Examination of sick fish

The fish were examined for symptoms, symptoms, pathogen identification and histopathological examination.
1 external symptoms of examination
The external symptoms of the sick fish were examined mainly by the visual identification of symptoms and pathogens. In general, the symptoms of different pathogens are different from the symptoms caused by fish. The main pathogens are divided into two major categories of microbial and parasitic. The parasite that causes the disease often show excess mucus, bleeding, punctate or massive cyst and other symptoms, especially some large parasites, such as worms, crustaceans and size larger protozoa (such as sticky robe worm cyst, etc.), with the naked eye can see that. The disease caused by pathogenic microorganisms, more performance for the fish body hyperaemia, inflammation, abscess, decay, fin erosion, vertical scales and other symptoms.
According to the general order of the site is from the surface to the gills,
(1) surface from aquaculture fish out just dead or dying of disease fish and placed in white porcelain or fish plate, along the head, drive cadres to tail, namely according to the sequence of mouth, eyes, operculum, scales, fins and friends careful observation,
Some of the major pathogens, such as water mold, nematodes, anchor head), louse, glochidium and sticky Cryptosporidium cysts etc., easily detectable. But some small pathogens, the naked eye can not see, then should be judged according to the symptoms. Such as car rotifers, wave fish Bodo, Chilodonella, Ichthyophthirius, three generations of insects, such as caused by the symptoms, the general will lead to the excessive secretion of mucus of fish body surface, sometimes mixed with sludge, or is the head, mouth and node end rot, but Jing strip base department generally does not appear congestion phenomenon. The complex mouth of the fluke disease, the performance of the eyeball, the ax, there is a cataract. Grass carp hemorrhage, bleeding in the oral, head, eyes to sleep, fin base, jaw, operculum and abdominal occasional light red blood spots. Bacterial red skin disease, performance for shedding scales, skin congestion; furunculosis is in lesion inflammation and abscess; leukoderma is lesion inflammation, reduce mucus, rough to the touch; print disease is in massive erosion of decay for the disease. However, some symptoms, including symptoms of skin, gill disease, different disease symptoms are basically the same situation, such as red skin disease, gill rot disease, enteritis and other parts of the bacterial disease are symptoms of fin base congestion and moth fin, so fish disease diagnosis, unlike the diagnosis of human disease that interrogation, only through detailed investigation and comprehensive symptoms are analyzed, in order to make the accurate diagnosis and correct.
(2) the examination of the gill, with emphasis on the gill filaments. First observe the gill cover is opened inflation, then used a pair of scissors to the operculum to cut, the observation of the gill lamellae color is normal, mucus, gill filament end whether there enlargement decay. Bacterial Gill Rot Disease gill decay in the end, many mucous; Branchiomycosis gill lamellae of color than normal fish gill lamellae of the color white, tinged with blood red dots; if wave fish Bodo, cryptobia, Trichodina, Chilodonella, Dactylogyrus and insects, such as parasitic, gill plate more mucus; if Chinese Sao, narrowly abdominal), single insects and some Dactylogyrus and myxospore insect cell capsule and parasitic, gill enlargement, opercular swelling and other symptoms.
Internal symptom check
Check fish tissue disease mainly to gut check, the fish on the side of the abdominal wall cut off, the first observation of whether there is ascites and visible to the naked eye fish strange, nematodes, ligula intestinalis and other parasites; carefully observed the internal appearance is normal; then with a pair of scissors from by the throat of the foregut and by the anus intestine cut, remove the internal organs, placed in a white porcelain, one by one from liver, gall bladder, bladder and other organs. Finally, the intestinal once the gut and hindgut cut open, divided into before, during and after the three sections, gently put food and feces in the intestinal tract removed, carefully examined. Intestinal parasitic trematodes, cestodes, nematodes can be easily seen; bacterial enteritis will exhibit intestinal hyperemia and inflammation; hemorrhage of grass carp is intestinal or local is bright red bleeding, enteral without food, but the intestinal wall is still relatively strong, erosion; coccidiosis and sticky Cryptosporidium disease is in the intestinal wall with sheets or dilute the white dots scattered. Other internal organs, if not found in the appearance of symptoms, the general can no longer check.
Do check the detailed record, for fish disease diagnosis provide correct basis, and fish disease diagnosis and improve farming techniques accumulated data and experience.
3 pathogen identification
Pathogen identification is generally used in optical microscopy, and the anatomy of the disease fish to do a deeper pathogenic, pathological examination. With the exception of some of the more obvious and fish disease condition and relatively simple, by visual inspection can accurate diagnosis, the general must be microscopy can be diagnosed.
The examination of the lesions was carried out in the selected area, and the location and sequence of the examination were the same as the target.
Check method is from the lesion site from small amounts of tissue or mucous placed slide on, such as skin and gill tissues or mucus, plus a small amount of ordinary water, internal organs should add a small amount of normal saline (0.85% saline water), and then covered with coverslips, and slightly flattened, placed under the optical microscope observation. In order to accurately, at least 3 different points of each lesion were examined.
When in water bodies of the same breed, there are more than two kinds of fish, you need to to various pathogens and intensity of infection and the fish in the degree of damage were compared and analyzed, identified the major and minor pathogens, in order to facilitate the development of therapeutic measures.

