NO.1 Characteristics of spring water environment

The outbreak of aquatic animal diseases is closely related to the water environment in which it is located.

In the main fish-producing areas across the country, the characteristics of the water environment in spring mainly include the following aspects:

1. Rising temperature

North of the Huaihe River in the Qinling Mountains In the main fishery producing area, after March, the water surface of the culture gradually melted; at the same time, the water temperature in the southern region also gradually recovered, from the original 5-6℃ to 10-15℃;

The water temperature continued to rise. , causing changes in the ecological environment of aquaculture water bodies, and also having a direct impact on the outbreak of subsequent fish diseases.

2. The water temperature and air temperature remain unstable

In spring, in The main fishery producing areas in my country, except South China, have frequent cold air activities until May;

The water temperature in the pond continues to be unstable, and the stress response of fish is large. This is the case for fish after the beginning of spring. A direct cause of outbreaks of disease and mass deaths.

3. The temperature difference between day and night in aquaculture water bodies is large

In spring, in most of the main fishery producing areas in my country, especially in mountainous ponds, the temperature difference between day and night is very large. Sometimes the temperature difference between day and night even reaches 15 ℃, causing the water temperature to change even up to 5 ℃ within a day;

The drastic changes in water temperature cause the fish to have a relatively strong stress response.

At the same time, the temperature difference between day and night is too large, which also causes the formation of relatively strong density currents in the upper and lower layers of the water body, and the residual bait and feces deposited at the bottom of the pond appear;

This also brings about the The deterioration of the environment and the growth of pathogenic bacteria have had a relatively large impact on bottom fish, and are also an inducement for the frequent occurrence of fish diseases after the beginning of spring.

4. Frequent rainy weather

For most of my country's main fishery producing areas, there is relatively much rain from March to May in spring, and during Qingming and Grain Rain seasons, there is usually a lot of rain. Along with the rain, sometimes even continuous rain.

Unstable weather and the relatively weak physique of fish after overwintering. These factors add up to each other and easily lead to frequent fish diseases after overwintering.

NO.2 Major Fish Disease Outbreaks

Every March to May is the peak period for fish disease outbreaks in the main fishery production areas, especially in old fish ponds that overwinter every other year. Obvious;

In ponds where the onset of disease is urgent, the loss rate is high, and the disease is serious, the loss during the entire disease process may reach 70%-80% (as shown in Figure 1), which has brought huge economic losses to farmers. .

The main categories of fish disease outbreaks are as follows:

Secondary bacterial infection

Especially in recent years, fish after overwintering are often seen. For example, grass carp (grass carp after overwintering in central China is particularly common in recent years, as shown in Figure 4)

The red spots have no obvious pattern, and can be seen on the head, trunk, tail, etc., often accompanied by bacteria Sexual infection, pathogen isolation can isolate the dominant bacteria;

It is the most common disease with the highest loss rate after winter in recent years. Farmers call it "fish plague"!

It may be due to physical constitution. After doing a drug sensitivity test, it was found that oral administration of sensitive antibiotics was not effective.

In addition, forktail catfish encrusting disease is also a fish disease with a high incidence rate in spring (as shown in Figure 5). The main reason is that the amount of feeding in winter is very small or no feeding.

If the feeding time is too long, the fish's physique will decline, and the intestinal digestive function will weaken. In addition, intestinal health care is not in place after the beginning of spring. Feeding is too fast, and the intestinal digestive capacity cannot keep up. After the function becomes disordered, This induces intussusception.

Saprolegnia

In the early spring stage, due to the poor physical condition of the fish after overwintering and the drastic changes in the environment, the fish developed a relatively strong stress response;

Or due to physical reasons, the subcutaneous tissue is ulcerated and inflamed, and the tissue necrosis leads to saprolegnia parasitism.

This situation is more common in special aquatic species such as bass (Figure 6) in recent years after overwintering.

Parasitic diseases are common

In spring, as the water temperature gradually rises, the parasite eggs begin to germinate after a winter of relative inactivity;

This At this time, parasitic diseases enter a stage with a relatively high incidence rate, especially when the water temperature is 15℃-25℃. The water temperature at this stage is most suitable for the growth of parasites;

The more common parasites are In particular, some fish with relatively poor physical constitution have weak ability to clear parasites, such as trichozoa, small melon worms (as shown in Figure 7), and ringworms, and are easily parasitized by parasites.

Some parasites can also cause fatal harm to certain species. For example, tubeworm can cause massive losses in mandarin fish.

Air bubble disease

In the early spring stage, the water temperature of the water body gradually increases, the light begins to gradually increase, and photosynthesis begins to gradually increase;

When the weather is fine for several consecutive days , the dissolved oxygen in the pond water is prone to oversaturation;

Due to the sharp rise in water temperature, the solubility decreases, and the dissolved gases in the fish blood will escape and condense into tiny bubbles;

However, due to the oversaturation of dissolved oxygen in the outside world, the gas in the body cannot be easily discharged quickly, and a gas embolism will form in the body, which is also known as bubble disease.

It is especially common in water flowers and early seedlings where the body's regulatory ability is relatively weak.

NO.4 The main reasons for the high incidence of fish diseases in spring.

1. The water environment continues to be unstable and fish have a large stress response, which is an environmental factor that induces the disease in fish after overwintering.

2. Fish health care is neglected before wintering.

After a small amount of feeding or even stopping feeding during the overwintering period, the fish's physical condition declined;

After feeding started in spring, oral health care did not keep up with it in time, and in recent years, the feed Decreased quality, extensive use of alternative raw materials, and poor physical fitness are the direct reasons for the high incidence of fish diseases.