The fry cultivation includes the gradual removal of the yolk sac from the fish, the formation of fish gills and the enhancement of swimming ability from the time of the release of the fish. The stocking of 1 million-1.1 million tails per acre can be produced, and after 25-30 days of intensive cultivation, 700,000-800,000 2.3-2.5 cm fry can be produced.
I. Preparation before stocking
1. Pond conditions Fish nursery pond area is generally 2-4 acres is appropriate, depth 1.5 meters, the pond sludge thickness is less than 20 cm, the bottom of the pool is flat, pond pool is strong and solid, no leakage. It requires sufficient water, fresh water, and convenient drainage.
2. About 20 days before the ponds are cleaned and disinfected, the water in the pool is exposed to sunlight to kill the harmful microorganisms at the bottom of the pond, accelerate the decomposition of some organic substances, and improve the fertility of the sediment. The weeds in the surrounding area of ​​the pond and the debris in the pond are removed, and the pool raft is reinforced to facilitate the operation of the net. After 5-6 days of exposure, dry disinfection was carried out. Each kilogram was sprayed with 75 kilograms of quicklime pulp.
3. Fill fresh water and add new water after one week of disinfection. The inlet is filtered with a 60-mesh screen to prevent harmful organisms from carrying water. Do not add too much water for the first time, 30--40 cm can be, this is conducive to rapid fertilizer and permanent quality control.
4. Fertilizer Water Quality In general, a large amount of plankton will appear 7-10 days after the sun exposure and disinfecting pond water injection, and the water color is dark brown. The depth of the water is related to the weather. When the weather is fine, the color of the water becomes darker, and vice versa. For the lean water quality, the decomposed organic fertilizer can be added in front of the fish pond. After the water is fertilized, the plankton contains more plankton, especially the fry bait organisms, and the fry can be released.
Second, fry stocking
1. After the release of the fish fry for 2 to 3 days, the body length is about 7-10.5 mm and the body weight is about 2 mg. At this time, the fish body has a yolk sac, and the waist point has not yet formed, and it cannot swim flexibly.
2. Stocking time fry stocking time should be selected in the sunny morning, it is best to have sunny weather for several days, which is crucial to improve the survival rate of fry.
3. Stocking densities of 1 million and 1.1 million tails per acre are better, ponds are poorer, and water quality is not enough to reduce stocking.
4. The stocking method of spray generally adopts nylon bags to transport oxygen, and should be placed on the surface for 20-30 minutes before opening the bag mouth to buffer the water temperature to prevent the temperature difference from causing the fry emergency response. When stocking, let the aquatic fish fry flow into the pool with water and avoid falling into the water.
Third, feeding and management
1. Feeding
Zooplankton are the open bait of fry. They can only feed on small zooplankton at the beginning, and they can ingest larger zooplankton as they grow. This stage is dominated by splashing soy milk. The effect of soymilk is actually water and fertilizer, because the fry is still unable to ingest soy milk particles.
When the fry grows to about 1.5 centimeters, it begins to change its diet and gradually changes from carnivorous to omnivorous (except for carnivorous fish). The swimming ability of the fish body was significantly enhanced, and the activity range spread from the "seamless" of the early Xitang to the middle of the pond. At this stage, splashing soymilk should also be changed from “sliding†to splashing in the middle of the pond. The amount of soybeans should be 4.5-5 kilograms per acre per day, divided by 2-3 times.
When the fish body is 1.8 centimeters long, the fry have become omnivorous, and the amount of soy milk to be fed is 5-6 kilograms per mu per day, which can be divided into 2 times.
Splashing soymilk should pay close attention to fish growth and weather changes. Pool fish density, should adjust the amount of feeding. The weather is fine, the fry activity is strong, and should be added. If it is cloudy, it should be reduced. In rainy days, it can be fed less or not.
2. Water quality management
Fish fry use plankton as an open bait, so it is necessary to maintain the water's fatness, that is, to ensure that there are enough food organisms. There are mainly two methods for cultivating plankton: the first is to increase or decrease the amount of splashed milk, which is also the main and effective way; the second is to cultivate organic plankton by applying organic fertilizer. The fry cultivation phase takes 25-30 days, during which 4-5 fresh water injections are required. Generally, 15-20 cm of water is added each time, and the final water level is controlled to be less than 1.2 meters. This facilitates the subsequent operation of the net and increases the growth of fry. Space; on the other hand improve water quality and promote fish growth. In the late fry rearing period, after the water is added, it can be seen that the fish is so fierce that the so-called “water-inch fishâ€.
3. Pull exercise
Due to the random error of the water-spray count and the difference in the pond conditions, the fluctuation of the actual number of self-fries in each pond will affect the growth of the fry to a certain extent, and it will not be convenient for production management. Therefore, a net check is required. The pond culture density was adjusted in time. At the same time, pulling the net operation is also a training process for the fish fry. Practice has shown that fry-racing fish has good long-distance transport tolerance. The time for drawing a net to exercise is more than 2.0 centimeters long. The operation should be careful and the speed of movement should be slow. There should be at least 1-2 times of wire-drawing and training before frying or digging the pond.
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