Diagnosis of fish diseases

Correct diagnosis of diseases of fish and aquatic animals is an important part of preventing and curing diseases. Only through field investigation, detailed examination of diseased fish, in order to achieve accurate diagnosis, suit the remedy to the case, in order to achieve the purpose of effective treatment, in order to provide the basis for taking further measures of preventing disease and breeding.
Field investigation
The purpose of the survey is to understand the pathological phenomenon, feeding management and water quality changes in the fish, and provide the first hand data for the comprehensive analysis and accurate diagnosis of the disease.
Pathological phenomena and medical history of fish culture
The genesis of fishes and aquatic economic animal diseases, acute and chronic, acute disease, body color and the constitution of the fish body with normal little difference, but careful observation, lesions vary slightly. In the short term, there will be a peak of death. Chronic diseases, the body color of the fish body black hair, emaciated body, travel alone, slow activity, mortality increased slowly, in a relatively long time peak mortality occurred, some do not appear the death peak, just a long time continuous fish. When the fish in the water set door prefectural uneasy, a shoe to jump, while dramatically mad swim should pay attention to two, either the body surface of fish parasites invasion, or that is in the water containing toxic substances, such as pesticides or toxic industrial wastewater. The former showed a slow increase in the number of deaths, but the death rate was not high, then a large number of deaths, and including wild fish, including the death of a variety of fish.
In aquiculture water the same. Every year the emergence of a fish, such as sticky Cryptosporidium disease, bacterial septicemia and, should history investigation, for fish disease diagnosis to provide information, in order to take effective measures.
Feeding and management situation investigation
Fish and aquatic economic animals, often associated with poor feeding and management. Application without the rotten manure or dosage is too large, commercial feeds are of poor quality or fed too much, will cause the deterioration of water quality, oxygen in the water, to the growth of pathogens and predators, reproduction provide a favorable environment. On the contrary, the water quality is thin, lack of food, and can cause anemia, a disease. Trawl and other improper operation, it is very easy to cause the white fish injury, disease and saprolegniasis. Therefore, the specific circumstances of the various aspects of fertilization, feeding, and dragnet operation and stocking varieties and specifications, density and onset of the calendar year should detailed investigation.
Investigation on water quality of aquaculture water
Water pH value and dissolved oxygen changes but also caused one of the reasons of fish diseases, especially suspected by the water quality changes cause the death of fish, but also to the laboratory for chemical composition of water analysis. In the greenhouse environment, we should take into consideration the need to improve the control system such as light, circulating water, and so on.

