The causes of fish diseases

Fish and aquatic animals, like all living things, need to have a living environment that is suitable for them. Fish live in the water environment, you have to have a good water environment and continuously enhance the ability to adapt to the environment, with high yield for the purpose, many of the environmental conditions of the water body is under the control of artificial. If the breeding environment has changed, is not conducive to the survival of the living, living, or the body of the body should not be adapted to the living environment, fish and aquatic animals will lose the ability to resist the invasion of pathogens, it will cause the disease.
The occurrence of fish diseases or not, is mainly determined by environmental factors, disease resistance and susceptibility to pathogens and fish etc..
Environmental factor
The environmental factors of fish diseases including natural conditions, human factors and biological factors.
1 natural conditions
(1) water aquaculture, fish are poikilotherm, changes in water temperature with the temperature elevating life change. The sharp fluctuation of water temperature, fish body is not easy to adapt to the pathological changes and even death. Such as fish pond, water temperature and water temperature of raw water of life is not more than 2 DEG C, species of not more than 4 DEG C. The temperature difference is too large, it will lead to a large number of dead fish fry, put the fish, that is, the main reason for low survival. All kinds of pathogens in the appropriate temperature of water will also be a large number of breeding, leading to fish sick.
(2) the water quality of aquaculture water, fish can not do without water, better water quality environment is more conducive to the growth of fish. The changes of water quality according to the determination of pH value, dissolved oxygen, organic oxygen consumption, fatness and transparency to determine, although fish for aquaculture water pH value have great adaptation range, but at pH value 7 to 8.5 appropriate, if below pH 5 and pH value is higher than the 9.5, the lighter the fish growth bad, the person that weigh fish deaths caused by. As addicted to dinoflagellates “caused by acid egg powder is acidic water, disease” results. Have a direct impact on the level of dissolved oxygen content in the aquaculture of fish growth and survival, per liter of water dissolved oxygen content of less than 1 mg, the fish will “floating head”, if you do not take timely measures of Zo oxygen, will make the fish suffocate to death. When the weather is hot and the air pressure is low, the phenomenon of hypoxia is the most common. There are many harmful substances in the waste water of the environment, which can cause the fish to be deformed, or cause the bubble disease,
(3) in the bottom of the water body, the bottom sediment is the soil and the silt layer which is in contact with the water. In particular, the sludge contains a large amount of nutrients, such as organic matter and nitrogen, phosphorus, potassium, etc., through the decomposition of fine seedlings and ion exchange, and constantly dissolved and released to the water, to provide the food for the growth of nutrients. The mud has fertilizer, fertilizer preservation and regulate water quality, keep the amount of silt layer is necessary. However silt accumulation, organic oxygen consumption is too large, in the summer and autumn easily lead to fish in the hypoxic, but also make the water turns sour, thus inhibit fish growth, even endanger the fish life. Nutrient substance in the sludge is a good medium for pathogenic bacteria, and some inorganic substances can enhance the virulence of the disease. The more silt accumulation, the more likely the disease occurs. Practice has proved, in aquaculture sediment dredging, drying pond disinfection, fish incidence can be decreased. Nowadays, there are many short acting sex, in the long term is not clear silt, bring endless trouble to the sustainable development of aquaculture, occurrence of fish diseases will be very hard to detect, serious will likely crops. You often freshwater fish bacterial septicemia and the long term is not clear there is a direct relationship between silt.
Human factor
(1) the stocking density and improper polyculture imbalance
Polyculture of varieties and proportion and stocking density and fish disease have great relationship, such as per unit area in the stocking density is too large or, fish from the lower proportion of improper collocation, resulting in lack of Nai, malnutrition, weaken the resistance of fish, but also a waste of available water.
(2) aquaculture mismanagement should strictly adhere to the “four fire”, “four” technical specification for aquaculture. Artificial feeding should be according to the amount of the fish body daily need, not Zhang full, feeding are not, more can not vote feed do not clean or metamorphic bait, corruption of plants, dead stinky the snail, with parasite eggs and pathogenic vaccine bait. Otherwise, the growth rate will reduce the fish, the fish body resistance weakened, leading to disease epidemic.
(3 mechanical damage, net fishing and transportation of fingerlings can easily scratch the fish body, making it susceptible to fine seedlings, water mold etc. the causative pathogens. Such as the water is the parasitic in the injured area of the.
3, biological factors
To make fish pathogenic organisms, known as fish pathogens, by virus, small seedlings, seedlings and algae invasion caused the fish, commonly known for infectious diseases of fish; fish diseases caused by protozoa and trematodes, cestodes and nematodes, crustaceans and other parasites, known as parasitic fish disease. In addition, there are many cultured fish predators, such as a mouse, birds, snakes, frogs, ferocious fish, aquatic insects, Hydra, qingni moss, Hydrodictyon reticulatum.
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