Every summer and autumn, farmers of golden pomfret on the southeast coast are extra careful, because this is the time when the small melon worms in the seawater are active. In the past experience, the harm of seawater melon insects to guangxi's golden pomfret breeding industry is very large, and it will cause serious losses every year. According to the production area, at present, a small number of fish have been infected with small melon worms in Zhanjiang, Guangdong and Tieshan Port in Guangxi, and the infected fish are not normal and grow slowly. In September, there are more thunderstorms and typhoons along the coast of South China, and the water temperature and temperature are higher, which is the high incidence season of small melon insects, and farmers should do a good job in the prevention and control of diseases in advance.
First, the pathogen and life history
Seawater fish melon worm disease is also called seawater fish white spot disease, its pathogen is to stimulate cryptonuclear worms, that is, seawater melon worms, parasite taxonomy belongs to the protozoa phylum, ciliate subphylum, oligosylociliomerous suborder, membranous mouth suborder, notch family, cryptonuclear insect genus, parasitic seawater teleost fish skin, gills under the epithelium can cause infectious diseases of fish. Stimulating cryptonuclear worms are very similar to multi-soned melon worms, spherical or ovate, the whole body is cilia, the front end has a cell mouth, the diameter of mature individuals is 0.4 to 0.5 mm, the difference is that the large nuclei of the stimulating cryptonucleus are oval-shaped, 4 to 8, generally 4, connected in a candibal shape, the insect body transparency is low, the insect body under the microscope is gray-black, and it is difficult to see its large nucleus.
Microscopic stimulation of cryptonuclear insectoids
The life history of the seawater melon worm is divided into four stages: nourishing nutrients and encapsulated precursors, encapsulation stage and larval stage, and the camp directly develops the life history without the need for an intermediate host. The trophozoite is the stage that stimulates cryptonuclear worms to parasitize the fish body, using the host as a source of nutrition, leaving the host fish after maturity, falling on the bottom of the pool or other solids and forming a cyst. The cysts undergo many divisions and finally form many ciliary larvae, so the reproduction rate of small melon worms is very fast. Ciliated larvae break through the sac and swim rapidly in the water, meet the host and attach to it, burrow into the epithelial tissue, and resume the development and parasitic life of the vegetative body. The escape of the larvae generally takes place at night when there is no light, and if the host cannot be found within 24 hours, it will die on its own.
Life history of small melon insects in seawater (Picture quoted from "Scientific Fish Farming", No. 10, 2004 Intensive Breeding Process stimulates the comprehensive control of cryptonuclear worm disease, authors Li Anxing, Huang Wei)
2. Symptoms, epidemiology and diagnosis
Seawater melon worms first parasitized in the gills, skin, fins, mouth, nose, cornea and other places of seawater fish, in the initial incidence of fish on the back, each fin first appeared a small number of white dots, visible to the naked eye, so called white spot disease. In the middle stage, many small white dots and mucus of 0.5 to 1 mm appear in the infected parts such as the surface of the fish body, gills, and fins, and the epidermal congestion at the infected site is hyperemic, and the gills are pink due to anemia, and then rapidly infected, and in severe cases, the epidermis of the fish body forms a cloudy white film. Fish body discomfort, often with the pool bottom, pool wall friction, bump, late sick fish serious uneasiness, swimming around the box or jumping out of the water, constantly rubbing the body on the solids, the body surface secretes a large amount of mucus, due to epidermal cell proliferation to produce white small sacs; body surface secondary bacterial infection, inflammation ulcers; fin defects, split forks; white eyes become blind; gill epithelial hyperplasia, some gill tissue anemia or necrosis; sick fish body color black, emaciated, swimming abnormalities. Eventually, the sick fish died of suffocation due to damage to the gill tissue, difficulty breathing, and suffocation.
