Chapter VIII: Prevention and Control of Fish Diseases
Harm of Fish Diseases on Aquaculture
Aquatic animal disease prevention and control is an integral part of aquaculture and its direct economic benefits are embodied in the aquaculture industry itself. Neglect of prevention and treatment of disease or passive attitude towards disease prevention and control will result in serious decline of aquaculture. Based on the current status of breeding and estimation of the size and occurrence of disease, disease may cause industrial loss of up to 30% -50%. Various researches of disease control and prevention can reduce losses due to diseases by more than a half.
Effective disease prevention is an important measure to improve the aquaculture production of aquatic animals and increase economic efficiency.
Aquatic animals live in water. It is difficult to detect when they fall ill so that timely and correct diagnosis is more difficult;
Drug administration difficulties: The medication can only be eaten actively by aquatic animals; and in vitro treatment is only suitable for small waters.
Implementation of the "comprehensive prevention and aggressive treatment" approach and take the positive way of "prevention of disease and early treatment."
Section I Reasons for Fish Diseases
I. Relationship among pathogen, fish and pond environment
Fishes are aquatic animals living in the water throughout its lifetime. Fishes perform feeding, respiration, excretion, growth and all other life activities in water. Thus, water environment has greater impact on fish survival and growth than any other land animals. The number of pathogens in water is larger than that in the terrestrial environment. Various physical and chemical factors (such as dissolved oxygen, temperature; pH value, inorganic three nitrogen, etc.) in water directly affect fish survival, growth and diseases.
Physically healthy fish is more adapted to the environment and strong in resilience to diseases. However, in ponds, as stocking density is increased (several times or even several times larger than the natural waters), the amount of artificial feeding and fish excretion on water pollution increase, making the environment easy deterioration. Meanwhile, it is more likely to suffer disease. In case of environmental degradation, if pathogens cause more harm than fish’s inherent immunity, it leads to the occurrence of fish diseases.
II. Environmental Factors for Occurrence of Fish Diseases
(I) Physical and chemical factors
Physical factors: temperature and transparency. Generally, with increase of temperature, reduction of transparency and faster propagation of pathogens, the occurrence of fish diseases rises except individual types of pathogens, such as water molds, small point-like very gross bacteria (pathogen vaccine vertical scales) and so on.
Chemical factors: water chemistry indicators are the main indicator of water quality and are also the main factors leading to the occurrence of fish diseases. They mainly refer to dissolved oxygen, pH, and ammonia nitrogen content in pond. When the dissolved oxygen is adequate (more than 4 mg per liter), pH value is suitable (7.5 ~ 8.5), and ammonia nitrogen is low (0.2 mg per liter or less), the occurrence of fish diseases is low, whereas the occurrence of fish diseases is high. In case of hypoxic, fish are easy to infect fin rot, and in case of pH value of below 7, it is very easily to be infected with a variety of bacterial diseases, and in case of high ammonia nitrogen, it is easy to suffer fulminant hemorrhage.
(II) Biological factors
Plankton organisms and pathogens are related with fish disease. Too much phytoplankton or bad types of phytoplankton (such as cyanobacteria and algae) are considered as aging of water quality. This kind of water is easy to cause high occurrence of fish diseases. In case of higher level of biological pathogens, fish are easier to suffer increase. Meanwhile, the number of host organism also directly affects spread speed of the corresponding diseases (such spread of taeniasis by copepods).
(III) Human factors
In intensive ponds, man-made factors greatly accelerate the occurrence of fish diseases. For example, too large stocking density, a large number of artificial diets, mechanical operation and etc. may substantially increase occurrence of fish diseases. Thus, the intensive pond suffers high occurrence of fish diseases. Thus, disease prevention and treatment becomes more important.
(IV) Pond conditions
It mainly refers to the size and pond sediment. Generally, small ponds suffer great changes in temperature and water quality, and the occurrence of fish disease is higher than large ponds. The ponds with turfy sediment generally have low pH values so that it is conducive to the propagation of pathogens so as to result in higher occurrence of fish diseases. Thick-sediment ponds have high levels of pathogens, toxic and hazardous chemical indicators so that they are generally more likely to suffer fish disease.
III. Physical Factors for Occurrence of Fish Diseases
Fish body status is intrinsic physical factor for fish disease and is the root cause of fish disease. It mainly refers to species and physical status. Hybrid species are stronger in resistance to diseases than the pure species, and the local species are stronger in it than the introduced species. Physically good fish have good function of various organs and are strong in immunity and resistance to disease so that the occurrence of fish diseases is low. Fish’s physical status is also closely related with the feed nutrition. When fish are fed with adequate feed with balanced nutrition, they suffer less disease, or fish are weak in ability to withstand a variety of pathogens and are most susceptible to infection of disease. At the same time imbalanced nutrition will also a directly result in a variety of nutritional diseases, such as thin spinal diseases, collapsed gill disease, fatty liver and so on.
