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Cultivating fish species
Fish species are typically classified into two stages: fry and fingerlings, based on their developmental phase. Fry refers to newly hatched fish from eggs, while fingerlings are the juvenile stage that follows after several growth phases. The transition from fry to fingerling generally involves three distinct stages: the summer flower stage, the first-year fingerling stage, and the second-instar fingerling stage.
The first stage is known as the summer flower phase, which lasts approximately 20 to 30 days. During this time, the fry is small, fragile, and has limited mobility and adaptability. Therefore, careful attention is required during breeding to ensure their survival. Fish ponds should be chosen where irrigation is convenient, the soil is fertile, and water retention is good. The pond size should be manageable, ideally between 1 to 2 mu (about 0.67 to 1.33 acres). About one and a half months before the fry hatch, the pond must be cleaned and disinfected using lime or bleach. The water depth should be around 0.5 to 1 meter.
Feeding is crucial during this early stage. Fry primarily feed on zooplankton, with some supplemental soy milk provided by farmers. To support natural food sources, the pond should be fertilized with organic waste, green manure, or chemical fertilizers. A common practice is to apply 50–100 kg of green manure per acre 3–5 days before introducing the fry. If rapid fertilization is needed, nitrogen-based fertilizers can be used. Water quality should be monitored regularly, and top-dressing should be adjusted based on the clarity of the water, weather conditions, and the fry’s development. Ideal water color is tea brown or yellowish green.
Soy milk should be prepared by boiling and grinding soybeans, then evenly distributed in the pond. Approximately 2.5 kg of beans are used daily, with multiple feedings throughout the day. When feeding squid or similar species, the milk should be spread evenly across the pond. For grass carp and other species, more soy milk should be applied near the edges.
The second stage is the cultivation of first-year fingerlings. After about a month, the fry grow to around 3.3 cm and are called summer flowers. Though slightly stronger, they are still not ready for adult fish farming and need further development. By fall, they reach 12–15 cm and become first-year fingerlings. It's important to separate different fish species by size during this phase.
Polyculture—raising multiple fish species together—is often more efficient than keeping them isolated. While there are no strict rules, it's common to have 70–80% of the pond occupied by omnivorous species like silver carp, with 20–30% being herbivores or carnivores. Fertilization is key in these ponds to cultivate plankton, while supplementary feeds like soy milk, bran, and grain flour are also used. Feeding is usually done twice daily at designated feeding stations, with bait amounts adjusted based on fish size to avoid overfeeding or underfeeding.
During the first-year fingerling stage, fish grow rapidly, and size differences become noticeable. Regular monitoring and sorting help improve survival rates and promote uniform growth. Many farmers now focus on raising larger fingerlings, aiming for sizes over 15 cm and 50 grams, which significantly improves the quality of adult fish.
In the second year, first-year fingerlings are raised at a density of 1,000–2,000 per acre. After one year, they grow to 150–250 grams and become second-instar fingerlings. This stage benefits from a combination of feeding and fertilization, leading to high survival and fast growth. Techniques such as early stocking and timely pond separation can further boost production.