What are the sensory identification methods for fish diseases?

(1) Intestinal diseases

1. Hemorrhagic disease: The muscles, mouth, and bases of various fins are congested, especially the anal fin. After peeling off the skin, pinpoint hemorrhages in the muscles are visible; in severe cases, the entire muscle turns red. Sometimes the operculum, lower jaw, orbital area, and intestines of sick fish also show congestion; the gills lose their bright red color or become pale.

2. Enteritis disease: The anus is red and swollen; in severe cases, pressing the abdomen gently causes pus and blood or yellow mucus to flow from the anus, and part or all of the intestine is inflamed, appearing purplish-red.

3. Coccidiosis: The gill filaments are pale; in severe cases, the abdomen is slightly swollen, and the inner wall of the anterior intestine contains many rice-grain-like coccidian cysts.

(2) Skin diseases

1. Red-skin disease: The epidermis rots or the fin rays are eaten away and broken; the body surface is locally or largely congested and inflamed, and scales fall off, most noticeably on the abdomen.

2. Stamp disease: This disease rots inward from the outside. Round, oval, or elliptical red spots appear on the caudal peduncle or both sides of the abdomen of sick fish; in severe cases, the muscles rot and small holes appear, exposing bones or internal organs.

3. White-skin disease: The skin from the rear of the dorsal fin to the end of the caudal peduncle turns white, appearing like white mist and markedly different in color from the front half.

4. Furunculosis: This disease rots outward from the inside. Swollen abscesses appear on both sides of the back of sick fish and feel swollen to the touch. When the epidermis of the sick fish is cut open, the muscles appear purulent and bloody.

5. White-head and white-mouth disease: It often occurs in fry and early summer fingerling stages. Sick fish are thin and darkened, float near the shore, and the top of the head and area around the mouth turn white; in severe cases, rotting occurs.

6. Saprolegniasis: The body surface of sick fish grows fungal filaments resembling old cotton wadding, and eventually the sick fish become emaciated and die.

7. Trichodiniasis: The gills of sick fish are congested, the head turns red, and the area around the mouth is sometimes white. When the condition is severe, sick fish often gather in groups at the pond edge.

8. Chilodonelliasis: The body surface of sick fish has increased mucus, and a pale blue-gray film often forms on the surface.

9. Ichthyophthiriasis: The body surface and fins of sick fish are covered with small white dot-like pustules.

(3) Other diseases

1. Dropsy: The body surface of sick fish is rough, and some scales (mostly on the tail) spread outward like a pinecone, forming erect scales, with transparent fluid accumulating beneath the scales. Sick fish sometimes show symptoms such as exophthalmos, abdominal distension, and subcutaneous congestion near the fin bases.

2. Crazy disease: Sick fish are emaciated, with dull body color, and the rear half of the body tilts upward; they often swim in circles at the water surface. When the skull of the sick fish is opened, white dot-like myxosporean cysts can be seen.

3. Ligulosis: The abdomen of sick fish is enlarged; when the abdomen is cut open, colored ribbon-like worms can be seen in the body cavity.

4. Diplostomiasis: The brain of sick fish is congested, the mouth ring turns white, and the eyeballs protrude or even fall off. Some sick fish have cloudy, milky-white eyeballs.

5. Fish louse disease: There is a soybean-sized hole at the base of the pectoral fin of sick fish, and the parasite can be seen inside the hole.

6. Powder disease: The whole body of sick fish looks as if it is coated with a layer of rice flour.