Exclusive report of Teng's Aquatic Products Business Network:
Author | Luo Minhui Guangdong Haida Group
About author:Luo Minhui, graduated from the College of Fisheries of Huazhong Agricultural University in 1997, has been engaged in feed sales and breeding technology research and development, Guangdong Haida Group aquatic products senior service expert, contact email: [email protected].
In recent years, it has become apparent that grass carp is becoming more and more difficult to raise. The incidence of grass carp in central China is becoming more and more serious, and the average survival rate has now dropped to about 60%, with the lowest 20% less than 20%.
This year's losses have been even worse, the peak season has not yet arrived, and the mortality rate in many ponds has exceeded 30%, and some farmers have to re-seed. Judging from our survey data, the overall loss is not less than 10%.
Picture 1 Stacks of medicine bottles
Picture 2 Baby grass carp who died prematurely
First, there are many reasons for the high mortality rate of small grass carp, and the loss is heavy before the peak period, and the back is not optimistic
Why the survival rate of small grass carp in Hubei has continued to decline in recent years, most experts believe that there are three points: (1) the density of culture continues to increase; (2) the climate and pond conditions have deteriorated; (3) the resistance of fry has declined; from these three points, this year's fish disease is not optimistic.
The time has entered the middle of April, the first wave of fish diseases has begun, how to do a good job in prevention and treatment, there is no time to delay.
Second, prevention is difficult, and several common phenomena are worth thinking about
(1) Why is the peak incidence of grass carp old three diseases always in early April to mid-June every year, and after mid-June, the old three diseases of small grass carp rarely occur on a large scale, why?
(2) Wave after wave, basically 3-4 waves per year, one wave is more serious than one wave, and one wave is more difficult to treat than one wave, why?
(3) Different ponds, even if the pond mouth is next to the pond mouth, the time of onset is not very consistent; in the same pond, not all fish are sick at the same time, microscopic examination of fish in the same pond, parasites are different, why?
(4) The insect is killed, the poison is eliminated, and the detoxification is changed to the bottom, why can't it be prevented?
(5) Hepatobiliary syndrome? Judging from our survey data in recent years, it is rare to stop feeding and cure fish diseases in April and May, and the bait rate is lower than 0.5% of ponds, and the mortality rate is higher than that of 1.0-1.5%.
Third, the three-ring principle of fish disease prevention and control tells us that we must help fish and combat and control pathogenic factors
Fish disease, whether it is prevention or treatment, the overall idea can not escape the principle of the three rings.
Picture 3 The three-ring principle of fish diseases
Table 1 Classification of common grass carp species diseases in Hubei
Whether the fish will develop disease is the result of the joint use of three factors of the water environment, the resistance of the fish body, and the pathogen, and these three factors affect each other.
There are many causes of fish disease, some of which are listed in Table 1, and there are many diseases with basically the same treatment regimen that are not listed. Many situations often occur simultaneously in production, and it is difficult to develop effective prevention and treatment programmes based on experience alone.
Whether it is disease prevention or treatment, the starting point is actually the same, helping fish, combating and controlling pathogenic factors. That is to say, we must consider the three factors of fish body, water body and pathogenic factor at the same time.
Our fish have no problems, whether our water is normal, the pathogenic factors are not very active, let's analyze them one by one.
Fourth, whether there are dead fish in the pond cannot be used as a criterion for judging whether the fish are sick or not
Whether the fish in the pond are sick or not involves the first problem of judging standards, and the second is the level of judgment. The most common criterion in production is whether there are dead fish, right, definitely not.
Just like the new crown pneumonia outbreak in the world, there are completely healthy people, latent infections, mildly infected people, severe patients, and super severe patients. Only severe patients and super severe patients are life-threatening, can we say that latent infections and mildly infected people are not sick?
Fish diseases are actually the same way, and there will be different severity. All fish have three lines of defense against disease, and only if all three lines of defense are breached will dead fish appear.
I divided the gills of grass carp into four grades 5 years ago, and the treatment options at different levels are completely different. How to grade, how to check, how to deal with, I will write a few articles to discuss with you.
Table 2 Three lines of defense against disease in fish
Since March this year, we have done a lot of testing. The detection rate of wheelworm is more than 70%, and the detection rate of wheelworm disease is more than 40%. Gill filaments, intestines, and livers often have problems of varying degrees.
That is to say, our fish, all three lines of defense have problems, as the water temperature continues to rise, bacteria, parasites and fungi multiply faster, if we do not intervene in time, what will be the result?
Fig. 4 Mild inflammation of the intestine
Fig. 5 There are many ciliates with abnormal gill filament structure
Water is a problematic water, the root of disease, the hell of fish
From February to mid-June, it is the peak period for abnormal water quality. Our analysis is mainly related to two factors, one is the climate, and the other is the pond water quality management scheme at this stage.
Figure 6 Census of Ezhou Governor's Agricultural Water Quality (April 2018)
Figure 7 Turbid water due to different causes
From the beginning of April to mid-June, it is one of the two most intense periods of climate change in central China. The temperature difference between morning and evening is large, and the daily temperature change of more than 10 degrees is the norm, and there are often cold snaps.
The impact of drastic changes in temperature on water quality is mainly reflected in two aspects, the heating on sunny days is easy to induce bubble disease; the cooling leads to a large amount of organic matter floating at the bottom of the pool, which is prone to lack of oxygen or inverted algae in the water.
The influence on pathogens, the underlying organic matter and bacteria, eggs, mold spores, etc. float together, bringing convenience to the reproduction, movement and invasion of fish bodies of pathogens.
The peak breeding period of pathogens is from mid-March to mid-June, especially from mid-April to mid-June. The number of Aeromonas hydrophilus we monitored often reached more than 5000/ml. After mid-June, the number will drop rapidly.
