In feed production, any aspect of feed ingredients, production process, management, storage environment, etc., if unreasonable, may lead to the occurrence of moldy mildew in aquatic products. Moldy mycotoxins such as mycotoxins, CPA, ochratoxin, deoxygenated melon The vast majority of sterols, Fusarium toxins, etc. have been proven to cause harm to aquatic animals and even death. And mycotoxin has a synergistic effect, moldy feed generally contains a variety of mycotoxins, the harm of a variety of toxins is much greater than the harm alone. Mild fish feed will not only reduce its nutritional value, but also cause aquatic animal diseases. How mold has become the focus of research in the aquafeed industry. Mycotoxins are biological toxins produced by several molds such as Aspergillus and Penicillium, mainly aflatoxin, CPA, ochratoxin, deoxymuccum, Fusarium toxins, etc. About 200 kinds of mycotoxins have been Most of the known species are known to have serious damage to animals. Aflatoxin is very easy to contaminate corn, peanuts and cottonseeds and other components. With the feed source, more and more tend to use vegetable protein instead of fish meal and other expensive animal protein. The seriousness of mycotoxin contamination caused by the feeding of plant-derived feed, including its by-products, has greatly increased. There will be more mycotoxin contamination. The harmful effects of mildew on aquatic animals; how to prevent mildew in aquatic feeds; how to treat moldy feeds and the like have increasingly become the focus of the aquafeed industry.

1 Causes of mildew in aquatic feed
1.1 Raw Material Factors The water content of aqua feed raw materials is an important chemical index. If the water content is too low, it will be beneficial to storage, but it will increase the cost accordingly and reduce the economic benefit. If the water content is too high, it will cause mildew in the feed. If the compound feed is used without drying, the moisture content of the product is often exceeded and the product is susceptible to mildew. The moisture content of corn, wheat, rice, and other cereals as raw feed ingredients is 17% to 18%, which is the most suitable condition for mold growth. The crushed cereals are more prone to mildew when the moisture content is high. Therefore, the water content of aquafeed raw materials should be controlled below the safe moisture content, and the fish and shrimp feed should have a moisture content below 12%, and the carp feed moisture content should be below 9%.
1.2 Production factors When producing pellet feed for aquatic products, if the coolers and associated fans are improperly selected or improperly calibrated during use, the cooling time of pellet feeds is insufficient or the air volume is insufficient, resulting in excessive moisture content and temperature of the pelleted feeds. Such pellets are prone to mildew after bagging. The materials accumulated in the granule lifting hoppers and pipelines of the aquafeed pelletizing system can form moldy material if they are not periodically cleaned, and then enter the finished product warehouse and packaging bag after falling off, which can easily cause mildew in the entire batch of pellets.
The returned moldy material was improperly handled, and some used the elimination of zero return method. In this way, as the mold was not killed, it actually became a fungal inoculant produced by the next batch of materials, which expanded the pollution surface, accelerated the proliferation of mold, shortened the shelf life of the feed, and caused moldy and loss of large amounts of feed. In particular, fungi that cause mildew are mostly strains of toxin-producing bacteria, such as Aspergillus flavus, Aspergillus nidulans, etc. When the toxin exceeds a certain amount, it will affect the growth and development of aquatic animals, resulting in various diseases and even death.
1.3 Environmental factors The mold can use the protein in the feed as a nitrogen source under suitable conditions of temperature, humidity, and oxygen, and use fats and sugars as a carbon source for growth and reproduction. The main raw material in feed—vegetable raw materials—is contaminated with various molds and their conidia in the various stages from harvesting to processing and brought into the feed.
The growth and reproduction of mold depends on the proper moisture and temperature. Most of the mycotoxins belong to medium-temperature microorganisms, and the most suitable growth temperature is generally 20 to 30°C; and the optimum relative humidity is 80% to 90%. Therefore, the growth and reproduction of molds are closely related to regional climate conditions and seasons. In most parts of northern China, the average temperature in each month from May to September is above 20 °C, and the average relative humidity is above 80%. This season is the period of production and application of aquatic feed. Under this high temperature and high humidity environment, especially during the rainy season, mold growth is the most prosperous, and moldy fish feed mostly occurs during this period.
1.4 Management factors Raw material warehouses are not cleaned or contaminated for a long period of time. Materials accumulated in raw material warehouses (especially crushed ones) are prone to mildew; feed warehouses are wet, rodent damage is serious, and feed, infectious bacteria, and contaminated feed are easily contaminated; warehouse areas are not Frequent cleaning and regular disinfection, unreasonable feed stacking, long inventory time, and transportation of the feed by rain, exposure, etc., are easy to cause moldy feed.

