Description

Symptoms: the first symptom is slimy, white mucous feces, even while still eating and acting normal. Further signs are the fish hiding in the corner with its head down, the head above the eyes gets thin, they blacken in color, and swim backwards. As it is a disease of the digestive tract, a wasting away or loss of appetite may be experienced.

Hexamita, Spironucleus and Protoopalina are intestinal flagellated protozoa that attack the lower intestine. Discus and other large cichlids, especially Oscars, are especially prone to Hexamita.

Under certain conditions, which can not yet be specified clearly, the flagellates living in the fish's intestines start reproducing in huge numbers. This results in serious food competition for minerals with the fish, which then suffers from mineral deficiency. As a reaction to the mineral deficiency, it starts breaking down bone tissue in order to gain access to minerals. Since the fish has the greatest amount of bone substance in its head, massive breakdown occurs in this region which becomes visible in the form of holes. In the meantime, the flagellates migrate to the closest body surface. Since the holes that have formed represent the closest body surface, they can be found at the base of these holes. Accordingly, the flagellate alone used to be considered responsible for this disease. In fact, though, the combination of the mineral deficiency with the massive reproduction of the flagellates produces the holes. Tapeworms, threadworms and fish tuberculosis, as well as malnourishment, can cause the formation of holes. Occurrence of the hole-in-head disease has only been observed in very soft water until now.

Caution: Hexamita and Spironucleus are normally found in small numbers in the intestines of fish as harmless co-habitants. It isn't until the fish are weakened by other factors, e.g. inappropriate fishkeeping, deficiency symptoms, etc., that the flagellates spread and cause the fish to die.

This disease is often confused with another disease called Head and Lateral Line Erosion (HLLE), which used to be called "hole-in-the-head" disease, because both these diseases are often seen simultaneously in the same fish. Head and Lateral Line Erosion disease looks like cavities or pits on the head and face. This is not a protozoan disease, but is actually caused by environmental conditions.

Treatment

Remove any activated carbon from the filter for the duration of use. Switch off any UV-C appliances and CO₂ fertilizing appliances. Please also ensure that skimmers and ozonisers in saltwater are switched off. Change 50 % of the water prior to application of medication. Aerate the aquarium using a diaphragm pump with airstone during the treatment. During the treatment continue feeding the fish sparingly, provided that they don’t refuse the food intake. We recommend cleaning the filter prior to use of medication.

An effective treatment is the drug metronidazole. Metronidazole is an antibiotic for anaerobic bacteria with anti-protozoal properties. This drug is reef safe, and medications are either added to the water or mixed with the fish food. Metronidazole works by ceasing the growth of bacteria and protozoa. A combined treatment in the food (1% in any food the fish will eat) and in the water (12 mg per liter) is recommended. Repeat the water treatment every other day for three treatments.

After the treatment

After the treatment, please filter the aquarium water for 24 hours using activated carbon to remove the residues of medication. Afterwards the activated carbon should be duly discarded. The addition of a bacterial starter to the aquarium water helps to replace any purifying bacteria which may have been affected.