How can static-water earthen ponds achieve high fish yields? Principles and techniques explained
Main aquaculture methods and yields
The main aquaculture methods include: static-water earthen pond culture, micro-flow water culture, flowing water culture, industrialized (recirculating) culture, reservoir and lake stocking, and rice paddy culture, etc.
Yields: cage culture, flowing water culture and industrialized culture give the highest yields, reaching more than 200 jin/m3, while static-water earthen ponds generally yield around 1000 jin per mu.
Why do intensive, high-density cage, flowing water and industrialized culture systems give high yields? Mainly because of the high stocking density per unit of water, the superior culture environment, the excellent culture species, and the comprehensive nutrition of the feed supplied.
To raise the yield per unit of water in static-water earthen ponds, one can draw on the conditions of intensive culture methods: try to increase the stocking density of the static pond, create a superior water environment, select excellent species, and feed a nutritionally complete diet.
The keys to the growth and survival of aquaculture species
1. Environment: Whatever the culture method, for the cultured species to survive there must be a suitable environment; the main environmental factors for aquaculture species are water quality and water temperature.
① Water quality: Aquaculture species must depend on water to survive; they not only dwell in water but live in it, breathe the dissolved oxygen in it, and also excrete metabolites into it. Therefore, for the cultured species to survive and grow better, a good water quality condition must be maintained throughout the aquaculture process.
The main aim is to raise the dissolved oxygen in the water and reduce the metabolites of the cultured species in the water; dissolved oxygen is positively correlated with the growth of the cultured species, while metabolites are negatively correlated with it.
② Water temperature: Aquaculture species are almost all poikilothermic (cold-blooded) animals, and their body temperature is closely related to water temperature; the body temperature of aquaculture species rises as water temperature rises and falls as water temperature falls. The physiological activity and metabolism of the cultured species are positively correlated with water temperature; within the suitable temperature range for the cultured species, the higher the water temperature, the stronger their metabolic capacity and the faster they grow.
In aquaculture activities, within the suitable temperature range for the cultured species, one should try to raise the water temperature to speed up the growth rate of the cultured species.
2. Nutrition: For the cultured species to survive and grow, it must carry out metabolism, and the material basis of metabolism is nutrition.
Different cultured species have different nutritional requirements; under natural conditions, silver carp and bighead carp mainly feed on plankton in the water, while mandarin fish and perch feed on aquatic insects and small fish.
Under artificial culture conditions, one should choose the most suitable feed according to the cultured species and try to meet its optimal nutritional requirements, so as to sustain its fastest growth needs. In actual farming practice, one must not only let the cultured species eat its fill but also let it eat well; the feed it takes in should be converted into flesh to the greatest possible extent.
3. Species: China has a vast territory, and the geographical and climatic conditions of the north and south differ greatly; under natural conditions, each region has its own unique native species. Therefore, in actual farming, one should not only choose species with excellent growth and economic traits, but also consider the suitability of the chosen species to the environment, as well as the market situation for the cultured species.
To carry out static-water earthen pond culture, one must first choose an excellent species suited to the local natural conditions and market demand; then during the culture process one must create a superior water environment, specifically by raising the dissolved oxygen in the water, reducing metabolites in the water, and raising the water temperature as much as possible within the suitable temperature range of the cultured species; next, one must feed a nutritionally complete, full-price feed; finally, one should choose the best time to harvest and sell the farmed product.
The key to raising the yield of static-water earthen ponds
In static-water earthen pond culture, choosing excellent, high-quality fry and fingerlings, creating a superior water environment, and providing nutritionally complete feed will bring each cultured individual to its best growth rate. Yield, however, refers to the growth of the population; to raise the culture yield, one must increase the stocking quantity and raise the stocking density. Under artificial culture conditions, if the environment is superior, the water temperature suitable and the nutrition adequate, then within a certain range, the greater the density, the higher the yield. Therefore, increasing stocking density is the key to raising the yield of static-water earthen pond culture.
Measures for high yield and increased income in static-water earthen ponds
1. Pond selection: An area of more than 5 mu; the pond can be filled with 1.5-2 m of water; little seepage and little silt; convenient water inlet and drainage; and a guaranteed electricity supply.
2. Preparation of machinery: Equip one automatic feeder per 5-7 mu, one 1.5-3 kW aerator, and a corresponding generator.
3. Pond clearing and preparation: Before stocking fry and fingerlings, drain the pond dry, clear the pond with quicklime or bleaching powder, repair the water inlet and drainage systems, sort out the electrical circuits, and set up the aerator and feeder.
4. Filling with water: Once maintenance and setup are done, the pond can be filled with water; choose a clean water source as far as possible, and fit a screen at the water inlet to prevent wild and trash fish from entering.
