Prevention and Treatment Methods for Common Diseases in Large Yellow Croaker Aquaculture

Benedenia Disease

[Cause] The disease is caused by parasitism of Benedenia.

[Symptoms] Benedenia often parasitizes various parts of the body surface of marine fish such as large yellow croaker, yellowfin seabream, @#@240@#@, black seabream, and grouper, especially the front half of the back. When Benedenia parasitizes the fish body, the fish are restless in the water, constantly swim frantically, rub against nets or pond walls; the large and small hooks of the worm's posterior attachment disc tear the epidermis, causing wounds and inflammation on the body surface, secreting large amounts of mucus; in severe cases, anemia, emaciation, localized or large-area ulcers on the body surface, or complications such as rotten jaw and rotten tail.

[Treatment]

Method 1: Freshwater immersion bath, soaking for 15-20 minutes at a water temperature of 10-20°C, 10-15 minutes at 20-25°C, and 5-10 minutes above 25°C. This method is labor-intensive, the fish body is easily injured during operation, and severe cases can cause massive fish death; moreover, injured fish after soaking are prone to complicating with rotten jaw and rotten tail disease. After soaking, one tablet of "Fuchlor Type 1" can be hung in each cage to kill bacteria in the water and prevent wound infection, while "Fish Health No. 1-2000" is orally administered at an inclusion rate of 2%.

Method 2: Trichlorfon hanging bag. Currently, the more commonly used method is the trichlorfon hanging bag, but the biggest characteristic of this method is that the trichlorfon concentration is difficult to control; too high a concentration easily causes fish poisoning and death, while too low a concentration cannot kill Benedenia. Poisoning and death accidents are most likely to occur during the high-temperature summer season.

Method 3: "Yuchongqing No. 2" hanging bag, which can expel Benedenia from the fish body. One week later, hang one tablet of "Fuchlor Type 1" in each cage, which can treat complications of rotten skin and rotten tail; when complications are severe, "Fish Health No. 1-2000" can be orally administered at the same time. This method is safer, more reliable, more labor-saving, and more convenient than the previous two methods, with better deworming effects. Fish diseases caused by other helminths such as Anchoradens and Gyrodactylus can also be treated with this method.

White Spot Disease (Cryptocaryon irritans disease)

[Cause] The disease is caused by parasitism of Cryptocaryon irritans on the fish body.

[Symptoms] It mainly parasitizes the body surface, gills, and other parts of large yellow croaker. The fish body is covered with small white spots visible to the naked eye, commonly known as white spot disease. When there are many parasites, it can cause breathing difficulty, rotten gills, and rotten skin. Diseased fish float on the water surface, which can cause mass mortality. It is especially harmful to fry and fingerlings, and infection is more likely during the fry rearing stage.

[Prevention]

1. Stocking density should not be too high; 2. Disinfect the fry rearing pond regularly; for cages, "Fuchlor Type 1" can be hung in bags.

[Treatment] Bath with formalin at 15-20 ppm for 12 hours, then change the water; after changing the water, orally administer 2% "Fish Health No. 1" or "Fish Health No. 1-2000" to prevent secondary infection; at the same time, use "Fuchlor Type 1" hanging bags to disinfect the water body.

Trichodiniasis

[Cause] Caused by massive parasitism of Trichodina.

[Symptoms] The parasitic sites are the fish body surface, fins, gills, and other parts, especially the gills, where it is more common and severe. The parasite attaches to gill filaments and body surface with its attachment disc and keeps rotating. The teeth and hooks of the parasite can cause shedding and proliferation of gill epithelial tissue, excessive mucus secretion, respiratory impairment, and even rotten gills. Feeding gradually decreases, the fish becomes emaciated, and death may result.

[Treatment]

1. Bath the diseased fish with formalin at 25 ppm for 15-20 minutes.

2. Soak with "Yuchongqing No. 2-2000" at 0.4-0.5 ppm for 15-20 minutes, or splash at 0.15-0.2 ppm.

3. After treatment by any of the above methods, use "Fuchlor Type 1" hanging bags in combination, and orally administer "Fish Health No. 1-2000" at the same time, which can treat or prevent secondary infection.

Vibriosis

[Cause] Caused by infection with Vibrio anguillarum.

[Symptoms] The main characteristic is the formation of ulcers on the fish body. In the early stage of the disease, the lower jaw and caudal peduncle become red; in severe cases, the lower jaw ulcerates and is defective, the caudal peduncle ulcerates deep into the muscle, and the caudal fin ulcerates.

[Prevention] Hang 1 tablet of "Fuchlor Type 1" in each cage to kill bacteria in the water, once every two weeks. Usually, "Marine Fish Multivitamin" and "Special Vc for Aquaculture" can be added to the feed to strengthen nutrition and improve immunity.

[Treatment] Hang 1 tablet of "Fuchlor Type 1" in each cage, and orally administer "Fish Health No. 1" or "Fish Health No. 1-2000" according to the dosage in the instructions.

Bacterial Enteritis Disease

[Cause]

1. Disease outbreaks caused by infection with various Aeromonas hydrophila and other bacteria.

2. During storage of chilled fresh fish, proteins decompose to produce histamine, which combines with free lysine to produce "scombrotoxin," causing intestinal ulcers and erosion.

