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Self-Improvement & Hobbies

Bacterial diseases

How do you know when your fish has a bacterial infection and what to do about it
CATS Classified In The Straits Times - September 11, 2010
By: Wong Wei Chen
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Bacterial diseases

Last week, I talked about symptoms of illness in fish, and how you can learn to recognise them. Not that I’m hoping for your fish to fall sick, but assuming that they have been afflicted, what you need to do is to quickly identify the nature of the affliction and how you can treat the patient.

Types of ailments
Diseases that affect fish are generally one of the following types:

    Bacterial diseases

    Parasitic diseases

    Fungal diseases

    Physical ailments

Among these four types of maladies, diseases of bacterial or parasitic origin tend to be more common. This week, we’ll focus on illness caused by bacterial infection.

When bacteria become harmful
Most bacteria responsible for illness in fish are actually normal inhabitants of aquatic systems, and usually do not pose a problem. However, when fish become stressed by environmental factors such as drastic temperature changes, poor water quality or rough handling, their immune systems will be weakened, and they will become more vulnerable to bacterial infections. Furthermore, some of these stress factors – such as dirty water – may promote bacterial growth, which in turn increases the likelihood of an outbreak.

So while you administer treatment, make sure you tackle the root causes as well. If necessary, install a heater or relocate your aquarium to a cooler place to keep the water temperature within the optimal range. Conduct ammonia and nitrite tests to check the water chemistry. You may also want to bring your nose close to the water and inhale – if you don’t like what you smell, chances are that your fish aren’t having a good time either.

Symptoms & treatment
A fish afflicted by bacterial infection often displays symptoms like red streaks or spots on the fins or body. These may escalate into tail and fin rot if left untreated. Swelling may also occur at the abdomen or eyes, or scales may protrude. Bacterial diseases are best treated by antibiotics such as erythromycin or the penicillin family of antibiotics (for example, penicillin, amoxicillin and ampicillin). Alternatively, opt for versatile, broad-spectrum antibiotics such as tetracyclines, which target many types of bacteria (thus the epithet “broad-spectrum”).

Treatment methods
You can treat sick fish either through a bath treatment or mixing antibiotics with their food. A third, and very effective method, is an injection, which sends the medicine right into the fish’s blood stream. But I can’t imagine poking a needle into my fish, and I think most hobbyists would baulk at the idea too, so let’s concentrate on the first two methods.

Bath treatment
This is when you simply put antibiotics into the water. This method is the easiest, but comes with disadvantages. First, there is the possibility of under-dosing, which makes the treatment ineffective. On the other hand, over-dosing increases the likelihood of the bacteria developing resistance to the antibiotic. 

When only a few fish are afflicted, put them in a quarantine tank to administer treatment. Administer medication to the main tank only if most of your fish are unwell.

Mixing with food
This method is more targeted and can be more effective than the bath treatment. But it presupposes that your fish are still eating – meaning that they are not so sick that they’ve lost interest in food. Make sure you spot illness early so that you can employ this method effectively.

There is a possibility that antibiotics which kill pathogenic bacteria may also kill the nitrifying bacteria in your substrate. So while you’re administering medication, make sure you regularly monitor ammonia and nitrite levels, and when necessary, apply an ammonia-removing reagent to the water.



Sick fish