Fig. 8 Erosion of fins
Figure 9 Culprits
The impact on the fish body is that it is easy to lack oxygen (often not directly related to the amount of ponds), the second is a strong stress response, and the third is that pathogens invade more easily. It is easy to erupt bubble disease on sunny days and oxygen deficiency on rainy days.
The continuous impact of up to 3 months is a serious test for fish and water, and the fish body itself has not recovered before the peak of death, and once the dead fish begin to appear, the problem is often very serious.
Sixth, the prevention and treatment of diseases need to consider four issues at the same time:
Whether it is prevention or treatment, four issues need to be considered at the same time: (1) killing or controlling existing pathogens in fish, including parasites, pathogenic bacteria, fungi, etc.; (2) controlling existing pathogenic factors in water (not just bacteria, parasites) ;(3) rapidly recovering and maintaining the resistance of fish bodies; (4) continuously controlling the reproductive rate of pathogens in water and reducing the impact of non-pathogenic factors such as stress.
1. How to control the number of existing pathogens in fish, including bacteria, fungi and parasites.
Fish that already have mild inflammation (more than 80% of the pond mouths we have detected) must be treated by taking antimicrobial drugs internally before repairing the intestinal dysbacteriosis caused by antibiotics. While taking antibiotics internally, we should pay attention to adding health care drugs with liver and pancreatic repair functions.
For fungi and parasites, they can only be controlled by water administration at present.
2. How to reduce the number of pathogen outbreaks
As of March 21, the measured water temperature in many places in Hubei has exceeded 18 degrees for 5 consecutive days, and our technical service personnel have also detected a large number of parasites in Tangtou, so we issued the first insecticidal and sterilization notice on March 21.
How to do insecticidal sterilization in the end, in order to effectively reduce the occurrence of diseases behind, we have two sets of programs, called two worms and two bacteria program and three worms and three bacteria program, the main difference is the time of the first insecticide.
The two-worm and two-bacteria scheme needs to start at a water temperature of about 18 degrees, kill insects on the first day, and sterilize on the second day; do the second insecticide and the second sterilization about 10 days apart.
If the water temperature reaches more than 24 degrees before the first insecticide begins, the three-worm and three-bacteria scheme needs to be used. The first day of insecticide, the second day of sterilization, the 8th and 15th days of each killing insects, the 9th and 16th days of each sterilization.
Based on the occurrence of parasites and the experience of medication over the years, the first insecticide needs to consider three kinds of insects at the same time: wheelworms, ringworms, and anchor fleas, and it is best to use several drugs to compound, you can consult pharmacies; the second and third insecticidals only need to consider anchor fleas. The premise is that after sterilization, the water quality substrate should be adjusted, otherwise the wheel worm ring worm will occur more often.
For water mold and gill mold, it is best to check with a microscope. If so, it is possible to use 1-2 times after each water quality adjustment with drugs for the treatment of mycosis.
3. How to quickly recover and continue to maintain the resistance of the fish
Improving the resistance of the fish body is actually to restore the three lines of defense against diseases in the fish body.
Whether it is to restore the mucus on the surface of the fish or to restore the damaged organs, it is first necessary to have a certain amount of high-quality protein supplementation. At this time, the choice of feed is crucial, because the fish's intestines, liver and pancreas and other digestive organs have not yet recovered, and the feed or high-protein feed made of ordinary raw materials or a large number of feedings will only cause indigestion, not only can not achieve the purpose of recovery, but will aggravate the condition of the fish.
Table 3 Feed selection and feeding at different stages
4. How to continuously control the reproductive rate of pathogens in water and reduce the influence of non-pathogenic factors such as hypoxia and stress response
Aquatic organic matter is one of the main reasons for the large number of pathogens, and the decomposition and utilization of organic matter must be strengthened.
The research of many experts and our production data over the years have proved that regular detoxification and bottom modification, fertilization and bacterial replenishment are very important, which can effectively control the reproductive rate of pathogens (mainly protozoa, harmful bacteria, fungi) and reduce the risk of bubble disease, stress response and hypoxia in fish.
For bubble disease, it is not entirely the cause of water quality overweight, and the most effective and easiest and cheapest solution at present is to open an aerator at noon on a sunny day.
In order to achieve the effect of prevention, there are four places that need to be paid attention to:
1. The plan should be:
Every issue must be considered, or it will fall short. Several factors that contribute to the onset of grass carp last from early March to mid-June, and it is necessary to use it regularly.
2, the product should be true:
Feed or animal protection products, each manufacturer advertises that their products are the best. In particular, animal protection products, the description is written perfectly, any problem can be solved, you need to learn some simple identification methods. Lots online.
It must be noted that fake products = ineffective = dead fish loss + upset + cost + labor + delay the best time for prevention and treatment.
3. The dosage should be accurate:
Water body medication is basically not a big problem, the dosage of internal medication, there are still many people according to the feed to calculate the dosage, completely wrong.
Whether the internal medication has an effect or not, the most important thing is to achieve a certain drug concentration in the blood of the fish body. Whether it is a bactericidal drug or an immune enhancer, in addition to the quality of the drug, the amount of medication must be calculated according to the weight of the fish eaten in the pond.
4. The timing should be accurate:
Whether it is feed or animal protection products, there is the most suitable time to use. You can't wait until the problem is serious and then remediate it.
Feed, a product clearance has been proven to be inappropriate. This is especially true for animal protection products, different seasons, different pond conditions, different stocking models and feeding management schemes, the problems that need to be solved are completely different, and the schemes are naturally different.
Limited by the length of the article and the level of the author, i have talked about a lot of problems, but also left a lot of suspense, I will write out the problems that are not explained in detail as soon as possible for your reference.
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