Section II Examination and Diagnosis of Fish Diseases
I. Field investigation
(I) To understand a variety of abnormalities of fish
When fishes are sick, various symptoms emerge on fish body surface. Meanwhile, water will demonstrate a variety of abnormalities, such as black body and traveling alone. In normal climate and all normal circumstances, the fish’s food intake suffers sudden and sharp fall. Fish diseases are divided into acute type and chronic type. In case of acute-type diseases, sick fish are not very different with the normal fish in body color, appearance and physical status, only a slight change in the lesion. In the event of death, the death rate increases dramatically. In case of chronic type diseases, fish are often physical weight loss, activity is slow, the body color is black, and they travel alone, with the mortality rate generally slowly rising. Invasion by parasites, they often appear restless.
In case of invasion of fish louse, fish suffer little change in color, but they will jump up and down crazily. When Myxobolus drjagini attacks silver carp, the tail of fish will turn up out of the water, swim in the water in circle crazily. In case of fish poisoning due to pesticides or industrial discharges, fish will show jumping and collision phenomena. Generally, in a relatively short period of time, they will suffer paralysis or even death. Death caused by parasites is generally slowly increased. Except death caused by Dactylogyrus and Gyrodactylus invasion, generally the death rate will not be too high. However, in case of fish poisoning, in a very short period of time, there will be a large number of fish killed, regardless of species. Therefore, timely observation of the activities of fish in site is of vital importance for fish disease diagnosis and timely treatment.
(II) To understand water quality and environmental conditions
Water temperature and fish disease prevalence are closely related. The growth of various pathogens has its optimum growth temperature range. For many kinds of pathogenic bacteria and viruses, at average temperature of around 25℃, the toxicity is significantly increased. When the water temperature drops below 20℃, then virulence is reduced, and the disease condition is reduced or stopped. Chilodonella’s suitable water temperature is 12 ~ 18C. Ichthyophthirius growth and reproduction water temperature is 15 ~ 25C. When the water temperature is lower than 10℃ or above 26 ℃, then growing will stop. Observe the color of water to know about the water quality conditions. In case of much humus in water, water is brown; when water contains much calcium, it shows sky-blue color; in case of much Microcystis, water is aeruginous. Urban sewage is generally black. When contaminated by contamination source, there are different colors due to sewage type and different nature, such as red, black, gray and etc.. Transparency will also be greatly reduced.
Dissolved oxygen, hydrogen sulfide, pH, chlorides and sulfides are related with the fish diseases. Some ponds are not cleared for several years, and some cages are placed in the same place for many years so that a large number of bait fish feces will deposit. When dissolved oxygen is reduced, fish will suffer anoxia or even death. Water with many organic matters and smelly water are suitable for reproduction of gills so as to cause branchiomycosis. Acidic water often causes eosinophilic eggs dinoflagellate disease. High content of chloride and hardness will encourage reproduction of small Primnesium saltans, causing fish poisoning and even death.
We should understand the surrounding environment, to make sure the existence of sources of pollution or epidemic spread source, pond surrounding sanitation, number and activities of livestock, poultry, birds, snail mussels and their predators. Especially, for some sharp dead phenomenon, we need to understand the situation around the factories discharge of sewage. In terms of industrial wastewater and pesticides, we should pay special attention to phenol, heavy metal salts, cyanides, acids, alkalis, organic pesticides, organic chlorine and organic arsenic and other harmful matters. In case of diagnosis of poisoning, we should quickly understand the type of pesticide or main lethal chemical composition in sewage so as to take emergent measures.
II. Examination of Fish Disease
(I) Visual inspection of fish
Visual inspection of fish is referred to as visual inspection. In actual production, visual inspection is one of the main methods to check fish diseases. Visual inspection can observe the symptoms of the body after pathogen invasion. For some diseases with obvious symptoms, the experienced technical staff can make preliminary diagnosis by visual inspection. In addition, some large pathogens such as large parasites can also be observed by eyes.
General viral and bacterial fish diseases often show congestion, inflammation, decay, abscess, bore fins, vertical scales and so on. Fish pathogenic viruses and bacteria can be determined by sophisticated equipment and professional technical personnel. At the same time, cultivation and identification of pathogenic bacteria also requires a longer time. Thus, in actual production, after the parasite is usually excluded, according to the symptoms of diseases, type of fish diseases can be roughly defined.
