Overwintering techniques of Freshwater White Pomfret fry

Freshwater Pomfret is a freshwater farmed fish species introduced into mainland China in the 1980s. It is deeply liked by the majority of farmers because of its good meat quality, fast growth, easy management and large market sales. However, because Pomfret is a warm water fish, the suitable temperature for growth is 15 ℃ 30 ℃. When the water temperature is lower than 12 ℃ or higher than 36 ℃, it will freeze to death or burn. Therefore, freshwater Pomfret fry overwintering should grasp the following technical points.

First, the choice of venue. The pond that chooses freshwater Pomfret to overwintering must be able to maintain a water depth of more than 1.5m, a minimum water temperature (January) of more than 12 ℃, an area of 1000mur2000 square meters, convenient water sources, plenty of sunshine, and the best place to avoid the north wind.

Second, the installation of cold shelter. Ordinary ponds (ponds without hot spring water) and freshwater Pomfret overwintering must be equipped with cold shelters. At present, most farmers use small galvanized tubes with angle iron welding to make a half-moon shape, fixed on the pond embankment, and then cover the shelves with nylon film. The location of the construction is generally in the north-south direction of the pond near the north, and the shed area accounts for about 1max 2 or 2max 3 of the whole pond. Straw or weeds can also be used to form a 100 × 130 cm piece of grass, and then the grass can be covered on the surface of the fish pond in the north of the pond. The front end of the grass is 70 cm above the water surface, and the back end is close to the water surface. Put some straw under the cold shelter. In this way, when a cold wave strikes, fish fry can be clustered in the grass to keep warm. Some farmers keep floating lotus in the pond at 1x2 or 1x3, isolated with bamboo poles, so as not to let them grow arbitrarily in the whole pond. One of the above measures is to prevent hail or snowflakes from falling directly into fish ponds on rainy and snowy days, alarming schools of fish and causing them to be injured. Of course, there is no need to build cold shelters in ponds with hot spring water, and freshwater Pomfret can survive the winter safely.

Third, daily feeding and management. During the overwintering period of freshwater Pomfret (from late November to late February of the following year), whether the feeding and management is in place or not directly affects the survival rate and overall economic benefits of spring slices. Therefore, management should pay attention to:

1. Feed. When the water temperature is above 20 ℃, the daily feed dose should be controlled at 4% of the fish body weight and fed in the afternoon. Generally, peanut bran or feed containing more than 30% crude protein should be used after soaking. When the water temperature is about 15 ℃, daily feeding accounts for 2% of the fish's body weight, and it can be fed in the afternoon. It is not necessary to feed when the water temperature is lower than 15 ℃. The feed should be fed in the fixed position in the cold shelter at a fixed time, positioning, quality and quantity.

2. Water quality management. Due to the low temperature in winter, the metabolism in the pond is slow, so the water is easy to clear, often more than 30 cm transparency. At this time, some fermented chicken manure or pig manure should be properly put into the pond to make its water quality "green, tender and cool"; the transparency is about 20 cm.

3. Disease control. The main harms of freshwater Pomfret during overwintering are water mildew and melon disease, (1) water mildew. The disease is caused by mechanical injury or frostbite of the fish, the water mold zoospore invades the wound, absorbs nutrients from the skin of the fish and germinates and grows rapidly; one end of the hyphae is adsorbed in the skin tissue like a tree root, and most of the rest are exposed outside the body surface. The hyphae of water mold fluttered in the water in the shape of white cotton, which can be seen with the naked eye. Fish body parasitic water mold, will show restlessness, because the hyphae absorb the tissue nutrition in the fish epidermis, coupled with bacterial infection of the wound, so that the epidermis tissue necrosis, diseased fish gradually die because of emaciation. Prevention and treatment: clean the pond thoroughly with quicklime before ① fry is put in, which can reduce the occurrence of this disease. ② net fishing operation should be careful, so as not to hurt the fish, there are individual fish frostbite in cold winter, rain and snow, do not go into the pond to fish, interfere with fish schools. ③ can be sprinkled with 0.1ppm 's potassium permanganate solution throughout the pool, once every other day, twice in a row. (2) cucumber disease, also known as white spot disease. There are many small white spots on the body surface of the diseased fish, which can make the surface of the fish secrete a lot of mucus and form cysts in the parasitic place; if the pathogen is parasitic in the cornea, it can lead to blindness of the fish; the diseased fish show restlessness, and clusters swim around the edge of the pool; and constantly rub against or jump out of the water with other objects, the fish lose weight and become black, Gill filaments are congested, breathing is difficult, and soon a large number of fish die. The pathogen of small melon disease is many-bearing melon worm, which is suitable for the growth and development of water temperature of 15 ℃ and 25 min. Prevention and treatment methods: ① ponds should be thoroughly disinfected with quicklime, and cement ponds, glass containers, plastic containers and so on should also be disinfected with potassium permanganate or bleach powder. ② can be treated with dried pepper and dried ginger slices. 100g dried ginger slices can be used at a depth of 1m per mu of water, plus 500ml 1000g water, boil for 10 minutes, then cease fire for 20ml for 30 minutes; then, boil for another 10 minutes, then cease fire for half an hour; add 250g dried chili peppers and 2000 grams of water, and then boil for 10 minutes; finally, sprinkle 10kg of water with dregs and juice evenly throughout the pool, once a day for two consecutive days.

4. Other matters. During the overwintering period of freshwater Pomfret, try not to worry about the fish in the pond to avoid collision; it is strictly forbidden to use trichlorfon and other drugs; otherwise, the whole pond will die and the loss will be irreparable.

Fourth, management at the beginning of spring. When the water temperature is stable above 20 ℃, the appetite of freshwater Pomfret begins to increase, and concentrate feed and proper green feed should be fed at this time. The general concentrate feed is mainly peanut bran or soybean powder or compound feed containing more than 30% crude protein, and the daily feed intake accounts for about 4% of the fish body weight; the green feed is fed with forage or oil veined vegetables, which accounts for about 20% of the fish body weight; it is usually fed with green feed in the morning and concentrate in the afternoon. In addition, an appropriate amount of new water is injected into the pond to keep the water "green, tender and cool", which is beneficial to the growth and development of Pomfret fry and the sale and transportation of spring slices.