Tilapia still die in large numbers in winter to prevent and cure nutritional diseases of tilapia.

Tilapia is a tropical fish, the suitable temperature for its growth is 25 ~ 35 ℃, and the lethal temperature below 10 ℃ is the lethal temperature, but the phenomenon that the water temperature in the south of China drops to the lethal temperature of tilapia is very rare, which provides favorable conditions for tilapia to survive the winter safely under natural conditions. In winter, however, large-scale disease and death of tilapia occur in many places. The following is to discuss the causes of disease and death of tilapia, and put forward prevention and control measures for reference.

Tilapia culture

1. Occurrence and symptoms of fish disease:

In winter, the death of tilapia mostly occurred two or three days after the sudden drop in temperature, when the temperature rebounded, the loss varied greatly, with a large number of concentrated deaths and continuous deaths for several consecutive days. Examination of diseased fish, the appearance can be seen: fish body color is dull, lack of luster, thin body; exophthalmos, eyeball lens turbidity, whitening; abdominal enlargement, hyperemia of epidermis. However, there were no abnormal symptoms in fin and Gill and no parasites on the body surface. Anatomical examination: the fish was filled with water in the abdomen; there were pathological changes in the liver, mostly yellow, light yellow, and swelling and fat mass. It can be preliminarily determined that tilapia has a bacterial disease or nutritional disease.

2. Cause of death:

Changes in water temperature, salinity, dissolved oxygen and other environmental changes will more or less have adverse stimulation to tilapia. When vitamin A, E, B1, B2 and zinc are deficient in the feed, fish disease is easy to be induced, and the symptoms are similar to the above symptoms, which can be identified as nutritional diseases. During the discussion, it was found that at the lower limit of survival temperature, although tilapia did not die immediately, its activity was slow and basically stopped feeding. Therefore, there are few vitamins and trace elements in fish. When the weather becomes warmer, tilapia activities tend to be active, but the nutrients in the body can not meet the needs of activities, and the pathogens are also active with the increase of temperature. tilapia due to lack of nutrition and liver and kidney damage, fish immunity decreased, easy to be infected with pathogens, causing tilapia disease and death. Therefore, the decrease of the accumulation of nutrients, especially vitamins and inorganic salts, is an important cause of tilapia death in winter.

3. Prevention and control methods:

1. Nutritional improvement:

The use of full-price formula feed can ensure the comprehensive nutrition intake of fish, so that the accumulation of vitamins and inorganic salts in fish can meet the needs of activities. In this way, even if the temperature drops and affects the food intake of the fish, the fish can survive the winter smoothly with sufficient nutrients in the fish. In addition, some data show that during the overwintering period, the demand for protein of tilapia is not much different from that of normal culture, but the demand for fat and vitamins is greater than that of normal culture, so about 1% fish oil or vegetable oil should be added to the feed one month before overwintering. At the same time, timely add high-quality "multivitamin" to increase fish body fat and vitamin accumulation, which is conducive to overwintering.

Feed

two。 Disease prevention and treatment:

Tilapia is easy to be invaded by pathogenic bacteria because of malnutrition and other diseases such as water mildew and canker (caused by Pseudomonas hydrophila). In addition, in the low temperature environment, it is also easy to be parasitized by parasites such as melon disease, oblique tube disease, rotifer disease and so on. Therefore, the water body must be disinfected regularly to keep the water fresh and prevent diseases. Commonly used water disinfectants are quicklime, "strong chlorine", copper sulfate, ferrous sulfate mixture (5 ∶ 2). For pond culture, the whole pond was sprinkled with disinfection at doses of 200ppm, 0.3ppm and 0.7ppm, respectively. Use one every 10 days and use it in rotation. In addition, water mildew is easy to be prevalent when the water temperature is lower than 15 ℃. Timely prevention and control measures should be taken, dead tilapia should be removed in time, and chemical control should be applied at the same time. Salt and baking soda mixture (1 ∶ 1) should be sprinkled in the whole pool at the dosage of 0.2ppm and 4ppm. For cage culture, hanging bottles, bags and baskets are used to prevent and cure fish diseases. The drugs used were bleach powder or the mixture of copper sulfate and ferrous sulfate (5 ∶ 2). Generally, each cage hangs 3 bottles (bags or baskets) every day, each loading 100g to 150g, twice a month for 2 consecutive days, using in rotation. In addition, we should pay attention to increasing oxygen in winter and turn on the aerator regularly to keep the dissolved oxygen in the water above 4 mg / L. If there is no oxygen-increasing machinery, manual water mixing or water injection, water exchange and other measures can be used to increase oxygen.