Parasites fish diseases often show excessive mucus, blood, feather cysts dot or block, etc.. According to parasite location and different symptoms, some can be accurately diagnosed by naked eyes. As for inspection of fish, it mainly refers to inspection of the body surface, gills and internal organs. Check order and method are as follows:
Surface: the sick fish will be placed in white enamel plate and inspected in order from the mouth, head, gills and body surface to fins carefully. Parasitic nematodes, lernaea, fish louse, glochidium, water mold and other large pathogens on the surface can easily be observed and determined. However, a lot of small pathogens that can not be seen by the naked eyes are mainly identified based on the presented symptoms. The symptoms caused by ichthyobodo, trichodina, chilodonella and gyrodactylus usually show a lot of mucus, and sometimes with a little sludge or the mouth, head and fins end rotted but the fin base generally does not suffer congestion.
Furunculosis is manifested in lesion inflammation and abscess. Leukoderma shows white lesion location, less mucus and rough sense of touch. Diplostomum shows eye fluke and late cataract. However, some symptoms such as congestion and moth fin are one of symptoms for red-skin disease, enteritis, gill rot and other bacterial diseases. If a lot of trichodina, chilodonella, ichthyophthirius, dactylogyriasis and other parasites on the body surface or gills of fish, it will also stimulate fish to secret more mucus. So, in addition to the symptoms of sick fish, we should also consider the living habits and conditions of pathogen, main host and so on.
Gills: Check the gills, with emphasis on the gill filaments. Check whether the gill cover is open, then use scissors to carefully cut the gill cover to observe whether gill filaments are swelling or rotted, whether gill color is normal and whether mucus is increased.
In case of bacterial gill rot disease, the end of gill filament will rot and for seriously sick fish, tunica intima in middle of gill cover often rots into irregular circular "small window". In case of gill mold, the gill color will be white, with some reddish dots. In case of diseases caused by trichodina, chilodonella, C.branchialis, Dactylogyrus and Gyrodactylus and other parasites, gill will have more mucus. In case of Sinergasilus, Diplozoidae, Lamproglena, Myxosporidia and other parasites, it usually shows swollen gills and open gill cover and other symptoms. In case of a lot of Ichthyophthirius and Cryptosporidium, the naked eyes can see a lot of white spots, so it is often known as the "white-spot disease."
Visceral organs: when we check the visceral organs, we should first cut one abdominal wall, without damaging visceral organs. First, we should see if there is ascites or visible large parasites. Then, we should observe the appearance of internal organs, such as the color of the liver, whether gallbladder is swelling and whether intestines are normal. Then, cut foregut near the throat and hindgut near the anus, remove the internal organs, put the liver, intestines, bladder and gallbladder separately, and then divide intestines into the foregut, midgut and hindgut, gently remove food and feces in the intestines, and then observe. Tapeworms, flukes, nematodes and other relatively large parasites are easy to see. In case of colitis, intestinal inflammation and congestion will be found; in case of coccidiosis and Myxosporidiosis, there will be generally large nodule in the gut and milky white slurry in the nodule or white points scattered on the intestine wall.
(II) Microscopy of Fish Diseases
Checking fish disease by microscope, dissection microscope and magnifier is referred to as the microscopy. Microscopy is the further inspection in case that fish disease situation is more complex and that visual inspection alone can not make the correct diagnosis. In general, fish diseases are often complex, and many pathogens are small. In addition to some obvious and simple situation that can be determined by visual inspection, in general, there is a need for microscopy.
Matters needing attention for inspection:
We should use live sick fish or just-dead sick fish for check. As the fish die, the parasites die soon, and pathogens in fish are very small and often soon decompose or changes in shape after death of. Thus, it is difficult to determine the pathogen after a long time.
We should keep the sick fish moist. When fish dry, the parasite on the surface of fish will also dry, and even the symptoms of sick fish will become not obvious or illegible. Therefore, sick fish should be kept in original feeding-water bucket or bowl.
Slide method: it is suitable for low magnification or high-powered microscope. The method is as follows: removing a small piece of tumor tissue or a small drop of inclusion on a clean slide, dropping a small drop of fresh water or salt water, covering it with slide, gently flattening it, first observing by low magnification microscope, and then observing for confusion or suspicious situation by high-powered microscope.
slide compression method: it mainly includes steps as follows: taking two about 3 to 4 mm thick slides with the size of about 6 x12 cm, first placing part of an organ or tissue and mucus on one slide, dropping proper amount of water or salt water (Note: ordinary water for body surface or mucus, and 0.56% salt water for the organs or tissues), pressing it into transparent thin layer with the other slide, and then placing it under dissection microscope or high-powered microscope for observation.
We should focus on examination of tissues and organs. All fish tissues and organs and blood may have parasitic pathogens. In the production practice, in particular, we should focus on examination of mucus, fins, gills, stomach and liver.
Mucus: in the fish body surface mucus, in addition to large visible parasites and disease symptoms, there are many invisible pathogens, such as C.agitata, ichthyobodo, trichodina , Myxosporidia and Ichthyophthirius cysts are difficult to distinguish visually. In inspection, first we should scrap fish mucus, and then place mucus under the microscope or dissection microscope for observation.
