These are open sores on the body surface. Ulcers are typically pink-red in colour, often with a whitish border comprising dead skin tissue.
Some ulcers are shallow (superficial) but severe ones may extend down to the fish's underlying muscle layers and occasionally the internal organs.
The presence of one or more ulcers on fish is a sign of disease and requires prompt action.
Q. Where do ulcers occur on fish?
Typically on the skin. Ulcers may also occur on the fins (notably the fin base) and very occasionally on the eyes or within the mouth cavity.
Q. Can any type of fish get ulcers?
Yes. Pond fish, coldwater and tropical aquarium fish, and marines are all susceptible.
Q. What causes ulcers?
There are several possible causes but usually a bacterial infection is to blame. These ulcer-forming bacteria may naturally be present in the aquarium or pond but generally they will only cause problems under certain adverse conditions. Skin injuries (e.g. caused by net damage) or damage caused by various types of skin parasites can also -lead to skin ulcers. Unfortunately, the ulcer's appearance gives few clues as to its underlying cause.
Examples of bacteria that cause ulcers:
1) Aeromonas, Pseudomonas and Vibrio.
These are common causes of ulcers in aquarium and pond fish.
Several species and strains of these bacteria have been implicated.
For example, an ulcerative disease of Goldfish and Koi ('Summer Ulcer Disease') is caused by Aeromonas salmonicida subspecies achromogenes.
2) Flavobacterium (formerly known as Flexibacter).
This ulcer-causing bacterium is also responsible for the condition known as 'mouth fungus' ( Columnaris Disease).
3) Mycobacterium species.
These bacteria are responsible for a chronic wasting disease in fish known as 'fish tuberculosis' (fish TB). In addition to skin ulcers, symptoms of mycobacteriosis may include: pop-eye, body wasting, stringy faeces, colour fading and, in some cases, bent spines. Mycobacteria invade the fish's internal organs, making the disease difficult to treat using commercial anti-bacterial remedies from the aquarium store. By the time outward symptoms are noticed the internal organs may already be badly diseased, and the fish's chances of survival are slim.
Antibiotics generally offer the best chance of a cure -but only a minority of cases successfully respond to treatment.
Q. Can viruses cause ulcers?
Yes, a few can. Unfortunately, viral infections of fish are often hard to diagnose and cannot be treated using aquarium disease remedies or antibiotics.
If a virus is suspected then isolate the affected fish and provide them with optimum water conditions and good food: this may help the fish's immune system to fight off the virus.
Q. Is it true that unhygienic aquarium or pond conditions can lead to ulcers?
Most certainly yes! Outbreaks of ulcers in fish can often be traced to dirty water conditions. Proper filtration, avoidance of overcrowding, and regular aquarium maintenance (eg routine part water changes and siphoning excess dirt from the gravel) will greatly reduce the likelihood of ulcer outbreaks.
Q. What causes small ulcers around the head and lateral line of cichlid fish?
This is often due to a disease condition known as 'Hole-in-the-Head' (HIH).
It affects mostly South American cichlids such as Discus and Oscars.
This disease syndrome has not been extensively researched, however it seems that certain species of flagellate protozoan parasites (Hexamita and Spironucleus) are involved, at least in some cases. Poor nutrition and/or bacterial infections have also been implicated.
Successful treatment has been achieved using metronidazole and/or antibiotics, both available from the vet.
Q. Are skin ulcers vulnerable to fungus infection?
Yes. The ulcerated area of skin is prone to infection by aquatic fungi ('water moulds'). Saprolegnia fungus is often to blame and manifests as white-grey cotton wool-like growths. In such cases treat the fish with anti-ulcer and anti-fungus remedies. A good combination of remedies would be Melafix (for dealing with the ulcer) in conjunction with Pimafix (for tackling the fungus).
These two herbal-based treatments (manufactured by Aquarium Pharmaceuticals Inc.) can be used simultaneously.
Q. Is it true that large ulcers can upset the fish's water balance?
Yes. Fish have to maintain a constant level of salts within their bodies and this is achieved by an energyconsuming process known as osmoregulation.
Extensive ulcers can upset osmoregulation by breaching the skin's water-proof layers, thereby making the fish 'leaky' to salts and water. As a result, the fish's osmoregulatory system has to work much harder to compensate for these leaks.
In severe cases where the ulcer(s) cover a large surface area of skin the fish's osmoregulatory system may be unable to cope, with life-threatening consequences.
Q. How are ulcers treated?
Many ulcers are treatable using conventional anti-bacteria or anti-ulcer remedies that are sold for aquarium and pond use. Herbal-based remedies (such as Melafix) are now available for fish and these are proving very popular for treating ulcers and other bacterial skin conditions. Some of these proprietary treatments also speed up tissue healing, thereby reducing the likelihood of secondary fungus infections.
In the case of severe or recurrent ulcers (including those accompanied by Pop-Eye or Dropsy), these may require antibiotic treatment from the vet.
Q. Does salt help in dealing with ulcers?
In the case of freshwater fish, salt (pure Sodium Chloride) will help alleviate osmoregulatory stress caused by extensive ulceration. Salt will also help reduce the likelihood of fungus infections.
However, before adding salt to an aquarium ensure that ALL the fish to be treated are salt-tolerant. If in doubt seek advice.
For those fish that are salt-tolerant, add between 2 to 5 grams of salt per litre, as a long-term bath (e.g. several days). At the end of treatment the salt is removed from the system by performing one or more water changes.
Many anti-ulcer remedies can be used in conjunction with salt, but always check the manufacturer's instructions.
Q. Can ulcers cause scarring to the fish's skin?
Sometimes the healing ulcer will turn very dark. This is due to a localised accumulation of melanin pigment which is produced by the fish as an immune response to the ulcer. Skin melanisation is not harmful but can appear unsightly and may take a long while to fade.
Q. How long do ulcers take to heal?
Assuming any underlying infection has been successfully treated then the damaged tissue will generally heal in about 2 to 8 weeks. The rate of healing will be influenced by many factors, notably water temperature. For example, in pond fish an ulcer will heal much faster in summer than in winter.
Q. What is meant by 'debriding' an ulcer?
This is sometimes performed on severe ulcers, particularly on large pond fish such as Koi. It involves the gentle removal of any dirt and dead (necrotic) tissue within the ulcer, plus any loose scales. This is done using forceps (tweezers) and cotton-wool swabs. The aim is to clean up the wound.
A povidine-iodine solution (as sold for fish use) may be used to disinfect the cleaned ulcer which can then be sealed with a waterproof paste (e.g. Orabase). This delicate procedure requires skill and the fish may need to be anaesthetised beforehand to minimise stress.
For further information about fish and fish keeping, visit us at www.aquarian.com
Last updated March 2005