Bacterial Diseases

A number of bacteria are known to infect fish causing conditions such as fin and tail rot, ulcer disease and furunculosis, and gill infections. Among these are Myxobacteria (slime bacteria), and bacteria in the genera Pseudomonas, Aeromonas, and Hemophilus among others. The hobbyist usually finds it difficult to tell these infections apart and cannot isolate and identify the causative organism. The therapy of the infection is similar however so the differences are not too important for practical purposes. Myxobacteria are responsible for an infection in the mouths of fishes which has been misnamed "Mouth fungus" and also cause a condition called Columnaris disease which is due to an infection by a bacterium, Cytophaga columnaris.

The features which most bacterial infections have in common are ulcers (open sores) on the skin, fins and mouth, internal abscesses, and increase mucus on the skin and gills. These skin ulcers are like the top of an iceberg in that they give only a clue to the marked infection inside the body of the fish. Local treatment with ointments or with dyes such as malachite green or methylene blue in the water is completely useless for curing the infected fish but may help to prevent transmission of the disease. Pop-eye and dropsy can also be caused by advanced bacterial infections.

Considering the number of bacteria which can infect humans, it would be surprising indeed if only these few recognized groups are the sole cause of fish bacterial infections. Other bacteria in the author's personal experience falling into none of the above described categories can also cause disease. These may be less pathogenic but attack fish in a generally weakened condition. Bacteria such as these are known as opportunists. Aquarium fish will also be adversely affected and weakened by cloudy water which generally contains vast numbers of usually harmless bacteria.

The treatment for bacterial infections requires the use of antibiotic in the aquarium water which will be absorbed by the fish and which will reach the internal areas of infection. The tetracycline antibiotics are generally effective and are sold under various trade names. The forms of the drugs intended for human consumption can sometimes be used in aquarium water. Do not use any oral liquids or suspensions which may contain flavoring and sugar. This may result in giving rise to bacterial infestations in the water worse than the disease being treated. The best form to use is a capsule of pure drug which can be emptied into the aquarium water. Some forms of these drugs will yellow the water and cause the formation of scum and foam on the surface. Penicillin in its usual forms is effective against only a limited number of bacteria. A newer form of Penicillin, Ampicillin, has a much wider range of effectiveness and has been used by many people with considerable success. This drug is non-toxic to fish in high concentrations and is colorless. The recommended dose is 50 mg. per gallon of water for both the Tetracyclines and Ampicillin.