Latin name: Mycobacterium piscium Other names: Pathogen: bacteria
An autopsy reveals numerous nodules in the spleen, liver, kidney, heart, intestines, gills, muscles, sex glands, skin, eyes, and the skeleton. The nodules have a curdled consistency and are of brown or white color,
Fish are inert,
Fish do swinging movements,
Fish hide in secluded places,
Fish move in violent rushes,
Fish stop feeding,
Fish swing on their side,
Black discoloration of the iris,
Bloated front part of belly,
Brightening (lighting) of body colors,
Fish growth slows down,
Fish stop growing,
Fraying of fins,
Leukoma (spot on an eye),
Loss of eyes,
Overall body thinness,
Separation of fin rays,
Skin became transparent because of very enlarged belly,
Small dark spots,
Tail fin is down
Affected fish become sluggish, hide in the corners of the aquarium, swim with the caudal fin down, stop feeding, lie on one side on the gravel with the head and tail up. They show swaying movements, folded fins, emaciation, fading colors, eroding fin rays, bumps that turn into lesions, scale loss, ulcerous skin wounds, dark coloration of the iris, eye protrusion, and black spots all over the body. These symptoms may occur singly or in various combinations. If Tuberculosis is suspected, the liver and kidneys should be thoroughly examined. Through the magnifying glass and sometimes with the naked eye one can observe nodules of whitish to yellowish color. Microscopic examination will reveal pathogens. An autopsy will reveal numerous nodules in the spleen, liver, kidney, heart, intestines, gills, muscles, sex glands, skin, eyes, and the skeleton. These nodules have a curdy consistency and are of brown or white color. Examination of internal organs of Cichlids and Anabantidae will often reveal melanized tubercles (grainy black formations). They are from 60 to 200 micrometers in size. Later stages of mycobacteriosis are characterized by hardening and hyperplasia of thick connective tissue which fills in elements of affected areas (cirrhosis).
Tuberculosis is an infectious disease caused by Mycobacterium piscum. This is a gram-positive non-motile thick rod, between 2 and 12 micrometers in length. The optimum temperature for the bacterium growth on the nutritional media is 25C (77F). It affects fish’s internal organs. The disease strikes in epidemic proportions. The pathogen gets into the aquarium from a fish-pond with feed, plants and gravel if the latter has not been boiled or tempered as well as with fish, plants, water and equipment from a contaminated tank.
Depending on fish species, symptoms, pathologoanatomic changes they distinguish:
1. Mycobacteriosis of Macropodus 2. Dropsy (ascites) of Fighting Fish (Betta Splendens) 3. Pop-eye (Exophthalmia) of Danios 4. Clotted disease of cyprinoids 5. Exhaustion of Poeciliidae
Mycobacteriosis of Macropodus Infected fish show skin lesions, scale protrusion, loss of scales, a break in the integrity of the epidermis (outermost layer of the skin) and dermis (layer of skin beneath the epidermis that consists of connective tissue). Affected areas are inflamed, of reddish color. There are no hemorrhages. Fish will sometimes have conjunctivitis and pop-eye which cause blindness. Black spots appear in patches or cover the whole body of the affected fish. 8-30 days after skin lesions appear, fish’s abdomen begins to enlarge gradually and scale protrusion can be observed. The disease lasts between several days to several months and will eventually lead to death. An autopsy of all fish with these clinical signs will show severely affected kidneys which will be white and look bloated. On the surface, there will be a number of clotted nodules which vary in size from a pinhead to a pea. The liver will be of brownish-yellow and will partially have a curdy consistency. Fish with symptoms of ascites will have colorless, slightly cloudy liquid in the body cavity.
Dropsy (ascites) of Fighting Fish (Betta Splendens) Sick fish will gradually develop a swollen abdomen. Skin stretches and within 1-2 months becomes transparent. Scales begin to stick out. By this time abdomen will have a ‘pine-cone’ appearance. Affected fish become lethargic, stop feeding, hide in the corners of the aquarium, and often stay at the bottom. Then fish will show jerky, erratic movements. They swim on one side near the bottom or at the water’s surface with the belly up. At this stage, fish will usually die within a day. An autopsy will reveal a build-up of colorless, sticky, partly ‘curdy’ fluid. Internal organs will appear attached to the abdominal wall. Examinations will sometimes reveal small, ‘curdy’ nodules in the kidney and liver. Fighting Fish will die between 1.5 and 2 years of age.
Pop-eye (Exophthalmia) of Danios
The disease is prevalent during spawning in fish between 2 and 3 years of age. The abdomen becomes swollen, which is natural during spawning. Fish show no discoloration. Gradually, within two weeks, the eyes (sometimes only one eye) start bulging out of their sockets. Then one eye will burst and 1-3 days later the second one. Blind fish will die of exhaustion. An autopsy will show enlarged kidneys and liver covered with tiny (the size of a pinhead) curdy yellowish-white spots. Sometimes small ulcers will appear on the gills. An autopsy will reveal thick curdy white matter behind the eyeball which causes the eye to bulge.
