Whether fish suffer from scale protrusion or fin rot, neither should be taken lightly.
Fin rot is the most common disease in ornamental fish; the slightest decline in water quality shows up on the fish right away. Scale protrusion has a low incidence rate, and many fish keepers may never have encountered this disease, but if both conditions occur at the same time, it is truly worthy of sympathy. So today we will discuss these two major diseases in detail.
Scale
Protrusion
Disease
Scale protrusion disease, also known as lepidorthosis, pinecone disease, or pine scale disease, is caused by Aeromonas caviae. It is a fish disease in which, after the fish body is injured and becomes infected, fluid accumulates in the scale pockets, causing the scales to stand up. From larger fish to broodstock (referring to male or female fish that have developed to the stage of sexual maturity and have reproductive capacity, also called seed fish), all can be infected. It mainly harms larger broodstock. Scale protrusion disease is prevalent in some countries in Europe and Asia. It frequently occurs in fish-farming areas in Northeast China, North China, East China, and other regions. It is mainly prevalent in static water fish tanks/ponds and occurs less often in flowing water fish ponds. The occurrence and spread of this disease appear in low-temperature seasons, especially when the temperature drops suddenly. It often occurs in late winter and early spring, that is, after overwintering ponds thaw and during the initial period of fingerling stocking, as well as in late autumn and early winter, that is, after fingerlings are placed in overwintering ponds and before the ice seals over. The mortality rate is generally above 50%, and the mortality rate of carp broodstock can reach as high as 85%.
Disease factors
The pathogen is initially considered to be Aeromonas caviae. Aeromonas caviae can cause hemorrhagic septicemia at high temperatures and scale protrusion disease at low temperatures. When water quality is turbid, the fish body has mechanical injury or frostbite, and the fish's disease resistance is weak, infection occurs through the skin.
Main symptoms and pathological changes
In the early stage of the disease, the fish body darkens. The body surface is rough, the scales on the front part of the fish stand up, and the scale pockets contain translucent fluid. Sick fish swim alone away from the group and move slowly. In severe cases, they have difficulty breathing, lose response to external stimuli, and float at the water surface. In severe cases, the whole body's scales stand up, the scale pockets contain bloody exudate, and when the scales are gently pressed with a finger, the exudate spurts out from under the scales, and the scales fall off along with it. Sometimes there is congestion at the fin base, with translucent fluid between the fin membranes; when stroked with slight force in the direction parallel to the fin rays, the fluid spurts out.
The eyeballs protrude, the abdomen becomes distended, and a large amount of ascites accumulates in the abdominal cavity. Sick fish are anemic, and the colors of the gills, liver, spleen, and kidneys all become pale. The inner epidermis of the operculum is congested. This disease is relatively intuitive: sick fish with small scales have a body resembling a file, while sick fish with large scales have a body resembling a pinecone. As the disease progresses, sick fish have difficulty breathing, become anemic, lose body balance, either turn upside down or turn belly upward, swim slowly and weakly, and die after lasting two to three days.
Diagnostic points
Based on typical symptoms, such as standing scales, protruding eyeballs, distended abdomen, ascites, fluid in the scale pockets, and exudate spurting out when the scales are gently pressed, a preliminary judgment can be made. Microscopic examination of the exudate in the scale pockets, showing large numbers of Gram-negative short bacilli, can provide further diagnosis.
Prevention and control measures
1. Preventive measures
Strengthen the fish's constitution; mix 0.3-0.6 g of vitamin E per 10 kg of fish body weight into artificial feed daily. Long-term use can effectively prevent this disease. Scale protrusion disease is caused by infection after injury to the fish body surface, so during production operations such as catching, transportation, grading, and stocking, care should be taken to avoid injury to the fish body. For stocking, soak the fish body in 4% salt water for 5-10 minutes.
2. Treatment
(1) Soak sick fish in a mixed solution containing 2 g of salt and 3 g of baking soda per liter of water for 10-15 minutes.
(2) Oral norfloxacin: 0.8-1.0 g of medicinal powder per 10 kg of fish body weight per day, once daily, for 6 days, mixed into artificial feed and fed.
(3) For diseased broodstock, streptomycin sulfate can be injected at 15-20 mg per kg of body weight; gently press and break the edematous blisters of the scale pockets without causing the scales to fall off, wipe with 10% warm salt water, then apply iodine tincture, and inject streptomycin sulfate intramuscularly, which has obvious effects.
(4) Oxytetracycline hydrochloride
Prevention: 0.5-1 g per 100 kg of fish body weight made into medicated bait, once daily, for 3 consecutive days;
Treatment: 2-5 g per 100 kg of fish body weight made into medicated bait, fed once daily, for 3-7 consecutive days.
(5) Add 200 g of florfenicol per 100 kg of feed, feed once daily, for 3-5 consecutive days.
Notes on diagnosis and treatment
Scale protrusion disease involves large numbers of short bacilli. In goldfish, scale protrusion disease should be distinguished from normal pearl scales. The scales of pearl-scale goldfish have calcareous deposits and are glossy, giving a beautiful impression. Sick fish with scale protrusion disease have dull scales, and the sick fish usually sink to the bottom or lose body balance.
