Coral Reef Forum

What is Black Spot Disease

Typically a "disease" that is most commonly associated with Tangs and Surgeonfishes, but one that can be contracted by other species as well, what is referred to as Black Spot Disease, Tang Disease or Black Ich is actually caused by an infestation of tiny GenusParavortex member turbellarian flatworms.

Worm Life Cycle

The worms live in the substrate until mature. Then they move to the water column and seek out a host fish. After feeding on the host fish for five to six days, it falls back to the substrate. After an additional five days the worm body ruptures and releases a new population of worms and the cycle continues but in greater numbers.

Symptoms to Look For

Once these worms start feeding on a host fish they acquire pigmentation, which causes the appearance of black spots about the size of a grain of salt on the body and fin membranes. Worms that freely move about on fish, the spots do not always remain stationary. On light colored fish they are easy to see, whereas on dark colored ones they may go unnoticed at first. Fish will scratch up against objects in an attempt to dislodge the parasites, and if allowed to progress the fish become lethargic, loss of appetite and colors occur, rapid respiration develops, and secondary bacterial infections can invade damaged tissue sites.

Treatment

Give all infected fish a freshwater dip followed by a formalin bath and continue treatment in a QT.

Prevention

Reinfection will occur no matter how effectively the fish have been treated if these parasitic tubellarian worms are not eradicated from the display tank aquarium. Unfortunately because they can survive for several months without a host, this is often not an easy thing to do.

Leave the main aquarium devoid of all fish for several months. Siphoning up excess organic matter that can build up on the bottom of the aquarium can help to control their numbers.For fish-only tanks that have no freshwater sensitive invertebrates present, hyposalinity can be applied.