Diagnosing Fish and Shrimp Diseases by Color and Disease Prevention and Treatment Methods

After fish and shrimp become ill, a certain part of their body or a certain organ takes on a distinctive color, which becomes a characteristic symptom of the disease they are suffering from. Animal medicine workers use this to name the disease for identification, prevention and treatment. This is a commonly used method in the animal medicine field, briefly described as follows:

1. "Red" diagnosis

(1) Eel red spot disease is caused by Pseudomonas anguilliseptica, mainly harming Japanese eels; European eels are not easily infected. Symptoms: pinpoint hemorrhages appear on the lower jaw, operculum, base of the pectoral fins and the body surface of the abdomen, with death occurring within 1 to 2 days. Necropsy: pinpoint hemorrhages on the peritoneum. Treatment: (1) Tetracycline: 1 gram per kilogram of bait per day, fed in 2 divided doses, for 3 to 10 consecutive days. (2) Bleaching powder: at a concentration of 1.3 mg/L of pond water, dissolve and remove the residue, then splash over the whole pond. Prevention: Before fingerlings are put into the pond, bathe them in 3% salt water for 5 to 20 minutes.

(2) Fish red-skin disease is caused by Pseudomonas fluorescens, and grass carp, black carp and common carp are easily infected. Symptoms: small or large areas of hemorrhage, inflammation and scale loss on both sides and the abdomen of the fish body; in severe cases, hemorrhage at the base of the fins, rotting at the ends of the fins, congestion of the upper and lower jaws and operculum, presenting patchy red spots, with death in 8 to 10 days. Treatment: (1) Bleaching powder: 1 gram per cubic meter of water, applied to the whole pond. (2) Sulfathiazole sodium: mixed into bait and fed, 5 grams per 50 kg of body weight on the first day; from the 2nd to the 6th day, 2.5 grams per 50 kg of body weight per day. Prevention: Before fingerlings are put into the pond, use bleaching powder at 5 to 10 grams per liter of water and soak for half an hour.

(3) Shrimp red-body disease is caused by Taura syndrome virus, and Pacific white shrimp are easily infected. Symptoms: in acute cases, the body surface is pale red, and the tail fan and swimming legs are dark red. In chronic cases, only black spots appear on the shrimp shell surface. Prevention and treatment measures: (1) Bromochlorohydantoin: 0.5 mg/L of water, splashed over the whole pond. (2) Isatis root 50 grams and Sanhuang powder 200 grams, mixed into 100 kg of bait and fed for 1 consecutive week.

(4) Shrimp red-gill disease is caused by a certain Vibrio species (such as Vibrio marinus, Vibrio anguillarum, Vibrio parahaemolyticus, etc.). Symptoms: in the early stage, the gills and appendages are red, and in the later stage the whole body is red; the two sides of the shrimp body are white, and the abdomen is turbid white. Treatment: (1) Oxytetracycline: 0.5 grams per kilogram of bait, fed for 5 consecutive days. (2) Bleaching powder: 3 mg/L of water, splashed over the shrimp pond for disinfection. Prevention: (1) Frequently add fresh water to the shrimp pond to improve water quality. (2) Ensure sufficient dissolved oxygen in the shrimp pond.

2. "Yellow" diagnosis

Shrimp yellow-gill disease: also known as shrimp yellow-head disease, it is caused by shrimp yellow-gill disease virus. Symptoms: the gills are pale yellow, and the body color is pale. Necropsy: the liver and pancreas are pale yellow. Treatment: Bromochlorohydantoin: 0.3 mg/L of water, splashed over the whole pond. Prevention: Dijundu: 0.5 mg/L of water, splashed over the whole pond.

3. "White" diagnosis

(1) Fish white-head white-mouth disease is caused by Myxococcus, mainly occurring in grass carp, and occasionally in other fish such as silver carp, bighead carp and black carp. Symptoms: while in water, the skin from the forehead and around the mouth to between the eyes is mildly ulcerated and appears white. After leaving the water, the symptoms are not obvious, and only a few fish show white-head white-mouth symptoms, with a relatively high mortality rate. Treatment: (1) Qingfengmycin: 25.0 grams per 50 kg of body weight, mixed into bait and fed for 4 consecutive days. (2) Furazolidone: ① 5 to 10 grams per 50 kg of body weight, mixed into bait and fed. ② 0.1 to 0.2 grams per cubic meter of water, splashed over the whole pond. Prevention: (1) Keep the pond water clean. (2) Reduce stocking density.

(2) Fish white-skin disease is caused by Pseudomonas dermoalba, mainly harming silver carp and bighead carp, while ricefield eels are less susceptible. Symptoms: white spots and white patches appear at the base of the dorsal fin and on the caudal fin, gradually expanding until the dorsal fin and the whole body become white. In some cases the caudal fin is incomplete; diseased fish stand upside down in the water with the head down and tail up, occasionally struggling to swim, and die in 2 to 3 days, with a mortality rate of 10% to 20%. Treatment: (1) Junduling: 0.45 to 0.75 grams per cubic meter of water, splashed over the whole pond. (2) Bleaching powder: 1 gram per cubic meter of water, splashed over the whole pond. Prevention: (1) Keep the pond water quality good. (2) Do not injure the fish body during handling.

(3) Fish white-fuzz disease is caused by Saprolegnia or Achlya, mainly harming grass carp, and other freshwater fish can also develop the disease. Ornamental tropical fish kept by a certain Xing in Jinan City, Shandong Province once suffered from this disease. Symptoms: the fungal body invades through wounds, with one end of the hypha extending into the muscle and one end exposed on the body surface. The exposed part multiplies and branches profusely, becoming white cotton-like, with a relatively high mortality rate. Treatment: (1) Malachite green 66 grams per cubic meter of water, bathe for 5 to 10 minutes. (2) Add 0.4 kg of sodium chloride and 0.4 kg of sodium bicarbonate per cubic meter of water; after dissolving, bathe the diseased fish for half an hour. Prevention: (1) Do not injure the fish body during routine handling. (2) Keep the water body clean at all times.

4. "Black" diagnosis

Shrimp black-gill disease: caused by long-term lack of Vc in shrimp and contamination of the shrimp pond. Symptoms: the gills first become light red, then dark red, and finally turn black, with difficulty breathing and death soon after. Treatment: (1) Immediately replace the shrimp pond with clean water. (2) Vc 100 mg, mixed into 100 grams of bait and fed. (3) Furazolidone: 2 mg/L of water, bathe, suitable for cases caused by bacteria. (4) Potassium permanganate: 10 mg/L of water, splashed over the whole pond, suitable for cases caused by fungi. Prevention: Regularly add new water to the shrimp pond to keep the water quality clean; disinfect regularly; regularly remove sludge.