Fin
Rot
Disease
Fin rot disease is a disease caused by bacteria and characterized by the caudal fin rotting and falling off. This disease can occur in all four seasons, and fish from the current year to spawning broodstock can all suffer from it. It is more harmful to ornamental fish varieties with thinner caudal fins.
Disease factors
The pathogens of fin rot disease differ among different fish species. These include Aeromonas hydrophila, Aeromonas sobria, marine Flexibacter, Aeromonas hydrophila subsp. anaerogenes, and Aeromonas sobria infection, among others. These bacteria are all opportunistic pathogens and widely exist in water bodies. When water quality deteriorates, climate changes, scales fall off, skin is damaged, nutrition is poor, the fish's disease resistance decreases, or parasitic diseases occur, infection is likely.
Main symptoms and pathological changes
Main symptoms and pathological changes: This disease mostly occurs in ornamental fish varieties with thinner caudal fins, especially commonly in pearl gouramis. The symptoms are initially not obvious and hard to notice. When the fish floats at the surface, careful observation may reveal spot-like white spots on the caudal peduncle. As the disease progresses, feeding decreases, fin rays become congested, scales on the caudal peduncle fall off, and symptoms such as inflammation, congestion, and muscle necrosis and decay appear. The caudal fin and caudal peduncle become congested and inflamed, the ends of the fin rays become milky white and eroded, and in some cases the connective tissue between the fin ray cartilages splits open, appearing like a broken broom. In severe cases, the caudal fin can rot away, the caudal peduncle muscles ulcerate, and the bones become exposed.
Due to rotting, the fin rays become incomplete. The fish body often loses balance, swims alone away from the group, alternately floating and sinking, with the head tilted downward and the caudal fin obliquely exposed at the water surface.
Key points to note
A preliminary diagnosis can be made based on characteristic symptoms such as congestion of the fin rays, destruction of interfin tissue, separation of fin rays, erosion of the fin ray tips, and in severe cases ulceration of the caudal peduncle muscles or even rotting away of the entire tail.
Prevention and control measures
1. Preventive measures
(1) During the aquaculture process, always maintain a good water environment. This is especially true for earthen cement pond culture, which has poor self-purification capacity, so even more attention should be paid to regular water disinfection to prevent excessive reproduction of Aeromonas sobria in the water.
(2) In summer, increase water transparency and provide appropriate shading to prevent tail scalding.
(3) All operations involving the fish body should be carried out carefully and cautiously to avoid injuring the fish body and fish mucosa.
(4) Remove parasites promptly to prevent parasitic bites from injuring the fish body.
2. Treatment
(1) For diseased broodstock, inject 80,000 international units of penicillin per chapter appendix (dilute each vial with 1.5-2.0 mL of physiological saline) or 0.5 g of cefradine into the pectoral (abdominal) fin.
(2) Sprinkle strong chlorine powder throughout the pond at a treatment concentration of 0.4-0.5 g per cubic meter of water. At the same time, use this drug to make medicated bait and feed it at 60 g per 100 kg of fish body weight, once daily, for 3 consecutive days. If part of the caudal fin has rotted and become incomplete, cut it off with scissors to make the fin rays even, then treat with the above drugs. Usually after 10-15 days, the split fin rays can heal, and the cut-off parts can regenerate, but the regenerated fin rays will leave a trace with the old fin rays.
Notes on diagnosis and treatment
1. For differential diagnosis, pay attention to distinguishing it from red-skin disease.
Fin-eroding fin rot disease shows symptoms in sick fish such as congestion of fin rays, destruction of interfin tissue, separation of fin rays, erosion of fin ray tips, and in severe cases ulceration of the caudal peduncle muscles or even rotting away of the entire tail, hence the name fin rot disease. Another type of fin erosion is caused by Pseudomonas fluorescens. The fin tips of sick fish rot, the soft tissue between fin rays is destroyed, making the fin rays appear broom-like, and sick fish are also accompanied by body surface inflammation and scale loss. This disease is also called red-skin disease.
2. Drug use
When this disease occurs, injecting sensitive antibiotic drugs is the key to curing the diseased fish; the disease is also called red-skin disease. In addition, this disease very easily occurs concurrently with fungal diseases and other bacterial diseases, so attention should be paid to identification and targeted control measures should be taken. No matter what treatment plan is adopted, before handling, thoroughly remove waste so that the fish tank/pond water is clean. After handling, promptly use photosynthetic bacteria and water conditioners or active bacteria to treat the water quality. Only in this way is it possible to avoid recurrence within a few days after fin rot disease is cured. At the same time, during medication, the concentration and duration should be determined according to water temperature, pH, the size and constitution of the sick fish, and attention should be paid to frequently observing the activity of the sick fish and adjusting the treatment plan in time.
That is all for the above content. I hope it can help everyone. If there are any shortcomings, I hope the seniors will offer guidance.