Hezhuang is a remarkable example of goldfish culture, known for its elegant appearance and lively movements. Its body shines with silver-white scales, while a bright red head crest adds a striking contrast. This combination of colors creates a vivid and refreshing visual effect, making the fish look as if it's flying like a crane. Hezhuang not only captivates with its beauty but also stands out for its graceful behavior.
**1. Breeding of Broodstock**
The breeding process begins in March each year. Female fish are selected from those aged 2 to 3 years, while males are usually 1 to 2 years old, maintaining a ratio of 1:1.2. The selection focuses on fish with a well-defined red head crest, while irregular coloration such as yellow or white is typically avoided. The stocking density is lower than that of commercial fish, and feeding is gradually increased as temperatures rise. It generally takes about one month for the gonads to fully mature.
**2. Selection of Broodstock**
By mid-April, the broodstock can be evaluated. Females should have a soft and elastic abdomen, and their bodies should be oval-shaped. They are identified using micro-infrared techniques. Males, on the other hand, should have full, flowing fins and show active chasing behavior, indicating their readiness for breeding.
**3. Artificial Oxytocin Injections**
In mid-April, when the water temperature reaches around 25°C, artificial oxytocin is administered. A disposable pectoral fin injection method is used. For every 100g of female fish, 1-2 μg of luteinizing hormone-releasing hormone analogue (LRH-A2) is injected, while male fish receive half the dose. The injections are carried out around midnight, and the fish are kept in a squatting position for 18-20 hours.
**4. Artificial Insemination and Hatching**
During the evening, when males begin to actively pursue females, both are quickly transferred into a container filled with water. Their eggs and milt are gently extracted and mixed in a sterile basin containing a small amount of 25°C normal saline. The process involves careful handling to ensure even distribution of the fertilized eggs in the hatching tank.
During incubation, clean, non-polluted water with sufficient dissolved oxygen is essential. The pH should be maintained between 7.5 and 8.0, and at a water temperature of 25°C, the eggs will hatch within 3 to 4 days. To prevent fungal infections, a 10ppm malachite green solution is added daily, and fresh water is regularly introduced.
**Rearing of Fry**
Freshly hatched larvae rely on their yolk sacs for nourishment. After four days, they are fed cooked eggs through a 25# plankton net, ensuring the yolk remains suspended in the water. Feeding is done once daily, and the amount is adjusted based on how much is consumed within 1 to 1.5 hours. By day eight, the larvae grow to over 1 cm, showing improved swimming ability and starting to feed on small plankton. At 3 cm, the water is changed weekly, and larval feed is introduced.
**Advantages of Artificial Insemination**
Artificial insemination significantly reduces the physical stress on broodstock, lowering mortality rates. Studies have shown that post-breeding survival rates can increase from 50% to 75% with natural mating to over 95% with artificial methods. Additionally, the fertilization rate improves from under 40% with natural mating to more than 80% with artificial techniques. It also helps maintain genetic purity.
**Notes**
The fish nests should be placed in the middle and upper layers of the water, with weights attached to both sides. They should be lifted and fixed in the hatching pool. If the nest rises above the water surface, the eggs may be exposed to sunlight and sink, leading to suffocation. During the first three days of incubation, the eggs must not be turned randomly, as this can reduce hatching success and lead to deformities.
(Southwest Agricultural University, Department of Fisheries – Yu Xiaodong)
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