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Freshwater pond fish health breeding technology
The "Healthy Breeding Technology of Fish in a Fresh-Breed Pond" is a key aquatic product promotion and development project under the Ministry of Agriculture, initiated in 1999. This project focuses on improving fish breeding methods through advanced pond management techniques. Below are the major technologies and practices involved:
Ponds selected for brackish water fish farming should be located near estuaries with access to saline water sources. They must have tidal or irrigation and drainage systems, ensuring proper water flow. The salinity of the water should range from 0.5‰ to 16‰, with a pH between 6.8 and 8.2, meeting national fishery water quality standards. Each pond typically spans 5 to 15 acres, with a maximum size of 30 acres, and has a depth of 1.8 to 2.5 meters. These ponds are equipped with aerators, and some also use automatic sprayers to maintain optimal conditions.
The typical usage period of a pond is 5 to 7 years. After this time, the pond must be dried, exposed to sunlight, and thoroughly renovated. This includes deepening and dredging the drainage and irrigation channels. Bulldozers and dredgers are used to remove silt and sludge, increasing the pond’s depth to 3–3.2 meters. The effective water depth becomes 2.5–2.8 meters, with a bank slope ratio of 1:2.5. The embankment base is 5 meters wide, while the main base is 8 meters.
After one year of use, the pond is dried, and the bottom is cracked to remove sludge. Quicklime (100–150 kg per acre) is then applied before introducing fish. Before stocking, the water is "purified." If the water maintains a green or yellow-green color, it indicates successful culture. Water color and transparency are critical indicators of water quality. In saltwater ponds, the dominant algae are Chlorella, Chlamydomonas, and Cyclotella, giving the water a green or brown-green hue with a transparency of 30–40 cm. Care must be taken to control diatom overgrowth, bare algae, and cyanobacteria, as well as legged and copepod populations, to ensure stable water conditions.
Among the 11,126.25 mu of brackish water ponds managed under this project, all fish species were initially raised using natural or artificial seedlings. Their feeding habits changed as they grew, requiring adjustments in feeding strategies. Young fish often live in high-salinity environments but gradually adapt to lower salinities. Under artificial breeding conditions, variations in genetics, rearing techniques, and feeding abilities lead to differences in growth rates. To achieve uniformity, intermediate cultivation is essential, involving domestication, grading, and artificial feeding methods such as net cages and small earthen ponds.
Net cages made of nylon mesh (6–20 square meters, 1.2–1.5 meters deep) are commonly used. Stocking densities vary depending on species and size. For example, flower buds and barramundi at 3 cm are stocked at 150–200 per square meter, while yellowfin at 1.5–2.5 cm are stocked at 300–350 per square meter. After 20–25 days, fish grow to 5 cm and 3 cm, respectively, and are transferred to larger ponds. Stocking density is adjusted to 15–25 per square meter for further growth. Similar methods apply to other species like cockroaches, snappers, and small fish, based on their feeding behavior.
Domestication involves adapting juvenile fish from natural habitats to pond environments. During desalination, the daily salinity drop should not exceed 5 ppm. Artificial feeding methods replace natural prey, such as rotifers and copepods, with pellets or soft feeds.
Feeding strategies include monoculture, intercropping, and polyculture. Monoculture suits carnivorous fish, while intercropping involves raising one main species with a secondary one. Polyculture improves resource use and reduces disease risk but requires careful selection of compatible species.
Optimal stocking density depends on factors like survival rate, growth rate, and feed efficiency. Protein levels in feed range from 22% to 50%, but balance of amino acids is crucial. Imbalanced protein can increase nitrogen excretion, reduce growth, and harm water quality.
Feed types include powder, soft pellets, dry particles, and extruded pellets. Herbivorous diets are used for omnivorous species, while carnivorous species rely on pelleted feeds. Feeding methods vary: some fish are fed manually at fixed points, others via baskets, and some by spraying. Feed amounts generally range from 2% to 5% of the total fish weight, depending on age and stage.