Gills: Check the gills, including steps as follows: first clipping a small piece of gill tissue with scissors, placing it on slide, dropping proper amount of water, covering the slide and placing it under the microscope; then scraping gill mucus or suspicious material and checking in the same method as above. Gills of fish are particularly vulnerable to pathogen invasion, and bacteria or parasites, gill mold, gill Cryptobia, Myxosporidia, microsporidia, dermocystidiosis, Trichodina, chilodonella, ichthyophthirius, dactylogyriasis, Hemiophrys sp., Ambiphrya, Trichophrya, Dactylogyrus, Gyrodactylus, Diplozoidae, mollusk larvae and Ergasilus etc. are often parasitic on the gills. In order to check the accurately, gills on each side should be at least checked twice or more. At the time of taking gill tissue, it is better to clip a small piece from the location of the first gill of each side, and mostly parasites are on these two positions.
Stomach: first, removing all the fatty tissue on outside wall of intestinal tract, or in inspection, the fat will enter into the gut so as not easy to observe. After removal of fat, generally visual inspection is done first to observe whether the intestinal appearance is normal. If the intestinal wall has many white spots, they are usually Myxosporidia or microsporidia cysts. After visual inspection, the gut is generally divided into foregut, midgut and hindgut respectively to be checked. Gastrointestinal tract is the most susceptible to bacteria and parasites attack. In addition to bacteria that may cause enteritis, we may also find many other parasites such as Giardia, amoeba, Myxosporidia, microsporidia, coccidia and other protozoas and Digenea trematodes, nematodes, thornheaded worms, tapeworms, etc.. Sometimes the number is still quite large. Digenea trematodes, tapeworms, nematodes and thornheaded worms usually are parasitic in foregut (stomach) or midgut; and hexamitiade, amoeba and Balantidium are usually 3 to 6 cm away from the anus of hindgut.
In addition to large parasites and parasites in the intestinal fluid, we should also pay attention to whether there are white points or nodules in internal intestinal wall and whether there is ulceration or red-hot phenomenon. If there are white spots, by crushing the cyst, we can often see a lot of Myxosporida and sometimes microsporidia. In case that Mylopharyngodon ntestinal tract suffers ulcer or white nodules, there are often a large number of coccidia parasites. In case of the red-hot phenomenon, it is generally bacterial enteritis.
Liver: first, observing with the naked eyes whether the color of the liver suffers significant change from the normal fish and whether there is ulceration, lesions, white spots and tumors. On the liver surface, sometimes we can find Paragonimus cysts or parasites and even Myxosporida, Microsporidia or Coccidia cyst white points. After observation of the appearance, taking a little tissue from the liver on the slide, covering it with cover-glass, gently flattening it, first observing it by low-powered microscope and then by high-powered microscope. Usually, in the liver of diseased fish, Myxosporida and Microsporidia cysts can be found and sometimes even Ichthyophthirius cysts.
(III) Diagnosis of Fish Diseases
Comprehensive analysis based on field investigation, visual inspection and microscopic examination can often make the final accurate diagnosis. In identifying the reasons for fish diseases, in addition to obvious symptoms, we should also pay attention to the issue whether it is caused by a single cause or by a variety of causes, and in case of simple infection, the cause is clear; and in case of mixed infection, we should determine the main cause according to type, quantity, location and of the pathogens. Only when we find out the main causes and develop effective prevention measures, treatment of fish diseases will receive immediate results.
Section III Methods for Prevention and Control of Fish Diseases
I. Strengthening water quality management of intensive pond
Water quality directly affects fish’s health and growth and feed utilization rate, so we should fully understand the characteristics of pond water environment and strengthen scientific management as well as do well in water quality regulation in terms of oxygen increase and ammonia reduction. The main measures are as follows:
Removing excess sludge at bottom of pond,
Regularly splashing quicklime (when ph value is low).
Starting aerator to reduce the underlying oxygen shortage at sunny noon in hot seasons so as to improve dissolved oxygen in water.
When the water is too fatty, killing some algae by copper sulfate and other appropriate drugs, and filling fresh water.
In high-temperature seasons, regularly applying substrate ameliorant into the high-yield ponds so as to improve water quality.
Improving water quality by photosynthesis.
II. Improving disease resistance of fish
First, according to the conditions of pond and technical level, developing a reasonable stocking density; second, depending on the weather, water quality and fish growth and activity, performing quantitative feeding at a fixed time to ensure that the fish eat well; third, choosing scientific formula and nutritionally balanced high-quality composition feed grains to avoid the occurrence of nutritional diseases of fish; Fourth, strengthening the daily management and careful operation and regular pond inspection, and in case of identifying problems, promptly resolving them and keeping pond diary; and fifth, choosing good feed with strong disease resistance capability.
