How to Increase the Current-Year Yield in Grass Carp Farming
The key to increasing the current-year yield of grass carp fingerlings is that the rearing and management methods must conform to the living habits of grass carp, achieving and maintaining clean water quality, no sources of disease, high dissolved oxygen, suitable feed, and timely disease prevention and control measures.
1. Do a good job of pond disinfection and fish body disinfection
For ponds used to rear fingerlings, by no means should you disinfect the pond while it is dry or disinfect it with shallow water, because if you do so, you must add water before stocking the grass carp fingerlings, which will carry pathogens into the already disinfected pond and increase the sources of infection. Therefore, after filling the pond to the normal fish-rearing water level, 20 days before stocking the fingerlings, use 150 kg of quicklime per mu per meter of water depth, slake it into lime milk and splash it over the whole pond for disinfection. The slopes around the fish pond should also be splashed, and at the same time weeds should be cleared to prevent insects from laying eggs in the pond.
Fish body disinfection is a task that must be done before summer fry are put into the pond. If undisinfected fingerlings are allowed to enter the pond directly, they will bring in pathogens. Under certain conditions, such as suitable water temperature, water quality, and weak fish constitution, the pathogens will develop rapidly and cause an outbreak of fish disease, making all the pond-clearing and disinfection work wasted. For fish body disinfection, generally use a 5% concentration salt water dip, or bathe with a 20 ppm potassium permanganate solution, to eliminate parasites and bacteria on the fish body surface. The method is: put the counted fish into a larger container, calculate the water volume of the container, then calculate the amount of medicine to use. The soaking time for the fish body should be decided according to the fish constitution, water temperature, and other conditions, generally 15-20 minutes. If the grass carp are found floating at the surface, it indicates that the water is short of oxygen and the fish cannot endure it; at this point quickly release the fish into the pond.
How to increase the current-year yield of grass carp
The key to increasing the current-year yield of grass carp fingerlings is that the rearing and management methods must conform to the living habits of grass carp, achieving and maintaining clean water quality, no sources of disease, high dissolved oxygen, suitable feed, and timely disease prevention and control measures.
1. Do a good job of pond disinfection and fish body disinfection
For ponds used to rear fingerlings, by no means should you disinfect the pond while it is dry or disinfect it with shallow water, because if you do so, you must add water before stocking the grass carp fingerlings, which will carry pathogens into the already disinfected pond and increase the sources of infection. Therefore, after filling the pond to the normal fish-rearing water level, 20 days before stocking the fingerlings, use 150 kg of quicklime per mu per meter of water depth, slake it into lime milk and splash it over the whole pond for disinfection. The slopes around the fish pond should also be splashed, and at the same time weeds should be cleared to prevent insects from laying eggs in the pond.
Fish body disinfection is a task that must be done before summer fry are put into the pond. If undisinfected fingerlings are allowed to enter the pond directly, they will bring in pathogens. Under certain conditions, such as suitable water temperature, water quality, and weak fish constitution, the pathogens will develop rapidly and cause an outbreak of fish disease, making all the pond-clearing and disinfection work wasted. For fish body disinfection, generally use a 5% concentration salt water dip, or bathe with a 20 ppm potassium permanganate solution, to eliminate parasites and bacteria on the fish body surface. The method is: put the counted fish into a larger container, calculate the water volume of the container, then calculate the amount of medicine to use. The soaking time for the fish body should be decided according to the fish constitution, water temperature, and other conditions, generally 15-20 minutes. If the grass carp are found floating at the surface, it indicates that the water is short of oxygen and the fish cannot endure it; at this point quickly release the fish into the pond.
2. Cultivate fresh, live, and suitable bait
After the fish pond is disinfected, about 10 days before the summer fry are put into the pond, apply 300-400 kg per mu of organic fertilizer as base fertilizer. Every 2-3 days, splash the whole pond with 30-40 kg of manure water per mu, or 1 kg of urea plus 0.5 kg of superphosphate after dilution, to cultivate large numbers of water fleas and accelerate the division and reproduction of watermeal and small duckweed, so that when the grass carp summer fry enter the pond they can eat abundant fresh and live suitable bait. During the water quality cultivation stage, observe changes in water quality at all times, remove frog eggs promptly when found, and if large numbers of blue-green algae appear, splash the whole pond with 0.7 ppm copper sulfate.