5. Stocking: When the water reaches 50 cm deep, the fry and fingerlings can be stocked. For market fish culture, the stocking number of the main feeding fish depends on the specific situation. It should be at least 1000 fish per mu, with a size of 80-150 g per fish (1.6-3 liang per fish); each mu can be polycultured with 200 silver carp and 100 bighead carp of 150-300 g per fish (3-6 liang per fish). Choose late autumn or early spring for stocking (water temperature around 10°C).
6. Feed: Those with the means can process feed themselves, but the formula must be nutritionally complete. Those without processing capacity should buy finished feed from reputable manufacturers.
Management techniques for high-yield static-water earthen ponds
1. Fry and fingerling stocking technique: Choose fry and fingerlings that are robust, disease-free and uninjured, and keep the size of the same species as uniform as possible. For summer fry, the stocking rate is 30,000-50,000 per mu, with appropriate polyculture of silver carp and bighead carp summer fry; clear the pond ten days before stocking the fry, then fill with water to 50 cm and apply 1000 jin of organic fertilizer per mu, aiming to reach the early peak of cladocerans when the fry are stocked; carry out temperature-acclimation treatment when stocking the fry. For market fish culture, stock the main species at 80-150 g per fish (1.6-3 liang per fish) and a density of more than 1000 fish per mu; clear the pond 5 days before stocking, then fill with water to 50 cm without applying organic fertilizer, and during stocking dip the fish in salt water in a holding box for disinfection.
2. Ecological temperature regulation technique: Fish are poikilothermic animals; within the suitable temperature range, the higher the temperature, the greater the fish's feed intake, the faster the metabolism, and the faster the growth.
In northern regions the day-night temperature difference is large: water temperature is lower in the morning and higher in the afternoon. How to make the water temperature rise as quickly as possible once the sun comes out is a problem that must be taken seriously in actual farming. Within a unit area, the deeper the water, the greater the volume of water stored, and the more heat is needed to raise the water temperature by the same amount; under the same heat source, it therefore takes longer.
Under natural conditions, pond water temperature is closely related to air temperature and also to light. For the same area, the shallower the pond water, the faster the water temperature rises as the air temperature gradually increases after the sun comes out; the deeper the pond water, the slower the water temperature rises. Therefore, water temperature is negatively correlated with water depth.
In production one must apply this flexibly: in the early stage of culture, that is, in late spring and early summer each year, the water depth can be kept at 50-80 cm; by late summer, the water depth can be kept at 1-1.5 m. This achieves the best use of air temperature and sunlight to regulate water temperature.
In late spring and early summer, the newly stocked fry and fingerlings weigh little, and the fish-carrying capacity per unit area of the pond is not very large either; as time goes on, the fish keep growing and the water gradually deepens, so the fish-carrying capacity per unit area increases, while the fish-carrying capacity per unit volume of water does not increase. In pond culture in northern regions, in the early stage one must absolutely avoid a water depth of more than 1 m: deep water warms slowly and fish grow slowly, whereas if the water is shallower it warms quickly, extending the fish's optimal growth time, thereby speeding up growth and raising the yield.
3. Biological water regulation technique: Many microorganisms live in the pond; they decompose fish feces, turning organic matter into inorganic matter and providing nutrients for the pond's phytoplankton. Phytoplankton not only produces oxygen but is also food for filter-feeding fish. To speed up this beneficial process, regularly (every 10-15 days) splash beneficial microbial preparations into the pond and add beneficial bacteria to the feed, so as to minimize the presence of fish metabolites.
4. Mechanical aeration technique: Under natural conditions, the dissolved oxygen in the water of a static-water earthen pond comes first from oxygen in the air dissolving into the water, and second from production by phytoplankton in the water. For a static-water earthen pond to achieve high yield, an aerator must be used for mechanical aeration. The specific way to run the aerator is: on sunny days, run it from 12:00 to 14:00 noon each day, and from 22:00 at night until the sun comes out in the morning; on cloudy and rainy days, run it 24 hours.
5. Automatic feeding technique: Equip an automatic feeder; based on the total standing stock of fish in the pond, determine the total daily feeding amount, allocate the amount for each feeding, and adjust the feeder properly. Each feeding should last 30-40 minutes, 2-4 times per day, and the feeding amount should be 2%-5% of fish body weight according to water temperature.
For market fish culture, the stocking density is greater than conventional, so the automatic feeder can be used for training from the start: first feed a small amount over a long time, and once all the fish have risen to the surface to feed, feed normally.
For fry culture, the stocking density is many times the conventional rate. After the fry are put into the pond, the natural food in the pond is quickly eaten up by them; first use the manual method of placing a small amount of feed at the feeding point, and when a large number of fry are feeding, begin using the automatic feeder for training, in the same way as training with an automatic feeder in market fish culture.
6. Scientific disease prevention technique: After properly disinfecting the pond, water source and fish stocks, regularly splash drugs to control bacteria and parasites into the pond and add them to the feed, so as to control the occurrence of fish diseases.