Aquarium Disease Hexamita Glossary Guide: Hole In Head Parasite
The pinhole pits that appear above a discus’s eyes are rarely the parasite itself — they are the late-stage signature of a months-long internal infection that started in the gut. The disease known as aquarium hexamita explained in older literature is a flagellate protozoan that lives in the intestine and only erupts externally when stress and malnutrition crack the fish’s defences. This glossary entry from Gensou Aquascaping at 5 Everton Park covers the parasite’s biology, the connection to aquarium hexamita explained and hole-in-head disease, and effective metronidazole protocols.
Definition in 50 Words
Hexamita refers to small intestinal flagellate protozoans, primarily Hexamita salmonis and the closely related Spironucleus vortens, that infect cichlids, gouramis and discus. They live in the gut at low levels in healthy fish but proliferate during stress, causing weight loss, white stringy faeces, and the pitted lesions known as hole-in-head disease.
The Parasite Biology
Hexamita is a tiny eight-flagellated protozoan around 7-12 micrometres long. It anchors to the intestinal lining, multiplies by binary fission and forms cysts that pass out in faeces, infecting tankmates through the water column. Spironucleus vortens is now considered the more common pathogen in cichlids — older literature lumped both under “Hexamita” and the colloquial name has stuck.
Hole In Head Disease (HITH)
The classic external signature is small (1-3 mm) pits along the lateral line and forehead, sometimes with white mucus extruding from each pit. Affected discus and oscars often have parallel symptoms — emaciation despite feeding, white stringy faeces, darkened colouration and reluctance to eat. Heavy ich-style spotting is absent; the lesions are deeper and inflammation-driven.
Triggers for Outbreak
Low-grade hexamita lives in many cichlids without causing disease. Outbreaks correlate with chronic stress from poor water quality, overcrowding, inadequate diet, and unstable parameters. High nitrate (above 40 ppm) is a particular trigger in discus tanks. Replacing carbon-filtered water from the water care range on a strict 30 per cent weekly schedule reduces background stress sharply.
Diagnosis
Stringy white faeces in a cichlid showing weight loss is presumptive evidence. Confirmation requires microscopic examination of fresh faecal smear under 400x — the flagellates are visible swimming, looking like small grain-of-rice shapes with a darting motion. Positive smears combined with HITH lesions seal the diagnosis. Bacterial co-infection is common and often needs separate antibiotic treatment.
Metronidazole Treatment Protocol
Metronidazole is the gold standard. Dose 250 mg per 40 litres in the tank water three times over 72 hours, with a 50 per cent water change before each redose. Pre-soak food in metronidazole solution at 1 per cent w/w for systemic gut treatment when fish are still feeding — Discus Hans and Seachem MetroPlex protocols are widely followed locally. Repeat full course at day 10 to catch newly hatched cysts.
Praziquantel for Coinfection
Praziquantel does not kill hexamita but is often used alongside in HITH cases because intestinal flukes worsen the gut damage. Dose 2 mg/L in the display tank, repeat at day 7. Many keepers run praziquantel during quarantine on every new arrival from busy local shops to clear baseline parasite loads.
Diet During Recovery
Cichlids with active hexamita lose appetite. Tempt with high-quality frozen bloodworm, fortified flake, or the cichlid food range — small frequent feeds work better than one large meal. Once eating, rotate in vitamin and immune-boost soaks to rebuild reserves. Avoid feeding live tubifex or earthworms during outbreak because they may reintroduce flagellates.
Tank Hygiene Post-Treatment
After the second metronidazole course, do a deep vacuum of the substrate and replace mechanical floss in the canister filter to remove cyst reservoirs. Bleach nets and siphons in 1:30 sodium hypochlorite for 10 minutes, then dechlorinate. Move surviving fish through the quarantine tank range for 14 days before reintroducing.
Singapore Discus Considerations
Local discus from Iwarna and Qian Hu often arrive parasite-loaded due to high stocking densities at breeding farms. A prophylactic metronidazole and praziquantel quarantine for every new discus prevents months of chronic illness. Bare-bottom quarantine tanks at 30°C with daily 50 per cent water changes accelerate clearance compared to planted display setups. Tropical ambient temperatures actually help — warmth speeds parasite metabolism, raising drug uptake and shortening the cycle.
Connected Terms
Hexamita interacts directly with stress response (cortisol elevation triggers outbreaks), gut anatomy (the parasite lives in the intestine), and water quality. Treating hexamita without addressing the upstream nitrate spike that triggered it guarantees recurrence within months.
Related Reading
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