Turbellarians (Black Ich)

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

• Dark spots in marine fish may be associated with parasitic turbellarians.

Possible causes and look-alikes

• Pigmentation and other lesions may look similar. Black-spot reports include Paravortex-like and Piscinquilinus worms, rather than the white-spot ciliates.

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 new arrivals, water and spread risk; arrange parasite identification rather than dosing from spot color.

Treatment and correction context

• Off-host stages matter. The available specific research is limited and older, so no universal treatment schedule is presented here.
• Seek an organism- and system-specific plan; do not reuse a freshwater or marine white-spot regimen merely because both are called ich.

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.

• Kent & Olson: Paravortex and Marine Fish Hosts (1986)

  Primary research on parasitic turbellarians and host/system lifecycle.

• Piscinquilinus Black Spot in Naso unicornis

  Specific marine black-spot report; limited scope rather than a general treatment protocol.

• UF/IFAS: Submission of Fish for Diagnostic Evaluation

  Case history and contacting a diagnostic service before collecting samples.