Pathogenic effect of feed pollution on fish

At present, due to the phenomenon that the content of bacteria in some feed products seriously exceeds the standard, the phenomenon of fish death occurs from time to time after fish ingest contaminated feed. According to the symptoms of fish disease can be divided into two types: acute type (fulminant) and chronic type.

1. Acute type (fulminant type): after eating contaminated feed, most fish get sick for 3 ~ 5 days, and as little as 1 ~ 2 days, the disease occurs, and the seriously ill fish have died, and the amount of dead fish is gradually increasing, but it does not affect food intake. Most fish can eat normally. The symptoms of this kind of fish are similar to those of hemorrhagic septicemia. The diseased fish showed systemic bleeding with large hemorrhagic spots on both sides of the body surface and abdomen. Chest, pectoral fin, Gill cover edge, jaw serious bleeding, showing bright red, diseased fish anus red. Anatomical examination showed that the diseased fish suffered from severe enteritis, enlarged hepatopancreas, dilated gallbladder, thick green bile and cholestatic symptoms.

Second, chronic type: after eating a certain amount of contaminated feed or a certain amount of contaminated feed raw materials, most fish show symptoms for one month or 40 days, and as little as 10 ~ 20 days, the symptoms are mild at the beginning, and then get worse gradually. At the beginning of the disease, loss of appetite, do not rush to eat, food intake is weak, and the body color is black. With the passage of time, some fish do not go to the food table to grab food, but only swim around. Individual fish eat as if they were frightened, and suddenly swim away after eating, so that the pieces of fish suddenly swim away, and the eating fish decreases gradually. in serious cases, most of the fish refuse to eat, and there is gradual death of fish. Anatomical examination showed that most of the fish showed typical symptoms of enteritis. The mucous layer of the intestinal epithelium of the diseased fish was exfoliated and transparent, with colorless or yellowish mucous or watery liquid and some bubbly gases. In addition, in production, there are subacute cases between acute type and chronic type in terms of symptoms, course of disease and loss of death. most of the contaminated feed consumed by fish is 10 ~ 20 days, and as little as 7 days, that is, symptoms occur and dead fish occur. Fish with this type of disease, except for typical enteritis, other symptoms and dead fish are not as obvious as acute type. Contaminated feed can not only cause vertebrate fish poisoning, but also cause crustacean crab disease and death. After the fish ate contaminated feed, the symptoms of light, severe, slow and acute disease, the amount of dead fish were related to the degree of feed pollution and the total content of bacteria to a certain extent. The more serious the feed pollution and the higher the content of bacteria, the more urgent the disease of fish, the more obvious the symptoms, the greater the amount of dead fish, the more serious the loss, otherwise, the opposite. In the process of production, processing, storage and transportation of toxic and harmful components of feed pollution, the process of infection, colonization, reproduction and growth by microorganisms such as bacteria and mold is called feed biological pollution. As a result of the pollution harm caused by feed microbial pollution, the toxic and harmful components produced are also different. Feed pollution can be divided into three situations: 1. The feed is polluted by a large number of saprophytic bacteria, the bacterial phase is complex, the total number of bacteria is high, and the nutritional quality of the feed decreases. Various nutrients are degraded, decomposed and hydrolyzed to produce many toxic and harmful substances, which make the feed deteriorate and have a toxic effect on fish. High-protein animal feed: most of the protein in this kind of feed can be decomposed under the action of bacteria to produce harmful base nitrogen compounds, such as amine, hydroxylamine, hydrogen, etc., emitting a choking ammonia odor. Carbohydrate feed such as flour, corn flour, cereal and so on: carbohydrate feed is hydrolyzed to hydroxyl OH, alcohol, aldehyde, CO_2 and other substances under the action of microorganisms, especially cereal feed is very easy to produce this kind of hydrolysis reaction when the weather is hot and the temperature is high, emitting rotten smell. Oil feed: such as undefatted fish meal, cake feed, peanut cake, sesame cake, etc., which can produce rancidity reaction, produce "ha flavor" smell, and produce ketones and aldehydes, which are highly toxic to fish. two。 Feed is contaminated by pathogens and becomes the carrier and disseminator of pathogen. If the feed is contaminated by land animal pathogens and salmonella, it can also lead to fish disease. 3. A large number of toxin products produced by microbial bacteria and mold pollution, such as mold-Aspergillus flavus contaminated feed, can produce aflatoxin B1 and B2, which are toxic to fish. In the artificial compound feed composed of a variety of raw materials consumed by fish, the results of the above three types of changes after feed pollution are often biological, physical, chemical and complex comprehensive processes. the toxic and harmful substances produced are also diverse, compound and interact with each other, rather than a single type. The symptoms of fish after eating contaminated feed is also a very complicated biological process. It has a certain correlation with the nutrition, physical condition and water quality of the fish.