What are the treatment methods for several diseases of large yellow croaker?

I. White spot disease (cryptocaryoniasis) 1. Pathogen: Cryptocaryon irritans, also known as "marine fish ichthyophthirius," belongs to the ciliate class of the phylum Ciliophora. The body is oval or spherical, with uniform cilia over its entire surface.

2. Symptoms: The parasite mainly infests the body surface, gills and fin rays of the large yellow croaker. In the early stage of the disease, white spots are visible to the naked eye on the caudal and pectoral fins of the diseased fish, and as the disease progresses they gradually spread to the body surface and gills, with the increasing white spots forming a film, commonly known as "white spot disease." The diseased fish are restless, either swimming in circles along the pond walls, or leaping and darting out of the water, or rushing against and rubbing the pond walls; in severe cases the scales fall off, the muscles become inflamed and ulcerated, the eyes turn cloudy white, appetite declines, the body becomes emaciated, and movement slows; finally, because the gill tissue is severely damaged, the fish have difficulty breathing and die of suffocation.

3. Epidemiology: It is most prevalent from mid-March to August each year, at a water temperature of 15-30°C. In hatchery rooms at a water temperature of 25-30°C, especially for fry more than 20 days old, it is most likely to occur when the pond water exchange volume is less than 4/5, and it spreads rapidly with a high mortality rate, capable of causing total mortality within 1-2 days.

4. Prevention and treatment methods: 1) Preventive measures: ① For pond and hatchery room culture waters, increase the water exchange volume, improve water quality, and disinfect regularly; the sand filter pond should be regularly splashed with formalin for disinfection and parasite control.

② Hatchery room utensils should be frequently soaked and disinfected with formalin or potassium permanganate, and each pond should have its own dedicated utensils.

③ The spread rate of the parasite increases with the stocking density of the fish, so the stocking density should not be too high.

④ In daily management, nutrition should be strengthened and complete feed fed to improve the disease resistance of the fish.

2) Treatment methods: ① Bathe the diseased fish in 0.6-0.7 mg/L CuSO4 for 12-18 hours, or in 10 mg/L CuSO4 for 10-20 minutes; after a large amount of mucus has been discharged, siphon off the waste from the whole pond and carry out a complete water exchange or transfer the fry to another pond. The fry survival rate is about 70%.

② Bathe the fry in 20-30 mg/L formalin for 20-24 hours, then carry out a complete water exchange or transfer to another pond.

③ Bathe the fry in 100 mg/L formalin for 3-5 minutes, then move them to a clean seawater pond. With timely treatment, the cure rate can generally reach 70-90%.

④ Soak in 50 ppm Shachongling for 5-8 minutes.

⑤ Hanging bags of blue and white tablets: Crush the blue tablets (Shachong No. 1) and white tablets (Nongkangbao No. 1), wrap them in 60-mesh bolting silk netting, and hang them at the four corners of the fry pond at a depth of 30 cm underwater. For a 50 m3 fry pond, hang 2-4 tablets at a time; never feed at the places where the medicine is hung, and when siphoning waste and changing water, the medicine bags should be taken up.

II. Enteritis 1. Pathogen: This disease is mainly caused by infection with various species of Aeromonas hydrophila and Vibrio, etc. It is mainly due to feeding stale or spoiled bait, incomplete disinfection of the environment and feeding utensils, and overfeeding that causes the fish to eat too much.

2. Symptoms: In the early stage of the disease, the diseased fish has a darkened body color, swims alone away from the group, and loses appetite. Later symptoms are abdominal swelling and reddening and swelling of the anus; the gills of the diseased fish lose blood and turn white; necropsy shows congestion and inflammation of the intestinal wall, ulceration and sloughing of the intestinal mucosa, and the intestinal tract filled with pale yellow liquid, with water accumulation.

3. Epidemiology: It mainly occurs during the spring fry breeding stage; the prevalent season is April to September, and the peak incidence is at the relatively high water temperature of 25-30°C. The course of this disease is relatively short, and it can cause mass mortality within 3-5 days, with a mortality rate of over 50% in severe cases.

