Pathogenic bacteria in the pond are responsible for a multitude of common fish ailments. These bacteria are almost always present in the pond, but healthy, unstressed fish with high immunity levels will not usually become infected. As with many pond fish ailments, if the fish are unhappy, the cause of stress should be determined and dealt with before any resulting bacterial infection can be properly treated.

External Bacterial InfectionsBacterial infections can affect one, or multiple fish in the pond. If one fish has been infected it may be that the fish had a physical injury which has become infected. If more than one fish is suffering, the indication is that the pond’s maintenance may need improving. A partial water change should be carried out to dilute any possible pathogens, and the whole pond should be treated with an anti bacterial remedy.Fin Rot and Mouth Rot – Fin rot can affect any of the fish’s fins or tail. It is visible as a reddening, and sometimes rotting away of the thin membrane between the bony rays.Mouth rot can affect the fish’s upper or lower mouth and, like fin rot, tissue around the mouth looks red and angry and begins to erode. Other symptoms would normally include those associated with stress.

Ulcerations – Ulcers are similar in appearance to rot; red angry looking tissue, and deep sore lesions. Ulcers present on the tougher body tissue of the fish, rather than the more delicate mouth and fins, usually indicate a more advanced bacterial infection.Fish with multiple or large ulcerations may need to be separated from the pond and treated in a quarantine tank. Ulcers are sometimes present if the fish has an internal bacterial infection which has spread to the fish’s extremities. Anti ulcer treatments are usually more potent than anti bacterial treatments and can be used to treat internal bacteria.

If treated properly, and the underlying causes of external bacterial infections are dealt with adequately, the fish will re-grow most fin and mouth parts, and ulcers will heal, although they may possibly leave some visible scar tissue.

Internal Bacterial InfectionsInternal bacterial infections are usually more advanced than external as the symptoms are harder to spot and can take longer to manifest. Indications of internal bacterial infections are;Pop Eye – Pop eye can affect one or both of the fish’s eyes and, as the symptom describes, the eyes appear to bulge out from the fish’s head.

Abnormal Swimming/Balance – If the fish seems to swim or rest at peculiar angles, this could be an indication that the swim bladder has become infected by a bacterial infection. The swim bladder function can also become impaired during spells of cold weather, it is usually safe to rule out bacterial infection during the winter, unless there are other supporting symptoms of internal infections.

Abdominal Bloating – if the fish’s belly has bloated and other symptoms of internal bacterial infection are visible, then this is usually a further indication of bacterial infection. Abdominal bloating can be caused by a number of ailments. Bloating should only be treated as an internal bacterial infection if there are defiantly other supporting symptoms.Dropsy – Dropsy is a collection of symptoms which indicate that the fish is suffering with an advanced internal bacterial infection. The main visible indication that a fish has dropsy is that the scales begin to stick out, which gives the fish’s body a pinecone like appearance. Other symptoms include abdominal bloating and pop eye.

Although treatable in some cases, dropsy frequently results in fatalities. Dropsy normally only infects a single fish, but the pond should be given a partial water change and treated with an internal bacterial remedy.