3. Change the traditional fingerling stocking method
In production practice, I changed the traditional method of mixed rearing grass carp fingerlings in silver carp and bighead carp ponds, and adopted the method of sparse stocking and main rearing. This conforms to the habitual requirements of grass carp. Sparse stocking of grass carp fingerlings can produce large-sized, good-quality fingerlings. To solve the problem of grass carp feces decomposition making the water quality become fertile, a small number of silver carp and bighead carp can also be added, but no additional bait or fertilizer is applied; only the plankton cultivated from grass carp excrement is used as bait. For a pond mainly rearing grass carp fingerlings, 8,000 grass carp of 4-5 cm can be stocked per mu, together with 1,000 silver carp and bighead carp (the ratio of silver carp to bighead carp is 4:1), and 400 crucian carp and bream. When stocking, grass carp should be stocked 15-20 days earlier than the other accompanying fish, to benefit the growth of grass carp and increase the survival rate.
4. Rearing and management methods
When grass carp summer fry enter the pond, they are not yet adapted to eating green feed, so soybean milk and soybean cake slurry must be fed to increase the survival rate of grass carp fingerlings and speed up growth. Use 1-3 kg of soybeans per 10,000 fry per day, soak each kg of soybeans well in 15 kg of clean water, and do not add extra water when grinding the slurry.
When the grass carp grow to 5-7 cm and can eat watermeal, soybean milk no longer needs to be fed. Watermeal is rich in nutrients, is favored by grass carp and easy to digest, and does not pollute the water quality. Many years of practice show that using watermeal to rear grass carp fingerlings gives fingerlings with a good constitution, strong disease resistance, and few diseases. Several feeding grounds can be enclosed around the pond separately, preferably 4 per mu. Put watermeal and the like into the feeding grounds, and feed twice a day. The amount put in is decided according to the feeding situation of the grass carp, with the limit being eaten up within 4-5 hours. At the end of September, when the growth of watermeal is nearing its end, use crushed rapeseed cake or soybean cake, 10 kg per mu per day, in two feedings in the morning and afternoon, placed on feeding platforms set up under the water, until the fingerlings are concentrated into ponds.
During the rearing period, also insist on patrolling the pond every day in the morning, at noon, and in the evening: check the floating condition of the fish in the morning, check the activity of the fish at noon, and check the water quality in the evening. Frequently remove leftover bait, frequently prevent fish diseases, regularly turn on the aerator, promptly catch harmful creatures that enter the pond, carefully keep pond records, and promptly deal with any problems found.
5. Manage water quality well
For ponds mainly rearing grass carp fingerlings, the water transparency is required to be 50--60 cm. However, after grass carp fingerlings feed heavily, their own excrement will also affect changes in water quality, so in the early stocking period add water once every 3-5 days, and in July-August add water once every 2-3 days, 5-10 cm each time, so that the water body always remains fertile, lively, tender, and refreshing, providing a good growth environment for the grass carp. When changing water, pay attention to preventing fingerlings from escaping and wild miscellaneous fish from entering.
6. Do a good job of fish disease prevention and control
In seasons when fish diseases are prevalent, regularly use a combination of splashing medicines and oral medicated bait to prevent and control fish diseases. From mid-June to early October, every 10 days alternately splash quicklime (per mu with 1 meter water depth, amount 20 kg) and bleaching powder (per mu with 1 meter water depth, amount 700 g, chlorine content 30%) for disinfection. Every 15 days feed medicated bait for three consecutive days. The method is: for every 100 kg of fish, dissolve 10 g of allicin in water, mix evenly with a small amount of adhesive, and evenly splash it on the watermeal. While turning the watermeal, after 15 minutes, when the medicinal liquid and watermeal have stuck firmly, put it into the feeding ground. Or for every 100 kg of fish, dissolve 5 g of "Grass Carp Three Diseases Remedy" in 2.5 kg of water, add 10 kg of dry barley, wait until the liquid is absorbed, then add 2 kg of water until the barley is fully swollen, and feed continuously for three days. These methods can be used as prevention and also as treatment; the condition can be resolved after one course of treatment. Persisting with the above methods for routine prevention and control of fish diseases will bring the sources of disease under control and eliminate them, and pond fish will rarely become diseased.