Tilapia fry water quality management technology, tilapia has a wide range of feeding habits, hypoxia tolerance, fast growth, less disease incidence, strong reproductive capacity and other advantages, and easy to feed, good market. At present, it is widely cultivated in China, and it is the main breed to increase the income of many local farmers and aquaculture units. Especially, tilapia is more active in the international market, so intensive cultivation is in the ascendant. However, intensive farming has gradually brought about some problems. Many farmers, due to one-sided pursuit of production, constantly put too much feed and fertilizer into the aquaculture water body, so that the water quality continues to deteriorate. When the living environment of fish exceeds the standard, a large number of dead fish and market barriers due to health problems often occur, which brings great losses to the aquaculture operators. At the same time, tilapia belongs to tropical fish, which has special requirements on the breeding environment and management, and relatively high requirements on water quality. Therefore, water quality management has become the key to the success or failure of tilapia culture.
1、 Careful selection of water sources
Tilapia is a kind of tropical salty fish. It can grow at the temperature of 18 ℃ ~ 38 ℃. The most suitable temperature for growth is 28 ℃ ~ 32 ℃. It can still eat in water with dissolved oxygen less than 0.7 mg / L. it can grow and reproduce when dissolved oxygen in water is 1.6 mg / L. It can grow, develop and propagate in the fresh water, and can grow in the water with pH value of 4.5-10. In aquaculture, water source is the most basic and important aspect, which determines the water quality conditions and the success or failure of aquaculture. The general water source conditions require stable, sufficient, clean and sanitary water source, suitable water temperature, good water quality, no pollution, in line with the national fishery water quality standards, and at the same time, it is required that the water injection and drainage are convenient, and single injection and single discharge. Fish traps should be built at the water injection and drainage outlets to avoid harmful organisms and wild fish entering the pool, and to prevent fish escaping. The water source should be filtered and disinfected in the reservoir before it enters into the aquaculture pond to kill pathogens and harmful organisms in the water source. Generally, 25 g / m3 ~ 30 g / m3 quicklime or 1 g / m3 bleaching powder (containing more than 25% effective chlorine) can be sprayed in the whole pond. When it is necessary to kill and kill insects, it can also be sprayed with 0.5 g / m3 trichlorfon (90% crystal trichlorfon) in the whole pool. During cage culture, the water temperature must be between 18 ℃ and 38 ℃ all the year round. The water quality should meet the fishery water standard. The water source should be stable and free of pollution sources. In winter, there should be no ice sealing, the water surface should be open, the wind should be away from the sun, the light should be sufficient, and the environment should be quiet. There should be no industrial or agricultural polluted water flowing into the water source.
2、 Strictly clean and disinfect the pond
Disinfection of clear pond can kill pathogenic factors of water body and ensure good water quality conditions. The old and new ponds must be cleaned and disinfected before the seedlings are put in. Excessive silt should be removed from the old pond and only 10 cm of sediment should be retained. In order to kill pathogens and harmful organisms in the aquaculture water, the pond was disinfected with drugs 10-15 days before stocking. Generally, two methods can be used to clear the pond by dry method or with water. When the pond is cleaned by dry method, about 75kg quicklime or 4kg-5kg bleaching powder can be used per mu; when the pond is cleaned with water, about 150kg of quicklime can be used in the whole pond to mix the soil at the bottom of the pool with quicklime as much as possible, so as to completely kill parasites, pathogens and wild fish. The method of hanging medicine bags can be used to disinfect the cage culture, and the new cage should be fully soaked and disinfected before going into the water.
3、 Scientific fertilization and feeding
The amount of fertilizer, bait and other inputs not only affect the growth of tilapia, but also affect the change of water quality. Tilapia does not have strict requirements on water quality. In natural waters, the main feeding objects are benthos, aquatic insects, zooplankton, rotifers, organic debris and large algae. It can absorb plankton in the water as food, especially for artificial feed. In aquaculture, we can also make the plankton in a good growth state, increase dissolved oxygen and nutrients in the water, maintain good water quality, and assist fish growth. In general, before the fish species are released, sufficient base fertilizer can be applied to improve the nutrient status of the sediment in the water body and increase the nutrients in the pond, which is conducive to the growth of natural bait. The specific method is to apply 250-300 kg rotten chicken manure per mu. In the middle stage of cultivation, topdressing can also be applied according to the water quality in the water body. Generally, it is better to apply topdressing once every 15-20 days. Each time, 2kg-3kg of nitrogen fertilizer and 1kg of phosphate fertilizer can be applied per mu. A small amount of Azolla or Azolla can be put into the pool, and organic fertilizer or biological fertilizer can be applied according to the water temperature and water quality. Tilapia is one of the main objects of current high-density aquaculture or "factory" aquaculture. Intensive aquaculture needs to feed comprehensive formulated feed. However, if we do not grasp the scientific method in feeding, it will not only waste feed, but also damage the water quality and induce various diseases. Therefore, the feeding of tilapia should be scientific. Tilapia has a wide range of feeding habits. Under the condition of artificial feeding, it can be fed with various kinds of feed, such as wheat, corn, cake, etc. The protein content in the initial feed should be 32% - 35%, and the daily feed amount should be 3% - 5% of the total weight of fish. When the individual size is about 200g, the feeding rate can be adjusted to 2% of the total body weight of the fish, and the protein content in the feed can be kept at 27% - 29%. When the individual reached about 300 g, tilapia entered the fastest growth period. The daily feeding amount was kept at 1% - 2% of the fish weight, and the protein content in the feed was more than 35%. The feed can be mixed by itself, but it is better to be processed into granules for feeding. The principle of "four fixed" should be emphasized in feeding method. They were fed twice a day from 8:00 to 9:00 a.m. and from 3:00 p.m