III. Controlling and killing of pathogens
Fish seed quarantine: all purchased fish seeds should be quarantined.
Cleaning the pond: fish ponds should be cleaned and disinfected thoroughly.
Fish disinfection: before fish seeds are placed into the pond, they should be soaked with disinfection liquid, which can effectively kill the gill parasites and bacteria on the fish surface and gills.
Manure disinfection: organic fertilizer should not be applied before disinfection. Quicklime, bleaching powder and other drugs can be used for disinfection.
Regular prevention in growth peak seasons: ① hanging the bag or regular spilling of bactericidal drugs in peak seasons can be effective in preventing bacterial fish diseases. In case of this method, we should pay attention to the following questions: First, the drug concentration around the food site should achieve effective therapeutic concentration, without affecting the fish’s feeding. Second, the drug concentration around the food site should be kept for more than 1 hour. Third, we must continuously hang the bag or pour medicine for 3 to 5 days; ② in growth peak seasons, regular feeding of sterilization bait can be effective in the prevention of bacterial fish diseases. Bait calculation should consider the total weight of the fish, and the dosage can be reduced by 10% to 20% than usual amount for continuous 3 days.
Section IV Method and Dosage of Medication
I. Common medication method
Different treatment methods should be chosen according to the condition of fish diseases, fish species, feeding mode and spraying purposes (treatment or prevention of fish diseases). The main medication methods include the following six:
(I) All-pond spraying method
It is the most common method for prevention and control of fish diseases for pond culture. It takes the whole pond water as the object. Under the premise of calculating the correct amount of water, choose the appropriate pesticide concentration to calculate the dosage, and then dilute weighed drugs with water to evenly sprinkle throughout the pond for treatment of fish diseases. Disinfection is comprehensive and thorough, but disadvantage is high cost. Therefore, it is generally used for high-yield intensive ponds. Low-yield ponds generally use cheaper drugs except in the event of serious fish diseases.
(II) Bag-hanging method
4 to 6 medicine bags are hung in 2 to 5 meters of semi-circular area before feeding stage, the drugs in the bags are dissolved within 1 day, without affecting the fish’s feeding. Bags can be made by coarse cloth or we can directly hang the small plastic bag of drugs by making some small holes. This method is suitable for domestication feeding ponds for prevention and control of fish diseases, but it should not be used later when fish are bad in feeding. The advantage is low drug cost, easy operation and low pollution to water.
(III) Immersion method
Namely, preparing high concentration of liquid in a container (usually large plastic pot or enamel tub), then placing fish into the container for a certain time and then taking them out so as to kill pathogens on the surface and gills. The immersion time depends on the fish species, drug type, concentration and temperature. This method has the advantage of strong function, high efficacy and saving dosage. The disadvantage is that it cannot be done at any time, and only can be used in case of separating ponds and transfer of ponds.
(IV) Oral method
It is one of the methods commonly used for domesticated fish culture. Drugs are added at a certain percentage to powder particles as bait for the treatment of visceral disease, hemorrhage, vertical scale disease and so on. It is advanced in thorough treatment, less drug waste and less cost. The disadvantage is that it has no effect on the fish with serious disease and bad eating condition.
(V) Injection method
It is mainly used for spawning and anti-inflammation for parent fish generally by injection at chest, abdomen and back muscle.
(VI) Smear method
It is used for wound inflammation of parent fish by using gentian violet or iodine.
II. Calculation of Pond Water Volume
All-pond spraying method is adopted. At medication, we must accurately calculate the pond water. Thus, we should first measure the length, width and depth. In case of circular ponds, we should measure the radius and then calculate the volume by the following formula.
Pond volume (m3) = length (meter) * width (m) * average depth (m)
Circular pond water volume (m3): 3.14* (pond radius) square * depth
It should be noted that generally the square pond has a certain slope, and its cross section is trapezoidal. When calculating the volume, its length and width should be measured according to 1/2 of bottom of the pond.
III. Calculation of Dosage
All-pond spraying method dosage (g) = water volume (cubic meters) * drug concentration (ppm)
Dipping dosage (g) = amount of water (cubic meters) * impregnant concentration (ppm)
Oral dosage (g) = pond fish-containing capacity (kg) * fish medication dosage (g/kg body weight)
Preparation concentration of mixed feed (%) = dosage / (fish-containing capacity * daily feeding rate) * 100%
Section V Types of Common Fish Medicines and Incompatibility
I. Types of common fish medicines
Environment improver: The drugs used to improve the breeding water environment, including sediment improver, water improver and other ecological improvers, such as quicklime, zeolite, etc.
Disinfectant: drugs used to kill harmful micro-organisms (including harmful protozoa) in water, such as bleaching powder, potassium permanganate and so on.
