Author: Yin Lunfu
Recombinant trematodes belong to the order Trematodes of the order Trematodes, and live parasitically throughout the camp. There are many kinds, different sizes, forms, and living habits, and the insect body can be smaller than 0.5 mm, and the largest can reach more than 10 cm. It is generally flattened leafy or ovate, kidney-shaped, etc. With suction cups. Intermediate hosts need to be replaced during the course of life history. The intermediate hosts are mollusks gastropods and flap gills, link animal polychaetes, aquatic insects, plants and fish. Compound flukes are widely distributed, common parasites in fish, its infection rate is high, spread fast, treatment is difficult, the harm to fish farming is extremely great, and may also directly endanger human health. Especially in recent years, with the frequent circulation of aquatic products and the enhancement of parasitic resistance, the area of recolored trematodiasis hazards continues to expand, and the types and quantities of cultured fish infected with diseases have increased year by year, it is necessary for the majority of fishery disease prevention and control workers and farmers to understand recolored trematodiasis, and take reasonable prevention and control measures in the production process to prevent its spread and reduce economic losses.
First, the diagnosis of major complex trematodiasis
1 Compound trematodiasis
(1) Epidemic and hazard
It is also called double-hole compound fluke disease, which is endemic from May to August and occurs throughout the country, especially in areas with more gulls and cones. It can harm most farmed fish, causing mass seed deaths in acute infection and cataract symptoms in chronic infection.
(2) Cause of incidence
Caused by double-hole flux cysticers of the recombinant fluke species. The double-hole fluke tail larvae escape in the water, and when they encounter the second host fish, they quickly bite and burrow into the body, enter the eyeball through the circulatory system or nervous system, and develop into cysticer after about 1 month.
(3) Symptom recognition
In acute infection, the sick fish swim and struggle on the surface of the water, and then swim slowly, sometimes swimming rapidly on the surface of the water, and the movement is out of control. The most notable symptoms are congestion of the head, a bright red color around the orbit, and the diseased fish die soon after. In chronic infection, the above symptoms are not obvious, pathogens can accumulate a lot in the orbit, causing the crystals to be cloudy and whitish, and in severe cases, the entire eye is blind or the crystals fall off, resulting in inability to eat normally, thin and dead.
2 Hematosis
This is a worldwide fish disease, there are reports of a large number of deaths of sick fish everywhere, almost all freshwater and marine farmed fish, often causing large numbers of deaths of fry and fish species.
(2) Diagnostic methods
The disease is easy to be misdiagnosed or missed, the correct inspection method is: (1) the heart and arterial bulb of the diseased fish are taken out, put into a Petri dish containing normal saline, cut open the heart and arterial bulb, and gently scrape the inner wall, in a bright place with the naked eye, you can see whether there is an adult schistosomiasis; (2) press the relevant tissue into thin sheets, check whether there are a large number of orange valve eggs under the microscope, especially to carefully examine the gills and kidney tissue; (3) find out whether there are a large number of intermediate parasites (snails) in the fish pond.
Schistosomiasis is acute and chronic. The acute type is that the density of tail crickets in the water is high, and in a short period of time, multiple tail crickets drill into the fish, causing the fry to jump, struggle, swim sharply on the surface of the water, or suspended on the surface of the water uh water, the gills are swollen, the gills are open, the entrance is blistered, the whole body is red and swollen, the gills and body surface mucus increase, and soon die. The chronic type is a small number of tailed larvae that burrow into the fish body scatteredly. The worm body develops into an adult worm in the heart movement pulse of the fish, the worm eggs are carried with the blood to the liver, spleen, kidney, mesentery, muscles, brain, spinal cord, gills, etc., the worm eggs on the gills can develop and hatch larvae, causing bleeding and gill tissue damage, worm eggs that are brought to other tissues, outsourcing multi-layered connective tissue, when the number is large, can cause blood vessels to be blocked, tissue damage, corresponding symptoms, generally in the kidneys there are more eggs, kidney tissue damage, causing water in the abdominal cavity, protruding vertical scales, enlarged protrusion, and gradually failing to die.
3 Lateral trematodiasis
The disease mainly endangers fish fry and summer flower fish species, grass, green, silver carp, mandarin fish, etc. can occur, can cause a large number of deaths, the middle and lower reaches of the Yangtze River has been scattered cases.
(2) Pathogenesis
The disease is caused by fry swallowing snails containing lateral fluke certils, which develop into adult worms in the intestines of fish. Therefore, the pathogenesis conditions are: the fry pond has been farmed with adult fish, but the pond has not been completely cleared to kill the snails; the water quality of the fry pond is too old, lack of natural palatable bait, or insufficient feeding. The disease mostly occurs in the fry rearing phase in May.
The diseased fish do not eat, the growth stops, the swimming is weak, and it floats with the wind in the downwind place of the fish pond. Place the fry directly under a microscope, or dissect the diseased fish and remove the intestine, where the intestine is filled with trematodes.
3. Prevention and control measures
1 precautions
(1) Thoroughly clear the pond
Before breeding, the fish pond should be thoroughly cleared, and quicklime or "chlorinide" (dosage 1 kg/mu) can be applied to disinfect to eliminate the middle parasite, and sand silk should be filtered when entering the water to prevent the intermediate host from being brought in with the water.
(2) Seed quarantine
When purchasing seedlings from other places, it is first necessary to understand whether the area is a re-breeding trematode epidemic area, and secondly, it is necessary to quarantine carefully and not to buy seedlings without quarantine certificates. Fry in the lower pond before the thorough disinfection, many farmers like to use salt disinfection, in fact, salt on the pathogen killing power is limited, it is best to choose the ingredient for povidone iodine fishing drugs, such as "Yufeng iodine", the dosage of 5-10 g / cubic meter of water, medicinal bath 20-30 minutes, the compound trematodes have a strong killing effect.
(3) Booby trap snails
In the evening, the grass can be tied into several small bundles into the pond to trap, and the bale is fished out early the next morning, shake off the snails attached to it and buried deeply; if the pathogen is already in the water body, the crystal enemy insects should be sprinkled throughout the whole pool at the same time to kill the tail clypses in the water, and the number of sprinkles is determined according to the effect of trapping the middle parasite in the pool and the intensity and infection rate of the insect body in the snail.
(4) Drug prophylaxis
If in areas with a high incidence of re-breeding trematodiasis or in ponds where the disease has occurred in previous years, during the onset of the disease, high-efficiency insecticides such as "insect lijing" and "fish and insect extermination" are regularly used to sprinkle the whole pond to prevent the occurrence of tail crickets in the water body.
2 treatment methods
(1) Inverted pond isolation and temporary rearing
That is, the diseased fish are placed in ponds without compound flukes and intermediate host snails for culture. If possible, the sick fish can be placed in indoor ponds for temporary rearing, and depending on the degree of infection, they can be cared for in separate ponds. For the more seriously infected sick fish, salt water is taken to protect the fish, and the concentration is controlled at 0.1% to 0.3%. After more than a month of nursing, the sick fish can basically return to normal.
(2) Medication
Use "spore killing" to feed according to the amount of 250 g/100 kg of feed mixture, twice a day, for 3-5 days.
(3) Adjuvant therapy
These include booby-trapping intermediate host snails, sprinkling insecticides, and referring to preventive measures.