 7-10 days before stocking, the pond should be disinfected with 50-80 kg/mu quicklime in a drained pond. After disinfection, water should be added after filtration (to prevent wild miscellaneous fish from entering the pond), and then decomposed livestock and poultry manure should be applied at 100-200 kg/mu to fertilize the water quality. Hidden objects for crayfish to climb and rest on, such as branches, tree roots, and bamboo tubes, should be placed in the pond, and some aquatic plants should be transplanted.

2. Stocking of parent crayfish: Parent crayfish ponds can be stocked with 40-60 kg/mu of parent crayfish. Before stocking, soak them in 3% salt water for 10 minutes to kill pathogens. To make full use of the water body and regulate water quality, silver carp and bighead carp can also be polycultured at 50-100 fish/mu. During the breeding period, fresh aquatic plants, soybean cake, wheat bran, or compound feed can be fed, and a portion of animal-based feed should be added, such as chopped snail and mussel meat, and livestock and poultry slaughtering scraps.

3. Daily feeding amount: Generally, in March it is 2-3% of the parent crayfish body weight, in April 4-5%, and after May 6-8%. Feed once each morning and evening every day, mainly in the evening, accounting for 70% of the daily feed amount. At the same time, strengthen water quality management, replace with new water once every 10-15 days, replacing 1/3 each time, and splash quicklime mixed with water once every 20 days at 5-10 kg/mu to increase soil calcium, maintain good water quality, and promote gonadal development of parent crayfish.

Crayfish Reproduction and Overwintering

1. Parent crayfish reproduction: Usually in April-May, when the water temperature is above 20°C, parent crayfish begin to mate. Fertilized eggs hatch into fry in the female crayfish's abdomen, and hatching takes 40-70 days. After hatching, the fry complete the growth and development process of the juvenile stage under the protection of the mother. Once the fry leave the mother, they can actively feed and live independently. When a large number of fry appear in the breeding pond, seedlings should be collected in time for fry breeding.

2. Parent crayfish overwintering: The minimum survival water temperature for crayfish is 5°C. When the water temperature is below 0°C, crayfish about 3 cm long have a very high mortality rate during overwintering. Although adult crayfish can survive, large numbers will also die after 2-3 months. Therefore, raising the water level, doing a good job in parent crayfish overwintering, and ensuring the water temperature during overwintering are also important parts of the entire breeding work.

Crayfish Seedling Technology

The egg-bearing capacity of crayfish is generally 200-800 eggs, the fertilization rate can be above 98%, and the hatching rate can reach 80-85%. The problem is that after emergence, the juvenile shrimp grow and molt frequently and are highly susceptible to environmental conditions, which affects the seedling rate. To improve the seedling rate, the key is to do the following well:

1. Water quality requirements: During crayfish breeding, the water body should remain relatively stable, the water quality should be fresh, the pH value should be between 6.5-8, large day-night water temperature differences should be prevented, and dissolved oxygen in the water should be maintained above 5.6 mg/L.

2. Water body environment: There must be aquatic plants on the water surface and at the bottom, such as water hyacinth, alligator weed, green algae, and Hydrilla verticillata, accounting for 1/3, and there should be hidden burrows to increase attachment sites for shrimp fry molting. It is also convenient to wash seedlings with water hyacinth to check and grasp the emergence time and shrimp growth conditions. Add fences and filter nets at the water inlet to prevent harmful organisms from entering the pond, and at the same time prevent frogs from entering the pond to lay eggs and avoid tadpoles eating shrimp fry. At the same time, prevent parent crayfish from climbing and escaping.

3. Strengthen inspection: Persist in checking emergence conditions in the morning and evening. When juvenile shrimp leave the mother, promptly catch the parent crayfish and return them to the parent crayfish pond for re-cultivation. Minimize counting and transferring between ponds, and handle operations with special care to avoid affecting parent crayfish that are bearing eggs or have just hatched shrimp.

4. Ensure feed supply: Timely cultivate small zooplankton such as rotifers for the newly hatched juvenile shrimp to feed on. An estimated 3-5 days before emergence, begin catching a small amount of small zooplankton from the dedicated hatching pond into the shrimp fry pond. Also use cooked egg yolk, soybean milk, and other materials to promptly supplement the food supply needed by juvenile and young shrimp.