Anti-microbial drugs: it refers to drugs orally or by injection to kill or inhibit the reproduction and growth of pathogenic microorganisms, including anti-viral drugs, anti-bacterial drugs, antifungal drugs, such as tetracycline, compound sulfamethoxazole and so on.
Pesticides and anthelmintic drugs: it refers to drugs by bath or orally to kill or expel the parasites in vitro or in vivo as well as drugs to kill harmful invertebrates in water, including antiprotozoal drugs, anti-worm drugs and anti-crustacean animal medicines, such as copper sulfate, trichlorfon and so on.
Metabolic improvement and enhancement drugs: it refers to drugs for improving the breeding object metabolism, enhancing the physical body, promoting illness recovery and promoting the growth. They are usually used in the way of food additives, such as vitamin C, phosphate, and methionine and so on.
Chinese herbal medicines: it refers to processed or raw medicinal plants (or animals) for prevention and control of aquatic animal and plant diseases or improvement of health of breeding objects, and they are also known as natural drugs, such as rhubarb, Andrographis paniculata and so on.
Biological products: it refers to medicament made through biochemistry and biotechnology, usually with special function, including vaccines, immune activation agents, certain hormones, diagnostic reagents, biological water purification agents and so on.
Others: including antioxidants, anesthetics, preservatives, synergists and other drugs for secondary effects, such as sorbic acid, tert-butyl hydroxyanisole and so on.
II. Common Fish Drug Incompatibility
In the process of aquaculture production, fish drugs have their safety range and synergy and antagonism function. We should pay attention to fish drug incompatibility, which is vital for right medication, improvement of efficacy, reduction of side effects and reduction of treatment cost.
Drug safety range: it refers to the range between the minimum effective dose and the maximum tolerated dose. Good drugs have a greater safety range, and in this range, the role increases with increase of dose. However, the dose is related with aquatic animal species, age, health status and environmental factors (such as temperature, pH, organic content, etc.) etc.. Therefore, the specific application dose must be within safety limit.
Synergy refers to strengthening of function due to mutual assistance of two or more drugs.
Antagonism refers to weakening of function due to mutual cancellation of two or more drugs.
For safe and effective use of fish medicine, fish drug incompatibility should be noted in the production.
Quicklime: it can not be mixed with bleaching powder, calcium, magnesium, heavy metallic salts, organic compounds and so on.
Bleaching powder: it can not be mixed with acid, formalin, quicklime and so on.
Potassium permanganate: it will be deoxidized, decolored and be invalid in case of mixture with organic matters such as glycerin, alcohol and so on; and it may explode in case of mixed with glycerol and medicinal tannic acid, and it may suffer flocculent precipitate in case of mixed with ammonia and its preparations.
Bromogeramine: it is quaternary ammonium surfactant. It can not be mixed with iodine, potassium sulfonate, sodium peroxide, oxidizer, soap, detergent and other surfactants.
Iodine and its preparations: they will generate explosive sulfonate in presence of ammonia and ammonium salts, generate iodate in presence of alkali, form yellow precipitate in presence of with heavy metal salts, be oxidized and bleach in presence of sodium thiosulfate and tannic acid, turn blue in presence of alkaloids, be less effective in presence of gentian violet, break down and loss effect in presence of volatile oil and fatty oil, show antagonism in presence of some furan drugs, and be reduced in absorption in presence of basic drugs, anticholinergic drugs and H2 receptor blockers.
：与碱性药液如 ST 注射液
Penicillin: it will gradually loss effect in presence of the alkaline liquid such as ST injection, decompose and loss effect in presence of acidic drugs such as tetracycline, oxidant, loss effect in presence of oxidizer, iodine, potassium permanganate and hydrogen peroxide solution and heavy metal salts such as copper, mercury, lead and so on.
Oxytetracycline: it will loss effect in presence of neutral and alkaline solution.
Chlortetracycline: it will loss effect in presence of compound iodine solution.
Tetracycline: it will loss effect in presence of alkaloid; it can not be mixed with chlorine disinfectants; and it will decompose and loss effect in presence of volatile oil and fatty oil.
Copper sulphate: it will generate a blue precipitate in presence of ammonia solution, generate dark brown precipitate in presence of tannic acid and its preparations, and generate dark blue precipitate in presence of alkaline liquid.
Trichlorfon: it can not be mixed with the alkaline solution; after placement for a long time it will gradually decompose and loss effect; and it will loss effect when mixed with atropine and celphos due to antagonism.
Section VI Common Diseases of Tilapia and Clarias Fuscus and the Prevention & Control
I. Common diseases of Tilapia and The Prevention & Control
Etiology: streptococcal infection.