4. Prevention and treatment methods: Drug bathing is strictly prohibited for treating this disease. ① Maintain good environmental hygiene and disinfect feeding utensils before each use.

② The bait should be fresh, and feeding should avoid sudden increases or decreases.

③ Control the feeding amount during high-temperature periods: it should be controlled at 70-80% satiation, and never feed to full satiation.

④ When the disease is prevalent, add 2-4% allicin to the bait and reduce the number of meals and the amount fed, and if necessary, temporarily stop feeding.

III. Benedeniasis 1. Pathogen: The pathogen is Benedenia, a type of monogenean trematode; the body is elliptical and flat, white, 6-7 mm long, and visible to the naked eye.

2. Symptoms: The parasite infests the mouth, eyes, body surface, fins and other parts of the fish, appearing white and transparent, the size of a sesame seed, which is why some people also call it "white sesame disease" or "termite disease." When there are many parasites, they appear as white patches; the parasite attaches to the fish skin or under the scales, ingests the epithelial cells and blood cells of the fish, and causes wounds to the fish body. The diseased fish secretes excessive mucus on the body surface, is restless, and continuously swims wildly or rubs against the net walls, causing the scales to fall off and leading to infection. The diseased fish's appetite decreases, and finally it dies from emaciation and exhaustion. The body surface of dead fish is ragged, with increased mucus, fallen scales, damaged eyes, incomplete fin rays, dark red gills, and an emaciated body. Soaking the diseased fish in fresh water for a few minutes makes the parasites fall off.

3. Epidemiology: The prevalent season is September to November. During the autumn fry rearing stage, it often causes mixed infections with Cryptocaryon irritans and Ancyrocephalus, worsening the condition; if not treated in time, it can cause mass mortality within a short period.

4. Prevention and treatment methods: ① The most effective method is to bathe the diseased fish in fresh water for 20-40 minutes, carried out in three sessions, each lasting about 10 minutes.

② Bathe in 150-200 ppm formalin for 20-30 minutes.

③ Feed erythromycin medicated bait at 3-5% of fish body weight for 5 consecutive days.

④ Soak in 30 mg/L oxytetracycline for about 10 minutes, and repeat once after one week.

IV. Valvular body disease 1. Pathogen: The pathogen is Piscinoodinium-like stone flounder valvular parasite (Benedenia-like). In the middle of its body, slightly to one side, there is a large oval nucleus, and there are clustered cilia at the anterior part and the anterior edge of the dorsal side. The parasite can swim rapidly in water by means of the beating of the cilia.

2. Symptoms: The valvular parasite infests the body surface, fin rays and gill filaments of the fish, causing increased mucus secretion; the gills become anemic and grayish white, the gill filaments swell, and many mud-like impurities adhere to them; irregular white patches also appear on the body surface. Appetite decreases and food intake is greatly reduced; the diseased fish swims slowly away from the group, its body color becomes lighter, and it has difficulty breathing, soon dying in large numbers due to physical debilitation.

3. Epidemiology: This disease is prevalent from April to June, and the peak incidence is when the water temperature is above 25°C; it is a relatively harmful parasitic disease. It mainly harms small fry with a total length of 20-50 mm bred in late spring and early summer. This disease comes on quickly, has a short course, and has high infection and mortality rates; if not treated in time, it can cause mass mortality, and the daily mortality rate of this disease can reach over 10%.

4. Prevention and treatment methods: ① Soak in a 200-250 ppm formalin seawater solution for 20 minutes; during soaking, control the density at 25-35 fish/L and aerate to increase oxygen.

② Prepare furazolidone with fresh water at a concentration of 20 mg/L, and soak the diseased fish for 3-5 minutes.

③ Prepare copper sulfate with seawater at a concentration of 2 mg/L, and bathe the diseased fish for 10-20 minutes.

④ After soaking, add 20-30% antibiotics (such as tetracycline, erythromycin, etc.) to the bait and feed for 5 days until recovery.