Bacterial Diseases in Fishes
Bacteria are responsible for many fatal diseases in fishes like furunculosis, columnaris, fin and tail rot, vibriosis, dropsy, cotton mouth disease and tuberculosis.
a. Furunculosis Disease:
- Furuculosis disease is caused by Aeromona salmonicida in salmon fishes. It is a non-motile, gram-negative bacterium.
- This disease frequently appears to infect fishes living in the dirty waters containing a large amount of decaying matter.
- The first symptoms of this disease are appearance of boil like lesions.
- Others symptoms are blood-shot fins, blood discharge from the vent, haemorrhages in muscles and other tissues and necrosis of the kidney.
- Bursting of boils allow the spread of this disease among other fishes and also offer suitable areas for fungus growth.
- Fishes severely infected with the bacteria die in good number.
- Remove the severely infected fishes from the pond and supply food containing antibiotics like sulphonamides or nitrofurans.
- Sulfonamides like sulfadiozine or sulfaguanidine are given orally with food at the rate of 22 g / 100 kg of fish / day.
- Other antibiotics like chloromycetin and tetramycin are most effective at a dose of 5-7.5g / 100 kg of fish / day. Disinfect the eggs with 0.015% solution of methiolate or 0.185% acriflavin.
b. Columnaris Disease:
- Columnaris disease is caused by Chondroccus columnaris and Cytophaga columnaris in many freshwater aquarium fish.
- It is a long, thin, flexible, gram-negative slime bacterium (myxobacteriales).
- This disease is often associated with low oxygen level.
- Initially it is marked by appearance of grayish-white or yellowish-white patches on the body.
- The skin lesions change to ulcerations and fins may become frayed.
- Gill filaments are destroyed and eventually lead to the death of the fish.
- Addition of 1 ppm copper sulphate in the pond to control this disease is effective.
- Tetramycin administered orally with food at a rate of 3 g / 100 pounds of fish / day for 10 days is very effective.
- Dip treatment in malachite green (1:15000) for 10-30 seconds and one hour bath in 1 ppm furanase is very effective to control this disease.
c. Fin and Tail RotDisease:
- Fin and Tail Rot disease is caused by Aeromonas salmonicid and A. liquefaciens. However, protozoans and fungi may also be involved.
- It is characterized by appearance of white lines along the margins of fins, the opacity usually progresses towards the base eroding them and causing haemorrhage.
- The fin rays become brittles first and later break leading to the complete destruction of the fins. The infection may also spread on the body surface.
- Fin and tail rot are associated with poor sanitary conditions in fish ponds and with water pollution in nature.
- The Fin and tail rot may be checked at an early stage by keeping fishes in 0.5% copper sulphate solution for 2 minutes.
- Control may be achieved with 10-50 ppm tetramycin and 1-2 ppm of benzalkonium chloride.
- In severe infections the affected parts are surgically removed and the fishes are then kept in 0.04% potassium dichromate.
d. Vibriosis Disease:
- Vibrio bacteria are the causative agents of vibriosis disease in salmon and many other fishes.
- This disease may occur in waters with low oxygen. These bacteria are small gram-negative bacilli, characteristically curved.
- Diseased fishes show large, bright coloured, bloody lesions in the skin and muscles, haemorrhages in eyes, gills may bleed with slight pressure, and inflammation of the intestinal tract.
- Sulfamethazine at a rate of 2 g / 100 pounds of fish / day gives good results. 3 – 4 g / 100 pounds of fish / day for 10 days of tetramycin also give satisfactory results.
e. Dropsy Disease:
- Pseudomonas punctata is the causative agent of this disease. It is characterized by accumulation of yellow coloured fluid inside the body cavity, protruding scales and pronounced exopthalmic conditions. This is known as “Intestinal Dropsy”.
- In case of ulcerative dropsy, ulcers appear on the skin, deformation of back bone takes place and show abnormal jumping. This is a fatal disease in culture systems.
- Removal and destruction of fishes, followed by draining, drying and disinfecting the pond with lime are preventive measures to control the disease.
- The infected fishes may be cured with 5 ppm potassium permanganate for 2 minutes dip bath. Streptomycin and oxytetracyclin give good results.
f. Cotton Mouth Disease:
- The filamentous bacteria, Flexi bacteria are the causative agent of this disease.
- The main symptom is appearance of fungus like tuft around the mouth.
- This can be treated with antibiotics like 10 ppm chloramphenicol for 2-5 days and 0.3 ppm furanace for long term bath.
g. Tuberculosis Disease:
- Mycobacterium is a disease causing agent which is difficult to diagnose without pathological examinations.
- The symptoms are ulcers on body, nodules in internal organs, fin and tail rot, loss of appetite and loss of weight of fish.
- This can be cured with dip treatment in 1:2000 copper sulphate for 1 minute for 3-4 days.
- Antibiotics are not successful. The fishes should be destroyed and potassium permanganate or lime used in the pond.
h. Bacterial Gill Disease:
- This disease is caused by Myxobacteria in salmon fish.
- Many bacteria are found in swollen gill lamellae which show proliferation of the epithelium, and symptoms are lack of appetite.
- This disease is transmitted through water from infected fish. It can be treated with 1-2 ppm timsan or 1 ppm copper sulphate.