2 Damage to Aquatic Animals from Mycotoxins in Feed
2.1 The hazards of aflatoxin Aflatoxin produced by Aspergillus flavus is the most harmful to aquatic animals, not only affects its growth, but also has carcinogenic effects.
Rainbow trout is one of the species most easily infected by mycotoxins in aquaculture species. Experiments have shown that the LD50 (maximum lethal dose) of aflatoxin is between 500 and 1000 ug/kg. Aflatoxin can cause rainbow trout fish gills to turn white, reduce the number of red blood cells, and damage the liver.
Oral 1 2 mg/kg (body weight) of aflatoxins in salmon can cause reflux of stomach contents. Aflatoxin entering the peritoneal membrane, if it exceeds 12 mg/kg, can cause hemoglobin levels to drop to 90% of normal levels, which can lead to necrosis of intestinal mucosa and blood cells. These cells can produce pancreas and stomach glands, making some organs lighter in color. These side effects in turn lead to slow growth of fish and poor feed performance.
Histopathological studies have found that mycotoxin B1 can cause hepatopancreas damage (crustacean). This damage can also cause other conditions, and mycotoxins in shrimp feed can affect yield. The Philippine scholars also found that when the mycotoxin concentration of shrimp feed was 73.8 ug/kg, the shrimp grew slowly and it was easier to get skin disease.
2.2 Hazards of CPA
Cyclopiasonic acid (CPA) is a toxin produced by Aspergillus and Penicillium. It is often found in the same sample as aflatoxin when it is warm, and even more common than aflatoxins. Aflatoxin slows fish growth and reduces red blood cell counts only at its highest concentration; CPA levels of 0.1 mg/kg produce the same hazards and, at higher concentrations, bring about digestive tract Necrosis. If 7.0 mg of CPA is injected per kg body weight of salmon, the fish will develop severe paralysis and die within 30 minutes.
2.3 The hazards of ochratoxin Ochratoxins are mainly toxins produced by Aspergillus and Penicillium and contain 7 structurally similar compounds. Among them, ochratoxin A is the most toxic, and ochratoxin A has kidney and liver toxicity. It often harms the kidneys of fish. And when it comes along with other toxins in the feed, it will reinforce other toxins. When people and animals ingest foods and feeds that are contaminated with this toxin, acute or chronic poisoning, teratogenicity, carcinogenesis, and mutagenesis can occur. The median lethal dose of oral ochratoxin on growing season rainbow trout is 4.7 mg/kg. The hazards to rainbow trout include liver necrosis, darkening of color, enlarged kidneys, and high mortality.
2.4 Decarboxylase Oxidation Decarboxylase is referred to as DON. It is often referred to as vomiting toxins, which are produced by the metabolism of Fusarium fungi. DON is a very important toxin in moldy wheat. DON in feed for rainbow trout was above 0.2 mg/kg. It will slow fish growth. When the feed concentration of rainbow trout reaches 20 mg/kg, antifeeding will occur.
The above are the hazards of common mycotoxins to aquatic animals. Under actual circumstances, mildewed feeds may contain more than one kind of mycotoxins. The mycotoxin has a synergistic effect, and the hazards of the two toxins combined are greater than the effects of the two alone.

