Black Ich  

by Beth

Black ich is an infestation on fish by tiny turbellarian flatworms, genus Paravortex.  While this parasitic problem is largely associated with tangs, particularly yellow tangs, it does infect all fish.  They are easily identified on light, solid colored fish such as the yellow tang, therefore more noticeable on these fish.  They are not, however, an exclusively a tang parasitic problem.

Black ich is not as dangerous to the host fish as are other parasites, such as Cryptocaryon (white ich), brooklynella, and amyloodinium (marine velvet).  Nonetheless, any parasite, particularly in a closed system such as a fish tank, can become a critical life-threatening problem and should be addressed.

These flatworms are introduced in the aquaria by exposure of an infected fish to the fish tank.  Once introduced, it goes through a life cycle which includes infection of the fish itself, attachment and feeding off of the host fish (approximately 1 week), detachment from the fish and release into the aquaria, living in the substrate (approximately 5 days), until an adult worm finds a host fish and attaches to a fish.  The parasite gains its black pigmentation as a result of feeding off of fish tissue.

Unlike white ich that require a host fish for sustenance, this parasite can survive for a long period in the substrate of the aquaria feeding off of detritus.  Therefore irradiation can very difficult.  Making quarantining new fish prior to placing them in to the display tank a much more practical habit then risking infesting your treasured fish tank, especially your reef tank. 

Identification on fish

Small black dots the size of finely ground pepper that will cover the fish.  These spots are the parasite, and may not stay stationary on the fish

Fish will scratch, shimmy, or even convulse a bit because of discomfort and attempting to dislodge the parasites from their body.

If the irritation is bad enough, the fish may start producing excessive slime coating and have a white film appearance.

If the infestation is bad enough, you may note the fish lethargic, breathing heavily, not eating, not swimming well.

Treatment

All infected fish should be put through a formalin bath as detailed at http://forums.saltwaterfish.com/wiki/formalin-bath.

Infected tanks can be left fallow for at least two months, however, in most situations this may be impractical.  If the tank is a strictly fish-only, then it can undergo hyposalinity as detailed at  http://forums.saltwaterfish.com/wiki/hyposalinity .  A light siphoning of the substrate daily for a week may also aid in disrupting the populations of this parasite, however, the hobbyist does not want to disrupt the sandbed to point of creating cycle problems with the aquaria.