[Symptoms] Diseased fish leave the group and swim alone, the fish body becomes dark, appetite decreases, and eventually they stop feeding completely. When the intestine is cut open, the intestinal wall is locally congested and inflamed; there is no food in the intestinal cavity, or a small amount of food in the posterior intestinal segment, and there is more mucus in the intestine. In severe cases, the intestine appears purplish-red due to congestion, the intestinal wall has poor elasticity, there is a large amount of pale yellow mucus in the intestine, and the anus is red and swollen.

[Prevention]

1. Strengthen feed management and control the quality of feed fed.

2. Add 5 grams of "Fish Health No. 1" or "Fish Health No. 1-2000" and 5 grams of "Marine Fish Multivitamin" per kilogram of feed, and feed continuously.

[Treatment] Hang 1 tablet of "Fuchlor Type 1" in each cage; add 20 grams of "Fish Health No. 1" or "Fish Health No. 1-2000" and 2 grams of "Special Vc for Aquaculture" per kilogram of feed, and feed continuously for 3 days. In severe cases, medicated feed should be fed continuously until cured, then fed for another 2 days to consolidate the efficacy.

Liver Enlargement and Necrosis Disease

[Cause]

1. Caused by bacterial infection such as Streptococcus.

2. Caused by feed poisoning. It is caused by feeding spoiled and deteriorated feed. After poisoning, the body remains intact and the body color is normal; the fish float near the water surface or swim frantically until death.

3. Caused by feeding large amounts of antibiotic drugs.

[Symptoms] Diseased fish swim slowly, are scattered in slow-flow areas, and float on the water surface. The diseased fish have dark body color, white gills, congested, enlarged, and protruding eyeballs, and one or more swellings on the body surface, especially on the tail, where the swollen parts bleed or ulcerate; the anus is red and swollen. Necropsy reveals an enlarged liver with mottling and even necrosis, gastrointestinal effusion, and inflammation of the intestinal wall. Some have no obvious symptoms on the body surface, but the liver is locally or extensively necrotic and enlarged, with yellow fluid in the intestine. Mortality is highest during the fingerling stage.

[Prevention]

1. During the peak season of the disease, add 5 grams of "Fish Health No. 1" per kilogram of feed and feed continuously, while using "Fuchlor Type 1" hanging bags.

2. Strictly prohibit feeding deteriorated feed.

3. When the disease occurs, use the right medicine for the condition. Do not use the same antibiotic for a long time; continuous use of one antibiotic generally should not exceed 5-6 days to avoid drug resistance.

[Treatment]

1. Add 10 grams of "Yugankang" and 5-10 grams of "Marine Fish Multivitamin" per kilogram of feed (add 5 grams for fish paste, 10 grams for powder and pellet feed), and feed continuously for 3-5 days.

2. If feed quality is poor, replace the feed immediately, and at the same time add "Marine Fish Multivitamin" to the feed at the dosage above.

The above are the most common diseases in large yellow croaker aquaculture. In addition, there are nutritional diseases, precocious puberty, and other diseases, and certain results have also been achieved through treatment practice in recent years.

Nutritional Deficiency Disease

[Cause] Caused by a single feed type, incomplete nutrition, and deficiency of multiple vitamins, among other reasons.

[Symptoms] The fish body surface is dark or normal, the fish is emaciated, and some have protruding eyes and slow growth. Most diseased fish suffer from fatty liver syndrome. If stimulated by external factors such as sudden water quality changes, temperature drops, or netting, their stress capacity is poor, and mass mortality may occur. Splashing irritating bactericides and insecticides can also cause death.

[Prevention] Add Marine Fish Multivitamin to the feed over the long term, adding 5 grams of "Marine Fish Multivitamin" per kilogram of feed.

[Treatment] Add 10 grams of "Marine Fish Multivitamin" and 3 grams of "Special Vc for Aquaculture" per kilogram of feed, and continuous feeding can treat this disease.

Drug Poisoning Syndrome

Some farmers, due to lack of knowledge about drug use, misuse drugs during fish disease treatment, causing fish poisoning. The main situations are as follows:

1. After fish disease occurs, using large doses of antibiotics or multiple insecticides, etc., will cause reduced feeding or no feeding in fish.

2. Excessive use of trichlorfon. Most farmers use trichlorfon hanging bags to treat parasitic diseases, but trichlorfon is highly toxic; in mild cases it causes large yellow croaker to stop feeding, and in severe cases it causes massive poisoning and death of fish. However, trichlorfon is ineffective against protozoans such as Cryptocaryon, Petalosoma, and Trichodina. It is recommended not to blindly use organophosphorus insecticides such as trichlorfon.

3. Excessive use of trichlorfon in surrounding water bodies. Some farmers experience mass mortality even though they have not used any drugs (small fish are especially sensitive). According to analysis, this may be caused by the large-scale use of trichlorfon in surrounding water bodies. Excessive use of trichlorfon can form high concentrations in local waters or form an oil film on the water surface. Due to the fluidity of seawater, it spreads to surrounding aquaculture waters. Once trichlorfon reaches a lethal concentration in a certain water body due to water flow, it will cause poisoning and death of fish in that area.

[Symptoms] The fish swim weakly, float on the water surface, do not feed or feed very little. If an oil film forms on the water surface, it blocks oxygen exchange, and small fry may also die from hypoxia.

[Treatment] Remove the trichlorfon hanging bags from the water body, use gauze to remove the oil film on the water surface, or splash a small amount of quicklime on the cage surface to remove the oil film, and increase the exchange of seawater in the cage. After the above measures are implemented, orally administer "Yugankang" and "Marine Fish Multivitamin" for treatment.