3 Anti-mildew measures for aquafeed
3.1 Control of the quality of feed ingredients Raw materials should be checked on a package basis when entering raw materials, and the water content of raw materials must be strictly controlled. General requirements of corn, sorghum, rice and other water content should not exceed 14%; wheat, sub-powder, bran and other water content should not exceed l3%; bean seed cake, cotton seed cake, rapeseed cake, sunflower kernel The moisture content of cakes, pancakes, peanut cakes, fishmeal, bone meal and meat and bone meal should not exceed 12%.
3.2 Control of moisture and temperature during feed processing During the processing of aquafeed, it must be operated according to specifications, and after it is completely cooled, it can be bagged, transported and used. Even if the aquatic feed and raw materials meet the requirements for safe moisture, if the package is sealed, the moisture will cause mildew. According to experiments, the use of double-layer polyethylene film packaging feed products can effectively improve the waterproof effect. Under the conditions of a temperature of 5 to 32°C and a relative humidity of 40% to 75%, it can be stored for one year for the feeds that achieve safe moisture, and can be produced. The bacterial load of toxins, Aspergillus flavus, and Fusarium moniliforme gradually decreased.
3.3 Strengthen the management of storage, packaging and transportation of feed ingredients and products
3.3.1 Storage facilities The warehouse where feed is stored should be characterized by no leakage, no humidity, complete doors and windows, sun protection, heat insulation, and good ventilation. Improve storage conditions in warehouses, control storage temperature and humidity, and use chemicals to exterminate insects when necessary.
3.3.2 Day-to-day management Effective sealing of the seals and cut-off of moisture and oxygen absorption channels can effectively prevent mildew. Feed products should be protected from rain and sunlight during transportation. The marketing and storage of feed products should be emphasized to middle marketers and users.
Shorten the shelf-life of aquatic feed products and raw materials, and stocks of raw materials should have a proper amount of inventory; however, it should not be purchased in large quantities, and half-month consumption is generally appropriate. The production of products must be strictly enforced with the production-by-production system. After the products are produced, they will be released within 7 to 10 days, and the product quality guarantee period system will be strictly enforced according to season and species.
3.4 Application of Aquatic Feed Antifungal Agent
3.4.1 Single anti-mould agent At present, China's aquatic product antifungal agents such as Crerein, Leijingjing, and Mycophenolate 101, etc., are mainly composed of propionic acid and its salts. Imported feed anti-mildew products such as Propagyl Salt, Wanlubao, Kejiaba, and Huaximycin, etc., are mainly propionic acid, and the main component of the exposed salt is calcium propionate. Other anti-mildew agents include sorbic acid and potassium sorbate, sodium sorbate, calcium sorbate, benzoic acid, sodium benzoate, fumaric acid and fumarate, calcium formate, dehydroacetic acid and sodium dehydroacetate. and many more.
3.4.2 Compound anti-mold agents In addition to the use of a single type of anti-mold agent, the current trend in the use of anti-mould agents in the world is to use composite anti-mold agents, which are a variety of organic acid anti-fungal agents, according to a certain proportion Cooperate. This compound anti-mold agent can broaden the scope of antibacterial spectrum and enhance the anti-mold effect. Compound fungicides commonly used in Japan include: 1) It consists of 92% seaweed, 4% calcium iodate, and 4% calcium propionate. When used, it is added to the feed at a rate of 8%. This anti-mould agent is not only In addition to the good mold effect, the most important feature is to increase the various trace elements in seaweed, such as calcium, iron, zinc, iodine, copper, etc., so that the trace elements in feed more abundant; 2) from 1 part of sodium acetate and 2 parts of aldehyde The acid is mixed, then 1% sorbic acid is added to the mixture, stirred well and dried, and added to the feed at a proportion of 1% in the use; 3) mixed with 1 part of sodium carbonate and 2 parts of aldehyde acid, and then added to the mixture One percent of sorbic acid is well mixed and dried. When used, it is added to the feed in a 1% ratio.
It should be noted that either single or compound anti-mould agents are used. Generally do not mix with alkaline substances to enhance the anti-mildew effect.

4 New directions for research on anti-mildew measures for aquafeeds
4.1 Development of Green and Mildewproof Technology China is the earliest country to use natural anti-fungal agents in Chinese herbal medicine. It has been proved that fennel, pepper, pepper, and waterwool with volatile odor have good anti-corrosion and mildew-proof effects. Subsidiary residues do not affect the normal metabolism of aquatic animals. The application of natural materials and bio-mildew prevention has been gaining momentum and has attracted the attention of researchers.
4.2 The development of new types of mycotoxins has been harmed by mycotoxins. Zeolite has been used for adsorption. However, due to the large amount of addition, it affects the balance of nutrients in the feed and interferes with the use of amino acids and minerals. This does not really solve the problem. Esterified glucomannans are now used internationally to adsorb mycotoxins. The glucan in the inner layer of the yeast cell wall is not active, but after being transformed into a Mycosorb, it greatly increases the surface area and has an adsorption capacity, and can adsorb a variety of mycotoxins (aflatoxins, T-2 toxins), and not It will have adverse effects on other nutrients.

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