Clotted disease of cyprinoids Only old fish are affected. Sick fish can live a long time and may not show any visible symptoms of the disease. The only characteristic sign of the disease is the swelling of the abdomen which has a ‘pine-cone’ appearance. An autopsy will reveal tambourine-like growths in the body cavity which spread to the walls of the abdomen and the whole of the left upper front part of the body behind the heart. These growths are cone-shaped with a blunt end. They can appear in other parts of the body cavity. Their dissection will reveal curdy matter separated into tiny parts. Separate formations about the size of a wheat grain or pea will be found in the body cavity and on the internal organs (the liver, kidney, spleen). These formations can grow separately or in groups affecting the peritoneum, frill, tissues of liver, kidneys, and spleen. The formations have a lard consistency.
Exhaustion of Poeciliidae
Affected fish show loss of appetite, constantly lose weight, and hide in the corners of the aquarium. They will have a curved spine, hollow belly, and sunken eyes. Bones protrude through the skin and scales. Fish will die within a month. An autopsy will not reveal any abnormalities in the internal organs. Sometimes there will be small yellowish granules (round grains) on the liver and kidneys.
The five clinical signs described above are not universal. Sometimes the disease may progress in a way not typical of a particular species. Male Congo suffering from Mycobacteriosis of Macropodus will have pop-eye, which often causes the eye to bulge out of its socket, whereas Pearl Gourami and Rainbowfish will have shallow ulcers all over the body and the tailhead as well as ‘cone-pine’ bumps in the front of the abdomen. Guppy will show ulcers, scale protrusion, and conjunctivitis.
Diagnosis is based on observation of clinical signs, pathologoanatomic changes, and microbiological examinations. To perform a microbiological examination, blood samples, ascitic fluid, and inoculations of ulcers, liver, kidney, spleen and tubercles, which form in the internal organs, are placed in the Petragnani media. Before inoculation, ulcers are rinsed with sterile physiological salt solution or boiled water. To exclude Ichthyosporidium disease, inoculations are also placed on gelatin, beef-extract (meat infusion) broth, agar with 1% blood serum.
The bacterium Mycobacterium piscium grows at 25C (77F) within 14-20 days. These bacteria appear in the from of dry, rough yellow-grey colonies. They die at temperatures above 34C (93F). To carry out microscopic examination, Ziehl-Neelsen staining of initial culture and culture of the bacterium is used. Microscopic examination will reveal characteristic bright red acid-fast rods.
How to cure:
Affected fish are destroyed. The tank and all equipment are disinfected with 1% B/T- chloramine solution (the bacterium is resistant to acid solutions) or chlorine solution containing no less than 5 % of active chlorine.
It is possible to try to treat valuable fish in a separate tank by adding into the water one of the following medications: doxycycline or monocycline (30mg per 10L) oxytetracycline (150mg per 10L) tetracycline (0.2g per 10L)
Treatment should be repeated after 1 month to ensure eradication. During the break in treatment water ozonation should be carried out in the tank containing the affected fish. The best treatment is to add kanamycin or rifampicin in the food (soak the bloodworm in a strong kanamycin solution (0.5-1g per 50-100 ml of water) for half hour, then give it to fish once a day. Concurrently, these medications can be added to the main/quarantine tank. If affected fish do not eat, remove them to a hospital tank for treatment and add medication into the water: kanamycin (3g per 100L), rifampicin (600 mg per 100 L of water). Antibiotics should be added into the water only in extreme cases, as they kill the beneficial nitrifying bacteria in the gravel and filter and therefore damage to biological equilibrium is inevitable. Improvements are observed within a week. After two weeks, fish look healthy and treatment should be terminated. For prevention, monthly perform 1-week treatments.
Prevention is through maintaining a healthy environment for your fish, providing them with a nutritionally balanced diet, avoiding overcrowding as well as maintaining high water quality. Quarantine new fish (especially the ones that come from abroad) for three months before intoducing them into the main tank. During this period they should be closely observed.
Fish susceptible to the disease/disorder:
There is a wide range in susceptibility to the disease by aquarium fish of various families and species. Anabantidae, Characinidae, Cyprinodontidae, exotic Cyprinidae appear to be the most susceptible. Poeciliidae, Cichlidae, Centrarchidae (American fresh-water perch) are more resistant to the disease. However, in the Characinidae family, Tetra Von Rio are often affected by Microbacteriosis whereas species in the genus Pristella are not prone to the disease.