Fish body to disease susceptibility and resistance to disease

After the pathogen enters the water body, the lack of fish and aquatic animals, the disease still does not occur, so the susceptible and resistant to the fish and aquatic animals are essential conditions for the occurrence of diseases. Such as the occurrence of hemorrhagic disease of grass carp silver carp, catfish, not a body without injury is not unboiled water mildew and susceptibility to disease in animal breeding is with the non-specific immunity and specific immunity of the strength of the two changes.
According to fish immune response to antigen targeted, divided into non specific immunity and specific immunity,
Non specific immunity, at least including physiological factors, physical defense structure of the two part.
Non – specific immunity from physiological factors, with age, body temperature, nutrition and breathing and so on. Such as cryptobiosis and Trichodina disease is fry, fingerling stage common parasite epidemics, and with the growth of the age of the fish body, even with the presence of pathogens. It is not easy to cause disease occurrence; Jiujiang Bothriocephalus acheilognathi usually not parasitic in 1 above the age of grass carp intestine, in low temperature cold northern area or in fall and winter, most microbial carbon diseases, such as hemorrhagic disease of grass carp, Bacterial Gill Rot Disease of sex, enteritis will not occur. Under the condition of hypoxia, fish are prone to disease.
The main factors that affect the immune function of non specific immunity in fish are the scale, skin and other surface barrier, and the second line of defense. Scales, skin and mucus is an important barrier for parasite invasion of the fish body resistance. Therefore, the protection of fish body surface is not damaged and without predators attack injured, pathogen could not invade, leaf spot, tail handle disease, disease and water mildew of print would not have happened. The concentration of chemical substances in the breeding water is too high, which can cause the fish to secrete a large amount of mucus, and once the excess secretion of mucus, it can not protect the role of the fish, and can not resist the invasion of pathogenic bacteria. After entering the body of the pathogen, the pathogen of the pathogen is often swallowed up by the phagocytic cells, and attracts the white blood cell to the injured site to swallow the pathogenic microorganism, which shows the inflammatory reaction. When the phagocytic cells and the phagocytic ability of white blood cells can not stop the rapid growth and reproduction of pathogenic microorganisms, the local lesions will be expanded, more than the fish body’s tolerance and lead to fish death. Therefore, health cultivation is an important measure to prevent the disease.
Specific immunity is the body of the body in the process of life to accept the foreign body to stimulate the immune system, also known as acquired immunity. According to the different ways of the different, can be divided into automatic and passive immunization. In addition to a very small number of viral and bacterial diseases can be obtained after a specific immunity, can be lifelong immunity, the vast majority of the disease’s specific immunity has a certain time limit. Such as patient Lernaea disease of silver carp and bighead carp can produce specific immunity, but not lifelong immunity of grass carp hemorrhage immune killing injections of vaccine, immunity can keep 14 months and thereafter gradually decreased. Therefore, according to the master of fish disease causes, control and improve aquaculture water environmental conditions, enhancement of fishes and aquatic economic animals body resistance is the key to the prevention and treatment of diseases of the livestock.

Analysis of fish disease pathogen

Disease of freshwater fishes in China has more than 100, and the shrimp disease, disease frog, turtle disease and aquaculture fish disease, kinds is more, the pathogens are viruses, bacteria, fungi, algae, protozoa and trematodes, nematodes, Acanthocephala, tapeworm, leeches, the Glochidia larvae, crustaceans and other. Some of these pathogens often make the fish sick, causing many diseases, common diseases,
In aquaculture water, if there is no pathogen, or at least pathogens control in the degree of damage to the extent of the following, fish and aquatic animal diseases will not occur, the pathogen is parasitic organisms, they can not survive or thrive in the environment of the outside world, and must be in the main body of the breeding. Source of infection of pathogenic diseases come from the fish, especially parasitic pathogens and not a moment in the pathogenesis of carry pathogens, pathogenic spread faster and more subtle. Some parasitic diseases infectious bird. Animals and humans, such as export trematodes, ligulosis source of infection is of European birds, herons and other birds, fish Clonorchis vampire disease to infect a source are cats, dogs and other mammals, the human body is also infected with the disease, the original Hugh reports, some fish parasites, the developmental stage of the larval stage is spent in birds, animals or humans, so bird, animal or human has become some fish parasitic disease to infect a source,
Fish pathogens discharged into the water, with water irrigation and drainage into other aquaculture water, the waters of the original pathogen becomes foci.
Contagious pathogens and the strength of the pathogen in the host settle, reproduction and discharged from the host number has a close relationship, is conducive to the parasite growth and reproduction of the environment, the infectious force will be very strong; on the contrary, the drugs to kill and ecological methods inhibition of pathogen activity make it infectious reduction or elimination of pathogens, is not conducive to the parasite growth and reproduction, fish has a chance of less.
The virulence of the pathogen is the ability of the pathogen to cause disease, and it is determined by the number of pathogens. The number of species in the living environment, the virulence of pathogenic bacteria and the strong and weak points. Larger number of pathogens in fish, fish disease symptoms of more serious, such as more than 10 Chinese) parasitic in 2nd instar gill of grass carp, grass carp and no significant response to the disease; and when hundreds of parasites in strontium grass carp, it will cause the gill filaments to inflammation of the end, pale and swollen, bending deformation, anemia, sick fish irritability, but also in wound bacterial infection, concurrent disease caused by bacteria, serious will cause mass mortality of grass carp.
The pathogen is the result of a prerequisite for the occurrence of fish diseases. Cut off pathogens in aquaculture water route of infection, or according to the characteristics of pathogen infectivity and pathogenicity, targeted for ecological control, drug prevention and immune prevention, reduce fish, its control below the extent of damage, in order to reduce economic losses.

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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