Black Ich

Black Ich (turbellarians)

What You Need To Know:

* Parasitic flatworm infestation; tangs are most often afflicted.
* Primary symptom is small black dots on the fish. (Not to be confused with Clownfish Hyper-Melanization.)
* Best chemical treatments for this disease are Praziquantel and Formalin. Osmotic shock (Hyposalinity, freshwater dips) is an alternative treatment option.

Additional Information

There are two species of turbellarian flatworms which are known to parasitize marine fish: Paravortex sp. and Piscinquilinus subcutaneus. Paravortex are smaller and appear as grains of black spots rather than lumps. Piscinquilinus are relatively large and lie deep within the dermis. As a result, a pigmented dermis may show once killed, resulting in a black spot, regardless of a living parasite within the skin.

Both species are thought to have a single host life cycle producing several juveniles. This cycle is completed in 10 days although from research by Justine et al. (2009) showed the Piscinquilinus remained on the fish for at least 30 days. Investigations also showed poorly developed reproductive organs indicating maturation once the parasite has left the fish. They then produce a ‘cocoon’ like fibrous structure in the substrate, within which they reproduce and therefore re-infect (Justine et al. 2008).

Treatment Options:

  1. Praziquantel – 2 mg/L single dose for 7 days in a QT. Both Prazipro (2.5 mg/L) and API General Cure (2.0 mg/L) contain sufficient concentrations of praziquantel.
  2. Formalin – 45 to 60 minute bath treatment, followed by transfer into a sterile QT afterwards.
  3. Hyposalinity – Treat at 1.009 SG for at least 10 days. This kills both the infective and free living stages of the life cycle.
  4. Freshwater Dip – 5 minute freshwater dip may only provide temporary relief, and not result in complete eradication.