There are numerous breeds of freshwater fish, and a wide range of aquaculture models exist. Across the country, more than a dozen farming methods have been developed based on water conditions, species, and other environmental factors. While it's not possible to detail all of them here, we will focus on introducing a few key fish farming techniques, particularly those related to fertilization methods and practices.
First, pond fish fertilization is still widely practiced in certain areas of Central China, such as Sichuan and Chongqing, where traditional breeding methods involving eels and similar species remain popular.
**Cultivation Conditions**: The ideal pond area ranges from 5 to 20 acres, with a depth of 1.5 to 3 meters and a bottom mud layer of 10 to 20 cm. The location should be near a reliable water source for easy irrigation and drainage.
**Culture Characteristics**: This method relies on the natural material cycle among organisms to reduce production costs. After applying fish fertilizers, plankton populations increase, boosting the primary productivity of the water. Phytoplankton helps raise dissolved oxygen levels, speeds up organic matter decomposition, and provides ample food for fish, promoting their growth and improving overall pond productivity.
**Cultivated Species**: The main species raised are whitefish, accompanied by smaller mid- and bottom-dwelling fish like grass carp, silver carp, and bighead carp.
**Stocking Ratio**: The typical distribution is around 70-80% silver carp, 5-10% bighead carp, 10% grass carp, and 5% other species. Stocking size is usually 11.6–13.2 cm in autumn, with about 200–300 fish per acre. If needed, spring stocking can supplement the numbers, keeping the total between 700–800 fish per mu, weighing 17–18 kg.
**Preparation for Stocking**: Seven to ten days before stocking, ponds should be cleaned using lime or drugs, preferably on sunny afternoons.
**Feeding Management**:
1. **Base Fertilization**: From mid-April to mid-May, apply "Tianchen Fish Fertilizer" or traditional fertilizers in stages. At this time, the amount is 2–3 times the normal level, aiming for good water quality. Sludge or newly dug ponds require more fertilizer.
2. **Top Dressing**: Starting in June, regular top dressing is necessary. As temperatures rise, avoid traditional agricultural fertilizers and use "Tianchen Fish Manure" instead. In June, apply 4–5 times a month at 2–3 kg per mu. By July and August, increase to 5–7 times monthly, adjusting based on conditions. Reduce frequency after September.
3. **Fertilization Management**: After May, regularly add fresh water. Every 20–30 days, apply quicklime to keep the water clean and prevent diseases. Maintain pH between 7.3 and 7.8.
**Harvesting**: Using these methods, after one year of rearing, the average weight of silver carp reaches 0.75–1.0 kg, while bighead carp can reach 0.75–1.2 kg. Harvesting should be done at optimal times for balanced yield.
Second, high-density pond culture is becoming more common, especially with the use of compound feed. Many farmers have transitioned from feeding white mullet to more intensive feeding of grass carp, silver carp, and others, though fertilizing remains essential.
Let’s take a look at the model of 1200 kg per mu:
**Cultivation Conditions**: Ponds should be 5–30 mu in size, with a water depth of 1.5–3 meters and convenient access to water sources.
**Culture Characteristics**: High-quality exogenous nutrients, such as compound feeds, provide adequate nutrition. Feed residue and fish waste act as natural fertilizers, promoting the growth of silver carp.
**Cultivated Species**: Silver carp, bighead carp, grass carp, herring, squid, and stingrays are commonly raised.
**Stocking Density**: Typically, 300 silver carp/acre, 50 bighead carp/acre, 150 grass carp/mu, 90 squid/mu, 400 crucian carp/acre, 400 mullet/acre, and 250 sturgeon/acre.
**Preparation for Stocking**: 7–10 days before stocking, disinfect the pond using lime or drugs on sunny afternoons. Fish should also be disinfected before being introduced.
**Fertilization and Feeding Management**:
1. Understand the behavior of the cultured species.
2. Follow the "three observations and four determinations" principle: observe weather, water color, and fish activity; determine timing, location, quantity, and quality of feeding.
3. Maintain good water quality by ensuring it is rich, lively, tender, and cool. When transparency exceeds 35 cm, apply "Tianchen Fish Fat" at 2–3 kg/acre to help regulate water quality and prevent disease.
4. Use aerators and perform full-pool disinfection to minimize disease outbreaks.
**Harvesting**: After one year, yields typically reach 300 kg/mu for silver carp, 500 kg/mu for bighead carp, 200 kg/mu for grass carp, 180 kg/mu for herring, 200 kg/mu for carp, 130 kg/mu for crucian carp, and 30 kg/mu for stingrays, totaling 1100–1200 kg/mu.
Third, small and medium-sized reservoirs are increasingly adopting semi-intensive culture methods. With rising market prices, many reservoirs now combine fertilization with artificial feeding.
**Cultivation Conditions**: Reservoirs should be well-watered, with open surfaces and strong sunlight. Water exchange should be infrequent, and there should be facilities to trap fish. The water depth should not be too deep.
**Culture Characteristics**: These large bodies of water, ranging from tens to thousands of mu, are easily managed. They offer excellent water quality and are suitable for cultivating various fish species.
**Cultivated Species**: Grass carp, silver carp, and bighead carp are dominant, with a small number of high-value fish also raised.
**Stocking Density**: Typically, 80–85% silver carp, 15–20% bighead carp, with an appropriate amount of grass carp. Seedlings should be larger, generally 3–4 per fish, with larger ones reaching 8–10 catties. Stocking density varies depending on the reservoir, with 150–250 fish/mu for highly fertile reservoirs and 100–150 fish/mu for ordinary ones. Fish should be uniform in size, healthy, and free from disease.
**Preparation for Stocking**: Disinfect fish species before introduction. Apply a large amount of agricultural fertilizer or "Tianchen Fishery Fertilizer" to the reservoir before stocking.
**Fertilization Management**:
1. Apply base fertilizer before and after stocking, combining traditional and "Tianchen Fishery" fertilizers.
2. For high-density stockings, maintain water clarity at 30–40 cm.
3. When water temperature is 20°C, plankton peaks 4–5 days after application and lasts 7–8 days. Reapply every 13–15 days. At 25°C, plankton returns to pre-fertilization levels after 5–6 days and lasts 6–7 days. Apply top dressing every 10 days. From June to August, apply fertilizer every 3–4 days and adjust accordingly.
4. Apply fertilizers in bays or upwind areas, best done at noon on sunny days.
5. Keep pH between 7.3 and 7.8. If acidic, apply lime first, then wait two days before fertilizing.
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