Antibiotics are chemical substances produced by microorganisms that either
destroy (bactericidal) or inhibit the growth of other microorganisms (bacteriostatic).
Antibiotics are classified into:
- Broad spectrum, which means that they are active against a wide
range of microorganisms – both good and bad.
- Narrow spectrum drugs target a specific group
of microorganisms and are able to interfere with a metabolic process specific to those organisms.
However, the microorganisms under attack don’t take all this sitting down. Many are able
to produce enzymes that neutralise antimicrobial compounds. Others can acquire resistance
to weak, short-term or repeated exposure to antibiotics.
Some of the Antibiotics available are:
- Broad Spectrum Penicillins: Includes Amoxycillin and Ampicillin
- Chloramphenicol is a broad spectrum antibiotic.
- Gentamicin is a broad spectrum antibiotic.
- Nitrofurans are synthetic antimicrobials and are effective against many fish pathogens. These
are well absorbed through skins and ideal for bath treatment. However these are carcinogenic and
could be a potential hazard.
- Oxytetracycline is a broad spectrum antibiotic. If used for bath treatments it chelates with
calcium and magnesium ions in the water and effectiveness is reduced very much. The degraded form
can be toxic to humans and fish.
- Quinolones are narrow spectrum drugs, acting mainly against Pseudomonas and Aeromonas. Again
these chelate in hardwater and not so effective for bath treatments. They are well absorbed
through medicated food.
At best antibiotic treatment should be the last course of action, when everything else is
ruled out or cannot work. Dumping antibiotic in tanks at will should be strictly avoided.
Methods of use:
- Bath Treatment: Not many are suitable or effective for bath treatment. Usually the drug
chelates with calcium and magnesium ions in the water significantly reducing the effectiveness.
- Injections: Highly effective, but may not be suitable mode of administration for small
tropicals and also for many infected fish. Can be considered for expensive fishes such as
Arowanas. Only skilled veterinarians can do this treatment.
- Medicated food: This is an option that is easy to handle and reduces stress to the fish.
Also many affected fish can be treated at once. One disadvantage is it not possible to ensure
all fishes get the necessary dosage and also some may not be in a position to eat. Top dressing
of standard food with antibiotic is possible but the risk is palatability and washing away of
medicine in water before it is eaten.
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