Today's cold dew, the temperature difference between day and night increases after late autumn, what diseases should aquaculture pay attention to?

October will enter the "cold dew" and "frost" festival, the temperature gradually drops everywhere, the temperature difference between day and night increases significantly, the pond water quality gradually ages, and it is easy to induce fungal and parasitic diseases of aquatic animals. Aquaculture has also entered the harvest season, and fish, shrimp and crabs have been caught and marketed. The northern region has entered the preparatory stage before wintering, and it is necessary to pay attention to the intensive cultivation of overwintering seedlings; most of the southern region is still a good growth period for breeding species, and when catching and pulling nets, we must pay attention to the impact on the breeding objects to avoid diseases caused by mechanical damage.

First, the diagnosis of the disease

(i) Fish diseases

1. Grass carp hemorrhagic disease: it is a disease caused by aquatic reovirus, which mainly endangers grass carp fingerlings. When the water quality deteriorates, the dissolved oxygen in the water is low, the transparency is low, the oxygen consumption rate of total nitrogen, organic nitrogen, nitrite nitrogen and organic matter in the water is high, the water temperature changes greatly, and the resistance of the fish body is low, which is easy to make grass carp hemorrhagic disease epidemic. The water temperature of the disease is 20 °C ~ 30 °C, and 25 °C ~ 28 °C is the most likely to occur. The main grassland carp rearing areas need to focus on prevention and control.

2, freshwater fish bacterial sepsis: can infect most freshwater fish, with the disease course of rapid, high mortality characteristics, especially the water temperature continues to be above 28 °C, after the high temperature season the water temperature is still maintained above 25 °C when the incidence is high, the disease can be transmitted through sick fish, bacteria pollution of bait, utensils and water sources, birds prey on diseased fish can also cause the spread of diseases between different breeding ponds, the country's freshwater fish farming areas need to focus on prevention and control.

3. Bacterial enteritis disease: it is a high incidence of grass carp and bluefish, which can occur from fish species to adult fish, and carp and bighead carp also have a small number of occurrences of this disease. The water temperature above 18 °C began to circulate, and 25 to 30 °C is the peak of the epidemic, often complicated with bacterial gill rot disease, erythroderma, etc., resulting in a higher mortality rate. All grass carp and bluefish breeding areas need to focus on prevention and control.

4. Catfish intestinal sepsis: a disease caused by Eduardella catfish infection, the main object of the disease is spotted catfish, due to differences in catfish size and individual immunity, the clinical symptoms of the disease show acute and chronic forms. High mortality of the acute type, manifested mainly by sepsis and enteritis; The chronic type is characterized by "head piercing". The disease can occur from seed to adult fish, and the epidemic time is long, and the water temperature of the disease is 24 to 28 °C. Anhui, Jiangxi, Hubei, Hunan, Guangdong, Guangxi, Sichuan, Guizhou and other catfish production areas need to focus on prevention and control.

5, wheel worm disease: is a large number of, a variety of wheel worm parasitized in the skin or gills of the fish body caused by the disease, mainly there are significant wheel worms, coarse spiny wheel worms, etc., is a more popular and harmful parasitic disease in China's fish farming production, fish farming areas throughout the country have occurred, in the continuous rainy weather to pay special attention to the outbreak of the disease.

6. Irritating cryptonuclear worm disease: it often parasitizes the skin of seawater telebony fish and the subpithelium of the gills, which can cause infectious diseases of fish. The main occurrence targets are yellow croaker, grouper, oval pomfret and so on. The suitable water temperature for stimulating cryptonuclear worm disease is about 25 °C, and the summer and autumn seasons are the high incidence periods of the disease, especially after the typhoon, the marine environment changes greatly, and the fish body resistance is poor. Fujian, Zhejiang, Guangdong, Hainan, Guangxi and other marine cage concentration areas need to focus on prevention and control.

(2) Shrimp diseases

1. Leukoplakia syndrome: the general water temperature is easy to erupt at 18 ~ 30 °C, and the main harm objects are Vannabin shrimp, Chinese shrimp, Japanese shrimp, etc., and the main coastal shrimp culture area needs to be key prevention and control. In addition, the main cultivation areas of Ke's original crawfish in Hubei, Jiangsu, Anhui, Jiangxi and other places also need to strengthen the prevention and control of the disease.

2. Shrimp intestinal bacterial disease: bacterial diseases caused by bacilli, mostly occur in the III stage of the larvae to the iii. stage of the bran shrimp larvae, the mortality rate is high, the diseased larvae swim slowly, the phototropism is poor, the serious ones sink to the bottom of the water, most of them die, and a small number of survivors are cured after developing into shrimp. Sometimes the disease begins early from the second stage of the flea larvae, and some are still sick in the shrimp stage.