Golden pomfret suffering from cryptonuclear disease stimulating (quoted from the Agricultural Treasure Book)
Stimulating cryptonuclear worms parasitic on gill filaments (from the ocean and fisheries)
Cryptonuclear stimulating insects are common parasites in marine fish, which can infect almost all species of marine cultured fish, but in the south of China, it mainly harms grouper, yellow croaker, oval pomfret, cobia and snapper fish, with fast infection rate and high mortality, which can cause all the deaths of farmed fish within 1 to 2 days. The epidemic season is mainly in the spring and autumn, when the water temperature is 20 ~ 30 °C is the high incidence of small melon worm disease in the seawater, especially after the typhoon, the environment in the sea area changes greatly, and the fish body is more likely to erupt when the resistance of the fish body is poor. Marine areas that are rich in organic matter and have slow water flow, large aquaculture density, dense distribution of fishing rows, poor water exchange conditions, and fishing rows that are fed ice (frozen) fresh fish bait for a long time are most likely to erupt.
Diagnostic method Carefully remove the white spots on the gills or mucus on the surface of the body of the diseased fish, place them on a glass slide, add a few drops of seawater and cover it with a coverslip, and place it under the microscope to see a round or oval, ciliated insect body, slowly swimming in rotation, the insect body is large and opaque. This can basically be diagnosed as a seawater melon worm.
If there is no microscope, you can cut off the fins with small white spots, place them in a white porcelain dish containing seawater, in a good place, use 2 needles to gently break the membrane of the white spots, pick a few more in a row, if you see a small insect rolling out of the water swimming, you can make a diagnosis.
In the process of diagnosis, attention should also be paid to the difference between stimulating cryptonuclear worm disease and myxosporidosis: the white spots of fish with cryptonucleosomiasis stimulating cryptonucleosomiasis are spherical, the size is basically equal, the body surface mucus is more, and the swimming of cryptonuclear worms can be observed under the microscope; the white spots of the fish body of myxosporosis vary in size, some are lumpy, the mucus of the fish body is little or no, and the insect body swims, but the spores can be observed.
Third, prevention and control recommendations.
In the process of prevention and control of the disease of seawater melon insects, because the cage culture of seawater fish accounts for a large part of the proportion, cage culture belongs to the open water body, and when using external drugs, only the hanging bag method and the separation soaking method can be used, the operation is more troublesome, and the medicinal effect is also good in the closed water body. Moreover, if the stimulation of cryptonuclear worm disease is not found and treated in time, the number of parasites will rise sharply, which will lead to a large number of deaths of diseased fish. Therefore, it is necessary to adhere to the principle of putting prevention first.
(1) Prevention.
Stimulate the high incidence of cryptonuclear worm disease, feed some Chinese herbal medicines with insect repellent function and feed additives that improve the immunity and stress capacity of fish (such as astragalus immune polysaccharides, aquatic vitamin C, etc.). The specific scheme is as follows:
1 pack of fibrous (dried ginger mixed powder for fishing, etc.) or 1 pack of Cordyceps (artemisia annua, etc.) + 1 pack of Yerba Buena Sanhuang Powder + 50 kg of 50 kg of aquatic special vc20 grams of mixture for prevention, feeding 1-2 times a month for 3 days each time.
(2) Treatment
In the treatment process of seawater melon insect disease, it is necessary to find and deal with it in time. Because after the emergence of stimulating cryptonuclear worms, its number of increases requires a process, early treatment, the number of parasites on the fish body to control at a relatively low level is particularly critical, if the parasites parasitized in the fish body reach a certain number, the disease is more difficult to control, will lead to a large number of fish deaths.
The trophozoite stage of seawater melon worm can stimulate the host to form a sac, and the capsule precursor and the capsule stage have a thick cyst wall protection, the drug is difficult to penetrate, and the drug is poor in these stages. Only the newly hatched larvae are less resistant to drugs. Since the larval hatching time is usually at night, that is, midnight to early morning, it is best to use the drug at night to kill the larvae with relatively weak resistance.
1. Soak in fresh water. Half of the bath is 5-10 minutes, and you need to pay attention to the state of the fish during the bath. After treatment, the fish should gradually transition to the original salinity of the cultured water body, so as not to cause the fish to stress and die.
2, internal use of fibrosis (fishing dried ginger mixing powder, etc.) 200 g + cordyceps (artemisia annua, etc.) 200 grams of mixing 40 kg, external use of protozoal paste (dried ginger, pepper, etc.) hanging bag, continuous use for 5-7 days.