Reasons and Countermeasures for Low Survival Rate of Fry Cultivation

Spring is coming and the season of fry cultivation is coming. In recent days, we have received letters from friends of some fish farmers, reflecting the low survival rate of the fry and fish fry they purchased, and some even annihilated. Why is this? How can I solve it? To this end, we specifically conducted field surveys on some customers in Xichang, Yunnan, Henan, and Hubei, and discussed discussions with farmers. We now summarize our views as follows: 1. The condition of fish nursery ponds is poor. In the survey, we found that about half or more of the fry pools are in poor or very poor conditions, such as the size of a single pond, or the depth of the water body, or the depth of mud that has been lost to cultivation for many years. Due to the large area, the wind and waves are large. The tender and fragrant fish seedlings will suffer partial loss under the slap of wind and waves in the nearshore. Because the pool water is too deep and the mud is thick, the water temperature rises very slowly, and the fish seedlings may easily sink to the bottom and form a stiff seedling. The strategy is to use a fish pond with a single pond area of ​​3 mu or less and a sediment thickness of no more than 20 cm as a cultivation pond. The water depth during the seedling control is controlled at about 40 to 50 cm. 2. There are too many enemy creatures in the fish pond. Because there are quite a number of fish ponds that do not have clear ponds, or clear ponds are not thorough, or use drugs that have already expired, or eggs, seedlings, and other predator organisms that are mixed with wild fish in the water injection, they compete with the fish for food and competition. Oxygen even eat fry. The countermeasures must be strict and thorough disinfection of clear ponds, and the effect of using block-like quick-lime clear ponds that have just been discharged from the kiln is good; when water injection is performed, double-layer eye mesh must be added at the intake to intercept enemy-damaged creatures. 3. The residual toxicity in the fry pool is large. Due to the large dosage of drugs and the low water temperature in the clear ponds, the drug power has not completely disappeared, or due to the excessive application of organic fertilizers that are not fully cooked or underperforming, as a result of the excessive use of base fertilizers, resulting in high concentrations of hypoxia or toxic and harmful substances in the bottom water. The seedlings that had just been put into the pool died in large numbers and were even wiped out. The solution is to grasp the appropriate amount of pesticides and fertilizers. Put a small cage or a bucket of water in the pool before placing the seedlings. Put a few fry before testing the water. If there is no abnormality in these test fish fry within 4 to 8 hours. The reaction can put fish into the pool. 4, Fangmiao is unreasonable. The most common phenomenon is that the seedling density is high and the seedling time is early. Sometimes, different batches of fry are put together with one pool or different types of fry are also put together with one pool. Sometimes the details such as adjusting the temperature difference are ignored. The countermeasures are based on fish pond conditions, different species, local climate change patterns and production management levels. The result of "greatness" is often that the fry grows slowly and is also prone to have an outbreak of disease; "crazy early" often causes heavy losses due to the strong cold wave. In addition, avoid placing seedlings in the sun, otherwise there may be bubble disease; also can not put a few batches of seedlings or several seedlings into the same pool, otherwise there will be large seedlings to eat seedlings, strong seedlings to eat weak seedlings phenomenon, and the fish developed Varieties of different sizes, specifications vary; fry stocked fry must be "temperature adjustment", do not make the temperature difference exceeds 2 °C, otherwise it is easy to cause a large number of dead seedlings. 5, lack of palatability food. Many farmers do not pay attention to fertilizing water, or although the base fertilizer is applied, because the fertilization time is not well connected with the time of the fish pond, the fish is starved or grows poorly because of lack of food. The countermeasures are: (1) The fry pool is completely dry in the winter, and is exposed to the sun and frost. This will help to destroy the enemy pests (such as astragalus, loach, insects, etc.), is conducive to the decomposition of organic matter at the bottom of the pool, is conducive to fertilization pond water; (2) determined according to the bottom mud thickness of the fry pool, fertilizer types, water temperature and other conditions Appropriate basal fertilizer application rate, fertilization time is best in the fish ponds before the 5 ~ 7 days; (3) after the fish ponds spilled soy milk every day (each mu with 1 to 1.5 kg of soybean milk); and according to the color, every other 3 to 5 days of application of manure as top dressing, so that the transparency of the pool to maintain 25 to 30 cm. 6, management is less scientific. Fertilizer, soy milk spilled unevenly, resulting in water quality is too thick or too thin, and it is unfavorable to the breeding of palatability food organisms (rotifers and leeches). In the event of sudden changes in the weather, it is easy to cause the floating head of the fry to die; followed by water injection time is too long or note If the amount of water is too large, the top flow of fish will consume a lot of physical strength for a long time. These are the factors that cause the fry cultivation effect to be unsatisfactory, and should be paid attention to in production. 7. When the long-distance transport of fish fry the pond, due to improper handling, it will lead to a large number of deaths, or even all dead. The reason for this is that in addition to the “regulating temperature” work, the water quality indicators contained in the seedling bag will change greatly due to changes in temperature and decomposition of the excreta, and sometimes the fish poisoning will become subconscious. The state, if it is not dealt with at the time of release, may result in a large number of deaths. The solution is to first load the seedling bag in the shade of the fry pool and float it for 1 to 2 hours to balance the water temperature, and open the bag until the temperature difference between the water temperature inside and outside the bag does not exceed 2°C. After the fry bag is opened, the fry can not be put into the fish pond immediately, but a small amount of water should be gradually added to the bag to mix with it to balance the water chemistry index. Pour the fry into large plastic basins and gradually add pool water to the basin to better balance water chemistry. Observe the behaviour of the fry until they are fully functional before putting them into the fish pond. 8, fish quality is too poor. Fertility of broodstock or inbreeding fry due to congenitally less vitality, the survival rate of cultivation is often not high, and the individual size is uneven, the proportion of malformed seedlings accounted for a large proportion; some fry breeding grounds of poor hatch conditions, unclean utensils, The fry produced has more pathogens (such as pathogens, parasites, etc.) or is contaminated by heavy metals. The survival rate of the fry after hatching must be very low; the seedlings produced in the high temperature season have very short incubation time and the vitality of fry is relatively fragile. The survival rate at the time of breeding is also generally low. In addition, because the fry is too tender, the sinking sinks behind the pool and it is also prone to massive deaths. The survival rate after the same batch of fry after several times of “packaging, shipping, putting in the pond” is not necessarily high.

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