Disease symptoms: for diseased fish suffering from hemolytic streptococcus, there will be black body color, exophthalmos, bleeding and spotting bleeding inside the gill cover. Fish suffering from non-hemolytic streptococcus will show exophthalmos, abdominal ascites accumulation, redness around the anus and intestinal atony.
Prevention and control methods: ① to avoid too close breeding and strengthen management; ② to spray pure chlorine dioxide at dosage of 0.3 to 0.5g/cubic meter in the whole pond for disinfection in case of diseases; ③ to feed allicin for 3 to 5 days, and then spray enzyme-added probotics after the fifth day at dosage of 0.5 to 0.8 g/cubic meter in the whole pond .
Motile aeromonas disease
Disease symptoms: it is divided into enteritis type and ulcerated surface type. Enteritis type mainly shows anal swelling, redness of the skin around the anus, intestinal no blood but redness. Ulcerated surface type shows surface patchy ulceration throughout the body, surface congestion, flake off, muscles exposure, red patchy lesion and festering into serious caves. Thus, it is also known as ulcer disease.
Etiology: Aeromonas hydrophila infection.
Prevention and control methods: ① spraying the whole pond with Bromochlorodimethylhydantoin at dosage of 0.2 g/cubic meter or bleaching powder (chlorine content 28% ~ 30%) at dosage of 1g /cubic meter once every other day for three times. ② At the same time, feeding allicin and other internal medicine.
Symptoms of the disease: the appearance symptoms include exophthalmos and abdominal swelling. According to dissection observation, abdominal ascites exist. In the bladder, kidney and spleen, there are white nodular lesions, and there is yellow pus in bladder cavity. These are typical symptoms. Diagnosis requires the use of bacteriological or serological tests.
Etiology: fluorescence Pseudomonas infection.
Prevention and control methods: ① this bacteria only infects unhealthy and weak tilapia, so we should strengthen management, maintain good water quality, pay attention to sanitation and be careful in operation so as to prevent fish from injury; ② for sick fish Bromochlorodimethylhydantoin is sprayed at dosage of 0.4 to 0.5 g / cubic meter; ③ at the same time, feeding the immune polysaccharide 10 g / kg feed and vitamin C 5g/kg feed.
Edward coli disease
Symptoms of the disease: the sick fish show black body color, abdominal swelling, anal redness and exophthalmos. In addition, some diseased fish body surface can show expansion inflammation parts, and the tail fin, anal and dorsal fin suffer necrosis and are white. According to dissection observation, we can see ascites, gonad and especially ovarian bleeding, intestinal water-like material or intestinal congestion. Liver, spleen, bladder and other internal organs, especially liver, have white nodular lesions and smells foul. Symptoms and course of disease are very different due to the different cases, and are divided into acute and chronic type.
Etiology: slow Edward coli infection.
Prevention and control methods: ① stocking density should be reasonable, and ponds need cleaning and disinfection as well as fresh water injection; ② spraying the whole pond with bleaching powder (chlorine content 28% ~ 30%) at dosage of 1 g /cubic meter; ③ feeding with garlic orally (mixed with feed at 5%) or allicin and other drugs once a day for 3 days.
Causes and symptoms of the disease: Long-term feeding of low-protein, high-fat and high-carbohydrate diets lack of vitamins will cause fat metabolism disorders to tilapia so that a lot of fat will accumulate to result in low resistance to disease. Diseased fish suffer systemic fat cell proliferation and fatty infiltration, and particularly abdominal fat tissues and fat tissues around the organs increase significantly. Suffered fish belly cavity fat tissue weight is up to 5% to 8% of the body weight, and liver is yellow, with a high degree of fatty degeneration and liver cell atrophy. If the entire tissue is cut and placed in water, the liver will float at the water (normal liver will immediately sink to the bottom). The suffered fish has low disease resistance capability and are easy to be infected with Escherichia coli and aeromonas.
Prevention and control methods: ① improving bait formulations to meet the needs of normal growth of tilapia; adding vitamin B, vitamin C and vitamin E and some natural feed to bait; ② strengthening management to keep the water clean and fresh.
Trichodiniasis: the pathogens are trichodina and small trichodina, with great harm on tilapia fry.
Symptoms: sick fish’s head and parts around the mouth are pale, the body surface and gills have more mucus. In case of a large number of infected fish, diseased fish loss appetite, have difficulty in breathing, solitude, travel independently and swim slowly. If they are not promptly treated, it may result in a large number of deaths. By microscopic examination, the body surface and gills of diseased fish show a lot of trichodina scrolling.
Prevention and control methods: ① spraying copper sulfate at dosage of 0.5 g per cubic meter and ferrous sulfate mixture at dosage of 0.2 g per cubic meter in the whole pond to kill Trichodina on fish surface and gills. ② spraying the whole pond with 30 kg of boiling China tree leaves per mu (1 meter depth) over the entire pond.