(3) Crab diseases

River crab enteritis: it is a common and frequent disease in river crab farming, especially in the rainy or high temperature season. The main causes of the disease are the deterioration of water quality, the deterioration of the substrate, and the lack of fresh food fed. All river crab farming areas need to pay attention to the prevention and control of the occurrence of this disease.

(4) Shellfish diseases

Abbacillus pustular disease: a kind of bacterial enteritis disease caused by infection with Vibrio, in the early stage of the disease, the disease of abalone slow movement, reduced feeding, crawling from the back of the grow-out plate to the surface of the grow-out plate or the wall of the breeding pond. The surface color of the gastropod muscles is lighter, and as the disease worsens, the color of the gastropod muscles becomes pale and white, and a number of white pustate pustules appear, and after the pustules rupture, a pore-like wound 2 to 5 mm deep is formed. There is pus flowing out, followed by ulceration and necrosis of the wound muscles. In the later stage, the disease abalone stopped eating, the abdominal foot muscle adhesion was significantly weakened and the ulcer was large, and finally died, with a mortality rate of 50%.

(5) Other diseases

Turtle ulcer disease: the disease is caused by a variety of bacterial infections such as aerophilic bacteria, mild aeromonas, Pseudomonas and colorless bacilli, and the water temperature above 20 ° C is prone to illness and epidemic, the higher the temperature, the higher the incidence. Sick turtles fester everywhere on the surface of the body, and can rot to the bones, juvenile turtles and close relatives can be harmed, often causing a large number of deaths of juvenile turtles and young turtles. After adult turtles and turtles fall ill, they often have a longer course of illness. When the environment improves and is treated, the ulcer can form a scab and heal. The disease can occur in turtle-raising areas throughout the country,

In addition, freshwater fish generally farmed also need to pay attention to the prevention and control of gill disease, erythroderma, hepatobiliary syndrome, anchorhead loach disease and ringworm disease. Tilapia needs to pay attention to the prevention and control of streptococcal disease and Luohu virus disease. Shrimp need to pay attention to the prevention and control of gill rot and vibriosis. Crabs pay attention to the prevention and control of molting failure.

2. Prevention and control measures

Entering October, after several months of bait, fertilization, medicine, etc., the water environment has undergone great changes, the light has been relatively reduced, and the pond load at this time has reached a high level, and it is necessary to pay attention to strengthening the management of the following aspects.

(1) Strengthen water quality management and improve the ecological environment.

1. Control water quality. The dissolved oxygen is maintained at more than 5 mg/L, the pH value is 7.5 to 8.5, the transparency is maintained at 30 to 40 cm, and the indicators such as ammonia nitrogen, nitrite, and hydrogen sulfide are controlled within the appropriate range.

2, to timely water into the pond, change water. If the water quality of the outer river water source is better, it can be regularly (10 to 15 days) to change the water once, about 20 centimeters each time; if the water quality of the water source is poor, you can choose sunny weather, inject water every 15 to 20 days, and use compound microbial agents to adjust the water quality, pay attention to the use of microbial preparations, do not use disinfectant fungicides immediately, in order to prevent killing beneficial bacteria and affecting the water quality effect of biological agents.

3, to use the aeration equipment in a timely manner. Depending on the weather conditions, the aerator or pump is turned on at different times. Adhere to the principle of opening at noon on sunny days and not opening in the evening; opening in the early morning on cloudy days and not opening during the day; opening before floating heads and opening in the middle of the night on continuous rainy days. At the same time, prepare first-aid chemical oxygenators to prevent hypoxic floating heads.

(2) Strengthen fertilization management to ensure growth and preservation.

The average temperature in October is still maintained above 22 °C, which is the peak season for fish growth, and fertilizer input cannot be relaxed, which can not only provide sufficient natural food for fish growth, but also preserve fattening and lay the foundation for fish to overwinter smoothly.

(3) Strengthen feeding management and enhance the disease resistance of fish bodies.

It is necessary to implement the "four certainties" bait principle of "timing, positioning, quality, and quantity." The amount of bait thrown should be flexibly controlled according to the weather, water quality and fish feeding. The bait should be nutritious, palatable, fresh and non-deteriorating, and ensure that the fish are full and well eaten and not wasted, so as not to pollute the water quality.

(4) Strengthen disease prevention and control, control and eliminate pathogens.

Autumn fever may become another peak period for fish disease, and it is necessary to focus on prevention and combine prevention and control. For water disinfection, whole ponds such as bacterial poison double killing, chlorine dioxide, bacterial poison extermination or bromochloroheine can be used to kill pathogenic bacteria in the water. According to the water quality, the quicklime can be applied appropriately to adjust the phH value.