Latin name: Other names: Pathogen: bacteria
Fish are inert,
Fish do not react to anything,
Fish do not take food very well (low appetite),
Fish go to vertical position,
Fish hang near the surface,
Fish stop feeding,
Darkening of body color (Black discoloration),
Degradation of gills,
Fraying of fins,
Protruding operculi (gill covers),
Ragged or frayed dorsal fin,
White and gray nodules (spots),
Severely affected fish will without showing any pathological changes (the superacute form). The acute form of the disease when the gill apparatus and skin get affected is most common. Asphyxia is observed in cases where gills are affected. Fish show loss of appetite or stop feeding altogether. Other signs are grayish mucous spots which are most commonly seen near the dorsal or caudal fins. Spots begin to ulcerate. Fins begin to disintegrate and denudation of the muscles can be observed. In some fish, gills become severely affected. Sick fish float at the water surface gasping for air, rapid gilling is observed. Fish become lethargic, float vertically, do not respond to external irritants. Other symptoms to look out for are darkening of the skin and excessive slime production. Fish show rapid breathing and ‘coughting’. The gill covers stick out and pale-rose or hyperemic filament can be seen beneath them. In advanced stages, clamped gill filaments and necrosis are observed. Pathogens causing saprolegniosis can be seen in areas of necrosis. Another symptom is disintegration of the dorsal fins which manifests itself as soft tissue necrosis.
Myxobacterioses are common bacterial freshwater fish diseases which affect gills and skin. They are caused by the bacteria Flexibacter and Cytophaga, gram nagative, rod- shaped, motile bacteria, measuring 3 to 8 micron long by 0.3 to 0.5 micron wide. Myxobacterioses are subdivided into: Flexibacteriosis Bacterial gill disease Bacterial cold-water disease
Flexibacteriosis (columnaris) All cultivated fish are susceptible to this disease. Flexibacteriosis is especially dangerous for young Salmonidae and Cyprinidae. It is caused by Flexibacter columnaris from the family Cytophagaceae. The bacterial clumps form characteristic columns on the medium and on the fish. Fish get infected by both high- and low-virulent strains. The former usually affect gills. They have the incubation period of 24 hours. The disease progresses rapidly and causes catastrophic losses (acute disease). Fish often do not show any external signs of infection. The latter affect the skin, causing lesions; the mortality rate is lower (chronic disease). The incubation period is variable: from 48 hours to a few weeks depending on water temperatures. Affected fish show loss of appetite or stop feeding. Symptoms include grayish mucous spots which appear most commonly near the dorsal or caudal fins. Spots begin to ulcerate. Fins will deteriorate and denudation of muscles can be observed. Affected fish will float at water surface gasping for air and open gill covers.
Bacterial gill disease (BGD) The disease is caused by the bacterium Flexibacter branchiophila which is present in water, soil, and on the bed of fishponds.
Gills become affected which causes thickening of the gill epithelium, melting and thickening of gill filaments. In the acute from, large amounts of bacteria that appear within a short period of time impair breathing. The incubation period is variable: between 24 hours to several weeks. In acute cases, the disease is asymptomatic and fish die showing no external signs of infection. In the chronic form, fish swim at water surface gulping for air, become lethargic, swim vertically, do not respond actively to external irritants. Fish show an excess of mucous, skin darkening. Affeted fish stop feeding. Other signs to look out for include increased reparation and coughing motions. Gill covers are open, beneath them pale-rose or bright red gill filaments can be observed. In advanced stages, affected fish will show clamped gill filamentss; necrosis will develop. Pathogens causing saprolegniosis can be seen in areas of necrosis. Another symptom is disintegration of the dorsal fins which manifests itself as soft tissue necrosis.
Bacterial Cold Water disease affects mainly fish farms with Salmonids, though can also affect other species. The disease is caused by Cylophaga psychrophila. Larvae, which do not yet float, show yolk coagulation and erosion of epidermis of the yolk sac. Larvae mortality rates increase by 50 %. Fry fish show skin darkening and characteristic lesions which appear as white spots. In young-of-the-year fish, the disease manifests itself as erosion of the dorsal and caudal fins, hyperemia of the anus, necrosis of the dorsal fin and tail-fin with the skeleton and mandible exposure. One-year-old fish show skin disintegration and musculature becomes exposed on the head, jaws, and other parts of the body. Affected fish will exhibit anemia and hemorrhages in the gills and stop feeding. The mortality rate among fry, young-of-the-year and one-year old fish is 10-20%.
Myxobacteria may be the cause of secondary infections as they infect open wounds and penetrate into the musculature of affected and traumatized fish.
Myxobacteria are most commonly observed at high temperatures and in unkempt aquarium conditions (injuries, stress, poor diet, low aterechange, overcrowding, etc).
How to cure:
For treating the disease it is recommended to use either trypaflavine (in the main tank – 0.8g per 100L, for 14 days; in a separate tank - 0.2g per 10L, for 20 minutes, six times) or copper sulphate (in a separate tank – 1g per 10L, for 15-20 minutes, seven times; use copper sulphate in chemically or analytically pure form).
Fish with Flexibacteriosis and Bacterial gill disease should be given the following baths: a 5 to 10 minute bath in 1-1.5 g/m3 of potassium permanganate; furasolidone (for BGD - 12,5 mg/l for 20 minutes; for Flexibacteriosis -50 g/l for 5 days).
Prevention of Cold Water disease includes treating breeding stock with antibiotics before the spawning period, treating eyed eggs with Iodinolum (concentration of 1:10, for 10 minutes with pÍ not higher than 7.5 once); Flowage should be increased and depth should be lowered in the tank where the larvae are kept. In the early stages, it is recommended to give affected fish baths of the antibiotic oxytetracycline (10-50 mg/L, for 20 minutes), alternating them with potassium permanganate baths (2 g/m3, for 1 hour). Baths are given for three days. If white spots start to appear on the body fish should be given baths with one of the following medications: chloramine B (100 mg/L, for 1 hour, daily for 7 days); furasolidone (7.5 mg per 100L of water, for 4-6 hours; daily for 7 days). If sick fish do not stop feeding, add oxytetracycline to the feed at 50-70 mg/kg of feed for 10 days.
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trypaflavine copper sulphate potassium permanganate furasolidone oxytetracycline chloramine B
Maintain clean water; do not overcrowd the tank, do not share equipment.
Fish susceptible to the disease/disorder:
Young fish are most susceptible to the disease, however all ages may be affected.