Breeding Techniques of Early Breeding of Carp in Cold Region
In the Ningxia region, naturally reared fry larvae typically become available in mid to late May. However, this timing results in smaller fish size and lower survival rates during winter. To address this issue, local squid producers have traditionally imported fry from southern Wuzi using air transport. While this method improves availability, it is expensive and increases the risk of introducing pathogens. In 2004, the author conducted an artificial breeding experiment in March and April to achieve earlier fry release, aiming to boost production and income.
**Materials and Methods**
1. **Broodstock Breeding and Selection**
- **Cultivation Ponds**: The ponds covered 8 acres, all rectangular plastic greenhouses oriented east-west. The bottom sludge was 10–15 cm deep, with a water depth of 1.2 meters. Before stocking, dry lime was used for cleaning at a rate of 100–150 kg per mu.
- **Broodstock Source**: Sturgeon aged 2–8 years, weighing 1.0–4.0 kg, were selected. A total of 875 individuals were used, including 575 females and 300 males.
- **Feeding and Management**: Stocking density was 50–80 per mu, with feeding occurring 1–2 times daily at 5%–10% of body weight. After 30 days, gonads developed well.
- **Broodstock Selection**: Fish weighing 1–3 kg with no injuries, smooth skin, and normal behavior were chosen. Females had soft, swollen bellies, while males had significantly smaller abdomens.
2. **Artificial Oxytocin and Incubation**
- **Oxytocin Production**: A standard cement pool (3.8m x 3.1m x 1.2m) was used with Yellow River water. Oxygen was increased via aeration, and temperature was maintained at 22–26°C.
- **Injections**: A combination of DOM+LRH-A2 was injected into the body cavity (3 mg DOM + 10 μg LRH-A2 per kg female; half dose for males). The needle was inserted at a 45–60° angle, avoiding internal organs.
- **Artificial Insemination**: Dry insemination was used. Eggs were collected by gently squeezing the abdomen, then mixed with male sperm for fertilization.
- **Incubation**: Fertilized eggs were placed in muddy water to stick, then washed and treated with methylene blue before hatching in running water. About 800,000 eggs per cubic meter were hatched.
3. **Artificial Seedling Cultivation**
- **Pre-cultivation**: Ponds were prepared with quicklime and fermented manure. Water was added gradually, and stocking density was set at 120,000–150,000 per mu.
- **Incubation Period**: Fry hatched after 5–6 days, reaching 3.2–4.3 mm in length. They began feeding on cooked egg yolk and later on soy milk and fertilizer.
**Test Results**
- **Breeding Effect**: Out of 575 females, 114 were semi-productive, resulting in an egg production rate of 80.18%. Effective fertility was 49/g body weight.
- **Hatching Rate**: Three batches were produced, totaling 509.10 million larvae. The second batch showed a 15.38% drop in hatching rate due to residual enzymes.
- **Survival Rate**: Fry reached 19.87 mm in length, with over 3 million exceeding 24 mm. Survival rate was 95.7%, while that of wild fry was only 35%.
**Discussion**
- Early propagation using plastic greenhouses allowed fry to be released 20 days earlier than natural conditions, improving economic returns.
- Timing was crucial, especially when managing spawning based on weather changes. Water temperature and flow also influenced spawning success.
- Disease prevention, such as using methylene blue, improved hatching and survival rates.
- Early fry faced challenges due to cold temperatures, highlighting the need for controlled environments.
- Broodstock age played a role in fecundity, with best results from 2–6-year-old fish. Proper feeding ensured high fertility.
**Author**: Gansu Agricultural University
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