In recent years, the aquaculture industry has faced challenges due to rising feed costs and stagnant product prices, significantly impacting carp farming. However, grass carp, which requires lower-cost feed, has emerged as a promising species for intensive farming. Utilizing existing pond infrastructure for grass carp cultivation is an effective strategy to improve economic returns. Based on our practical experience, we have developed and refined several key techniques, which are outlined below.
**I. Pond Conditions and Water Quality**
1. **Pond Setup**: The ponds should be located away from pollution sources, with an area of 5–10 mu (approximately 3–6.7 acres). The bottom should be flat, with loamy soil preferred. A slight leakage is acceptable, and the mud layer should be between 10–20 cm deep. The water depth should be around 2 meters. Each pond must be equipped with a 3-kilowatt impeller aerator and a 4-inch pump for water exchange and aeration.
2. **Cleaning and Disinfection**: Grass carp are prone to diseases, especially in intensive environments. It's crucial to remove all other fish species to ensure proper feeding and reduce competition. During dry periods (with 5–10 cm of water), 100 grams of slaked lime or 10 kg of bleaching powder per mu should be applied after dissolving in warm water to thoroughly disinfect the pond and eliminate pathogens.
3. **Water Quality Management**: The pH should be maintained between 7.5 and 8.5. During the breeding season (June–September), water transparency should be around 30 cm, and the chemical oxygen demand (COD) should remain between 18–20 mg/L.
**II. Seed Selection and Stocking**
1. **Choosing Seedlings**: Select healthy, lively grass carp with a golden body color, no injuries, and a weight of about 100 grams. Due to the susceptibility of current strains to hemorrhagic and enteric diseases, it's advisable to choose two different seedling varieties.
2. **Stocking Density and Species Mix**: Typically, 800–1000 seedlings are stocked per pond, with individual sizes ranging from 250–500 grams. A mix of 100 carp species and 15 crucian carp species can be added to prevent grass carp from preying on smaller fish. Before stocking, fish should be disinfected at the surface.
**III. Feeding Practices**
Grass carp are primarily fed with finely chopped green fodder, supplemented by compound feed. The compound feed includes fishmeal, soybean meal, wheat bran, corn, and other ingredients, along with mineral salts, vitamins, and amino acids. It should provide a balanced diet with 20% crude protein, 4% crude fat, 40% carbohydrates, and 8–10% fiber. Green feed options include alfalfa, ryegrass, Sudan grass, and fresh aquatic plants.
**IV. Feeding and Management**
1. **Feeding Schedule**: Intensive feeding involves both conventional feed and bait. Feeding should be done at fixed times and locations, following the principles of quality, quantity, timing, and location. From March to May, feed 2–4 times daily; June to August, 3 times; and September to October, 4 times. Green feed is provided once daily, with amounts adjusted to avoid overfeeding.
2. **Bait Preparation**: Sulfaguanidine is used to make floating bait. Mix 5 grams of sulfaguanidine with 1 kg of bran, add licorice bark or sweet potato flour, mix with hot water, press into small pieces, and dry for use. Feed according to fish weight, starting with 1 kg per 10 kg of fish, then reducing by half for 2–6 days. Repeat this cycle monthly.
3. **Water Quality Control**: Regularly apply lime (20 kg per mu, 20 cm water depth) or 1 ppm of bleaching powder every 15 days. Change water every 10 days, adding 20–30 cm each time. By mid-July, change half the water based on conditions. Run the aerator daily, especially during June to August, to prevent oxygen depletion. Monitor fish behavior and water quality regularly, and clean debris and leftover plant material from the pond.
**V. Disease Prevention**
1. **Intestinal Diseases**: Use the above-mentioned bait feeding method as a preventive measure.
2. **Gill Diseases**: Treat with erythromycin (0.07 ppm on day one, followed by oral administration of 1 g per 100 kg of fish for 2–6 days). For gill and enteric complications, use gallnut and furazolidone: boil gallnut and drip into the pond at 1.4–3.0 ppm, while feeding furazolidone at 1 mg per 100 kg daily for 6 days.
3. **Skin Diseases**: Apply general bactericidal agents such as Fish & Shrimp Enemy Spirit or Fish Disease Spirit.
By implementing these comprehensive management strategies, farmers can significantly enhance the productivity and profitability of grass carp farming.
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