How to raise and manage fry
(1) Selection of fry ponds Selection criteria of fry ponds: It is required to be conducive to the growth, feeding management and net-pulling operation of fry. Specifically, the following conditions should be met:
First, sufficient water, convenient water injection and drainage, fresh water quality and no pollution. Because in the process of fry cultivation, water should be injected and changed at any time according to the growth and development needs of fry to ensure the growth of fry.
Second, the shape of the pond should be neat, and the best fish pond should be a sunny rectangle. The water temperature in this fish pond is easy to rise, the photosynthesis of phytoplankton is strong, and the phytoplankton reproduce vigorously, so; Is beneficial to the growth of fry.
Third, the area and water depth are suitable. The area is 0.067 ~ 0.2 hectares, and the water depth is 1. 5 meters. The area is too large, the feeding management is inconvenient, and the water quality and fertility are difficult to control; The area is too small, the change of water temperature and quality is difficult to control, the relative stocking density is small and the production efficiency is low.
Fourth, the bottom of the pool is flat, the thickness of silt is less than 20 cm, and there are no weeds. Too much silt makes the water quality easy to age, and too much oxygen consumption is not good for fry, and it is not convenient to pull the net. Aquatic plants absorb nutrients in pond water, which is not conducive to the reproduction of phytoplankton.
Fifth, the dam is firm and impervious, loam is the best substrate, but sand and clay are not suitable. Fish and leaking fish ponds are easy to form water flow, and the water flow at the top of fry is agglomerated, which consumes physical strength and affects feeding and growth.
(2) Cleaning and disinfection of fry ponds
1. Generally, fish ponds should be cleaned once a year 1 time, preferably after leaving the pond in autumn or winter. The method is as follows: firstly, drain the pond water, after sun exposure, kill pests and diseases and loosen the soil. At the same time, repair and reinforce the damaged ridge of the pond, plug the loopholes and cracks, level the bottom of the pond, remove weeds, dig out thick silt, accelerate the decomposition of organic matter and improve the fertility of the pond. The second drainage should be carried out before the fry are released 1 month. Further pruning after sun exposure creates good environmental conditions for fry growth.
2. Using drugs to kill wild fish, enemy creatures, fish parasites and pathogens is an important measure to improve water quality and increase the survival rate of fry. Generally, pond cleaning is carried out 10 ~ 12 days before the fry are released. If the time is too early, some pests often appear again when the fry are stocked; It is too late, the drug toxicity has not disappeared, and it is easy to poison the fry, or the pond water has not become fat, and the plankton is lacking, which affects the fry growth. Generally, the cleaning and disinfection of the North fry pond must be completed before May 10. Commonly used drugs and methods for clearing ponds are as follows:
(1) Quicklime pool cleaning: Quicklime pool cleaning is the most effective and economical method. The principle of action is: quicklime reacts chemically with water, releasing a lot of heat energy and producing calcium hydroxide, which can quickly increase the ph value of pond water to above 1 1 in a short time and kill wild fish and fish pests and pathogens. Quicklime can be divided into two methods: dry pool cleaning and pool cleaning. Generally, dry pool cleaning is adopted, and only when the water source is inconvenient or cannot be discharged into the pool water can the pool be cleaned with water.
Cleaning of dry pond: firstly, drain the pond water to 5 ~ 10 cm, dig several small pits at the bottom of the pond, pour the quicklime into the pits, add water to melt it, and spread it evenly on the edge and center of the whole pond without cooling, and the spreading amount is generally 75 ~ 150 kg/0.067 hectare (1 mu, the same below). In order to improve the effect of cleaning the pond, the bottom mud of the pond can be leveled with an iron rake the next day, so that the quicklime and sludge can be fully mixed. Don't drain the water completely when cleaning the pond, otherwise the loach will not die when it gets into the mud; In addition, the lime slurry is in contact with the air for too long, which leads to the precipitation of calcium carbonate, and it is impossible to clean the pool. Therefore, even if the pond is completely dried up after a winter exposure, water with a depth of 5 cm should be injected into the pond immediately after the lime slurry is evenly spilled to allow the lime to fully react.
Clean the pond with water; At the water depth of about 1 m, evenly pour the melted lime slurry into the pool while it is hot. The dosage is generally 150 ~ 250 kg /0.067 hectare. Precautions: ① The quicklime used for pool cleaning must be blocky, and the storage time should not be too long, otherwise the quicklime will absorb moisture and carbon dioxide in the air and gradually become powdered calcium phosphate and fail. (2) The main factors affecting the cleaning effect of quicklime pond are water hardness, ph value, quicklime quality, operation technology, water quantity in the pond and sludge quantity at the bottom of the pond. In production, the dosage of quicklime should be flexibly increased or decreased according to the changes of these factors. In ponds with high water hardness, low ph value and thick silt, the dosage of quicklime should be appropriately increased. (3) Built in saline-alkali wharf or pond with high alkalinity and pond in urgent need of fish; Do not use quicklime to clean the pond, but use bleaching powder to clean the pond. ④ Pool cleaning should be carried out in sunny and windless weather. In case of small wind, spray medicine in the downwind, and wear masks and gloves when operating to avoid personal injury. ⑤ After removing quicklime for 3 ~ 4 days, turn the bottom mud 1 time to make the unreacted quicklime fully react and avoid toxic effects after releasing fish. Then the pond can be filled with water. It takes 8 ~ 10 days to clear the pond with quicklime, and then fish can be put into the pond. The advantages of cleaning the pond with quicklime are as follows: when quicklime meets water, the ph value can rise to above 1 1, killing all living things and disinfecting thoroughly; Quicklime can loosen the structure of sediment, increase air permeability and accelerate the decomposition of organic matter in sludge. Due to the change of the colloidal structure of sludge, some nutrients such as nitrogen, phosphorus and potassium adsorbed by sediment are released, thus improving the fertility of pool water. Calcium itself is an indispensable nutrient element for animals and plants, and the application of quicklime can play a role in fertilization. Practice has proved that cleaning the pond with quicklime is equivalent to applying 1 times fertilizer to the pond, which is equivalent to applying 25 ~ 50 kilograms of manure per 0.067 hectare. Quicklime can also neutralize organic acids in sludge, buffer the content of carbon dioxide in water, keep the pool water at a stable pH value, which is neutral or alkaline, improve the water quality and is beneficial to the growth of fish. It can also promote the germination of rotifer winter eggs and is beneficial to the reproduction of zooplankton; The application of quicklime can reduce the turbidity of turbid pond water and is beneficial to the reproduction of phytoplankton.
(2) bleaching powder pool cleaning: the effect of bleaching powder pool cleaning is similar to that of quicklime, and its medicinal properties disappear quickly, so it is in urgent need of use.