Detailed Explanation of Key Technical Points for Disease Prevention and Control in Mandarin Fish

Mandarin fish, also known as gui fish, osmanthus fish, ao fish, ji hua fish, pang gui, etc., is distributed only in the rivers and lakes of the eastern plains of China. In winter it overwinters in deep water, and in spring it swims toward shallow areas. It hides by day and comes out at night, and is fierce in nature. Young fish prefer to eat fish and shrimp, while adult fish feed mainly on fish. It stops feeding in winter. Artificial breeding has now been achieved. Let us take a look at the disease prevention and control techniques for mandarin fish below!

Saprolegniasis

[Cause of onset] During the reproduction of mandarin fish, if the water used for hatching fertilized eggs is mixed with debris, the fish eggs will be damaged and thus become infected with water mold. In infected fish eggs, a downy substance can be seen growing outside the egg membrane with the naked eye, similar to the saprolegniasis of "home fish" eggs, and in severe cases it can cause mass death.

[Characteristics of onset] With the naked eye, white flocculent material can be seen on the body surface and abrasions of diseased fish. Once infected with this disease, the diseased fish swims slowly, has reduced appetite, and finally becomes emaciated and dies.

[Prevention and control methods] 1. Filter the hatching water for mandarin fish with a 60-mesh nylon gauze to prevent debris from entering. 2. Splash with 0.01% malachite green solution, stop the water for 3 to 5 minutes, 2 to 3 times a day; or splash with 2% salt water and stop the water for 5 minutes. 3. Do not select injured fish as broodstock. Before the broodstock are placed in the pond, smear the fish body with 1% malachite green ointment or an appropriate amount of sulfonamide ointment. 4. At the fry, fingerling and adult fish stages, soak and wash with 3% salt water for 5 to 10 minutes, or soak and wash diseased fish with 1% salt water plus a few drops of vinegar for 5 minutes. In addition, during fishing and transportation, prevent abrasions to the fish body.

Ciliate disease

[Characteristics of onset] Ciliate disease is one of the main diseases during the summer fry cultivation of mandarin fish, mainly caused by Trichodina and similar organisms parasitizing the body surface, fins and head of mandarin fish. The disease spreads rapidly. When the number of parasites is small, it has little effect on the fish's activity; when the number of parasites is large, the fish refuses to eat. With the naked eye, white dot-like substances can be seen on the fish body, the mouth cannot close, swimming loses balance, and then death follows. This disease is extremely harmful.

[Prevention and control methods] 1. For flowing-water ponds, splash the entire pond once a day with 3% salt water and stop the water for 3 to 5 minutes, which can have a preventive and therapeutic effect. 2. For flowing-water ponds, splash the entire pond with a mixture of 1.6×10-6 copper sulfate and ferrous sulfate (5:2) and stop the water for 3 to 5 minutes, with obvious curative effect; for still-water ponds, splash the entire pond with 0.7×10-6? copper sulfate and ferrous sulfate (5:2) mixture. 3. When summer fry are placed in the pond, soak and wash diseased fish with 2% salt water for 2 minutes.

Lernaea and Sinergasilus disease

[Characteristics of onset] Lernaea mainly parasitizes the body surface of mandarin fish, causing the fish body to become emaciated and lose the ability to swim and prey. Sinergasilus mainly parasitizes the gills, destroys gill tissue, and affects respiratory ability. These copepods mainly harm mandarin fish fingerlings and are relatively harmful. If 2 Lernaea parasitize the body of a 5 cm young fish, it can cause the death of the young fish, so early prevention should be taken in aquaculture.

[Prevention and control methods] 1. Before releasing seedlings and fingerlings, the pond should be cleared with quicklime with water, which can kill the copepods in the water, and attention should be paid at all times to the cleanliness of the water source and feed to reduce sources of infection. 2. The bait fish for mandarin fish can be soaked and washed with 15 mg/L potassium permanganate for 2 hours, which can eliminate the copepods on the fish body. 3. For mandarin fish, soak and wash with 5 mg/kg crystal trichlorfon solution for 5 minutes, or splash the entire pond with ?0.5? mg/kg crystal trichlorfon, both of which can make the copepods on the fish body fall off.

Gill rot and enteritis

[Characteristics of onset] The disease mostly occurs in high-temperature seasons. The gill filaments rot with white spots, and debris and mucus are attached.

[Prevention and control methods] For gill rot, soak and wash with a 2 mg per liter mercurous nitrate solution for 10 minutes, which can gradually relieve the condition. The main symptoms of enteritis are congestion and swelling from the rectum to the anus, with pale yellow feces. In severe cases, the entire intestinal tract swells and appears purplish red, and the excrement is thick liquid. The cause is mainly that bait fish carrying bacteria are swallowed by mandarin fish. Therefore, the prevention method is to disinfect the bait fish, soak and wash the fish body with 10% salt water, and promptly remove diseased and disabled bait fish to eliminate sources of infection.

Argulosis

[Characteristics of onset] Sinergasilus parasitizes the body surface, fins and gills of mandarin fish. With the naked eye, worm bodies the size of bedbugs can be seen. They often use their barbs to pierce the fish body they parasitize, causing the diseased fish to show symptoms of frantic swimming and restlessness.

[Prevention and control methods] Same as the prevention and control methods for gill rot, or splash the entire pond with crystal trichlorfon (90%) so that the pond water concentration reaches 0.3×10-6 to 0.5×10-6, which can cure this disease. When preventing and treating mandarin fish diseases, note that mandarin fish are very sensitive to drugs, especially trichlorfon. The concentration used must be strictly controlled; too high a concentration will cause fish death.

Trichodiniasis

[Inducing pathogen] Many species in the two genera Trichodina and Trichodinella.

[Characteristics of onset] Diseased fish swim frantically in groups along the pond edge, do not feed, and the body becomes thin, commonly known as "horse-racing disease." A layer of white film sometimes appears on the fish body surface.

[Diagnostic method] Place small fish under a dissecting microscope for observation. A large number of Trichodina can be seen on the body surface of the diseased fish, especially on the head and fin rays. This is "large Trichodina." Take a small amount of gill filaments and observe under a microscope. A large number of Trichodina are found densely piled on the gill filaments, destroying gill tissue and seriously affecting gill respiration. This is mainly "small Trichodina."

[Harm characteristics] It is prevalent in aquaculture farms across the country, especially in the Yangtze River and Xijiang River basins. Each year from May to August is the epidemic season for this disease, especially June to July, which is the season of frequent occurrence. This disease is extremely harmful to mandarin fish fry and fingerlings and is one of the most harmful diseases during the fry and fingerling cultivation stage of mandarin fish, especially most likely to occur under dense culture conditions.

[Prevention and control methods] Within 10 days after the fry hatch, soak the fish body with a 7 ppm copper sulfate and ferrous sulfate (5:2) mixture for 10 minutes, once a day. At other stages, splash the entire pond with 0.7 ppm copper sulfate and ferrous sulfate mixture (5:2), with relatively significant curative effect.