Hole in the Head (HITH)

When to act urgently

Breathing distress, rapid deterioration, inability to remain upright, major wounds or multiple deaths require urgent aquatic-veterinary or fish-health help. Check aeration and water immediately; do not wait to match a photograph.

What you may notice

• Pits or erosion around the head and lateral line; lesions may worsen or ulcerate.

Possible causes and look-alikes

• Similar lesions can arise with different underlying problems. Appearance does not establish Hexamita or one universal cause.

Check first

• Record species, aquarium type, recent arrivals or changes, appetite, breathing, and how many fish are affected. Check aggression, injuries, filtration and aeration.
• Test ammonia, nitrite, pH and temperature; measure dissolved oxygen where possible and salinity in marine/brackish systems. Correct verified environmental problems using suitably prepared water, avoiding abrupt chemistry changes.
• Review water trends, nutrition and social stress; record lesion progression and other signs.

Treatment and correction context

• Worsening or ulcerated lesions need examination for secondary infection and other causes.
• An antiparasitic is not an automatic first step. Correct documented husbandry problems while arranging assessment; do not infer a single cause from nitrate alone.

Record for your next step

Write down onset and progression, species, affected/total fish, recent introductions, feeding observations, dated water results with kit units, and every action or product already used. Contact the diagnostic service before collecting or shipping samples.

Sources and scope

Source checks: 2026-10-03. Educational editorial summary; no independent veterinary review.

• Fish Vet: Hole in the Head Disease

  Specialist veterinary discussion of head/lateral-line lesions and contributing husbandry factors.

• UF/IFAS: Submission of Fish for Diagnostic Evaluation

  Case history and contacting a diagnostic service before collecting samples.