Etiology: autoeciousness of Dactylogyridae Monogenea on the gills of fish.
Symptoms: Dactylogyridae hooks the gill filaments by grasp and small edge hooks to move constantly, resulting in gill tissue damage. Diseased fish gills show more mucus, gill swelling, black color and failing to feed. The disease is often complicated with trichodiniasis and may cause death of a large number of Tilapia in serious case.
Prevention and control Methods: spraying 0.3 mg/l crystal "trichlorfon" to the whole pond once a day for 2 consecutive days.
Gyrodactyliasis: the pathogens are medium, fine and beautiful Gyrodactylus.
Symptoms: They can parasitize adult fish, fry and fish seeds, with great harm to the fish seeds. The fish seeds with Gyrodactyliasis first show extreme anxiety, sometimes madly swim in water or swim at lower water and then loss appetite, swim slowly, become thinner and finally die
Prevention and control methods: spraying the whole pond with (90%) 0.2 ~ 0.3 mg /l crystal trichlorfon.
II. Common Diseases of Clarias Fuscus and The Prevention & Control
(I) Prevention and control of infectious fish diseases
Putrid skin disease
Pathogens: bacteria infection.
Symptoms: skin inflammation, oval ulcer ring and eventually printed spots. In severe case, bone can be exposed.
Prevention and control methods: spraying 0.1-0.3ppm furazolidone in the whole pond and orally feeding fish with streptomycin bait at dose of 20,000 units per kilogram of fish.
Pathogens: bacterial diseases.
Symptoms: abdominal swelling, yellow mucus out of the abdomen, anal swelling, ventral erythema and borer fins. According to dissection, we can see intestinal congestion and inflammation.
Prevention and control methods: regularly spraying 30-40ppm quicklime to prevent the disease; in terms of treatment, 17g furazolidone can be added to every 50kg feed as bait, or adding 250g of garlic and 250 g of salt to every 50kg feed; and spraying 2-3ppm gall in the whole pond.
Pathogens: Aeromonas punctata furuncuLe
Symptoms: running sore full of pus in affected muscle.
Prevention and control methods: spraying 1ppm bleaching powder or 2ppm gall in the whole pond for disease prevention; in case of disease attack, spraying drugs in the whole pond and at the same time, mixing bait with sulfathiazole to feed fish at dosage of 10g of sulfathiazole, 2g of tmp, 0.6g of prednisone and 10 g of soda tablets per 100kg fish on the first day, and then reducing the dosage to a half for the second to sixth day.
Pathogens: bacteria infection.
Symptoms: abnormal activity, with head up and tail down vertically and still, fin congestion, abdominal swelling, lateral and intestinal bleeding.
Prevention and control methods: spraying furazolidone or other antibacterial drugs in the whole pond, and feeding fish with oral drug bait at dosage of 10g of oxytetracycline and 2g of tmp per 100 kg of fish for 3 to 6 days.
(II) Prevention and control of parasitic diseases
Pathogens: Trichodina autoeciousness.
Symptoms: thin and black body, traveling alone, rotation, failure and death. By microscopic examination, we can see a large number of Trichodina.
Prevention and control methods: spraying 0.7ppm copper sulfate or mixture of copper sulfate and ferrous sulfate (5:2) in the whole pond; when it is difficult to accurately measure water volume, drug can be sprayed every 24 hours for twice to realize good effect and safer result.
Symptoms: no obvious symptoms in early stage; and in severe case, weight loss, black body color, swimming slowly, breathing difficulty, light blue or blue-gray mucus layer on surface, pale red gills and skin congestion and inflammation.
Prevention and control methods: using 0.05% formalin for baptism of diseased fish for 20-30 minutes; and the treatment method is the same as that for Trichodiniasis.
Pathogens: Epistylis autoeciousness.
Symptoms: proliferative white spots on body surface and fins, in severe case, erosion of parasitic parts and blood stains.
Prevention and control methods: the same as that for Trichodiniasis.
Pathogens: Myxosporida autoeciousness.
Symptoms: white spot cysts on surface, thin and black body, sluggish activity. Microscopic examination shows that there are a lot of sporozoons in the cysts.
Prevention and control methods: using 15-30ppm formalin for baptism of diseased fish for 30-60 minutes for 7 days.
Symptoms: curling of tentacles, black body color, much mucus, loss of appetite, thin body to death. Through careful observation by the naked eyes, we can see hair-like worms in lesions.
Prevention and control methods: spraying 0.3-0.5ppm concentration of 90% of crystal trichlorfon in the whole pond.
Symptoms: much mucus on gill surface, dark gray or pale gills, shortness of breath. Through careful observation, we can see white Dactylogyridae in it. In severe case, gill cover will open and fish will die.
Prevention and control methods: the same as that for Gyrodactyliasis.