Oscar with hole in the head disease
This disease normally only affects cichlids. It is caused by a protozoa called Spironucleus vortens which normally lives harmlessly in a fishes gut.
If the fish becomes stressed the immune system can be compromised and the Spironucleus vortens protozoa is then able to increase in numbers and spread through the fish's blood stream.
When the parasite is in high numbers due to the immune system being compromised it is able to spread from the gut and get in to the blood of the fish where it can infect other areas of the fish. The protozoa damages the fish's gut wall in doing this and in turn it affects the fish's ability to digest food. Affected fish often lose condition and pass jelly like faeces.
The characteristic symptom of the disease is small holes in the the head and lateral line of a fish which usually start at the sensory pores of the fish. It is thought that the parasite blocks the blood vessels to these areas causing tissue death and ulcers. Spironucleus vortens can also be found at these sites.
This disease is often confused with hexamita which is a different but very similar disease but with different symptoms.
All cichlids are at risk of catching this disease and discus seem to be most at risk closely followed by oscars. There are several symptoms but an infected fish may not show all of the possible symptoms.
Metronidazole is the best treatment. The recommended dose is :
A quarter of a teaspoon per 75 litres.
Treat every 24 hours with a 25% water change made before each treatment.
An alternative method is to add the Metronidazole to the food. Use frozen food which should be thawed out and then add two teaspoons of Metronidazole powder to 1 pound (0.5 kg) of food, mix it thoroughly and then re freeze. The food should be used on ten consecutive days.
Don't expect to see the ulcers all healed up. The ulcers are just a symptom of the disease and they will take time to heal once the Spironucleus vortens protozoa has been killed off. Healing should start within a few days of the treatment.
This disease mostly affects fish which are stressed due to over crowding, poor conditions including poor water chemistry or poor water quality. If these causing factors are not dealt with then the fish won't respond to the medication quite as well as they might and there is every chance that the disease will return.
With deep open wounds secondary infections pose a greater risk then normal. If the wounds become infected it will prevent healing so until healing has begun keep a very close eye on the wounds. There is no need to treat the fish if no infection is present.