The Stream Doctor

April 21st, 2003

Email YOUR Questions directly to the Stream Doctor. This is your opportunity to get an experts professional opinion on anything stream related.

Q. From John in Newfoundland: Hello: Last year I caught a number of wild trout that had some kind of disease on their skin. At first glance, it looked like they had been dusted with salt and pepper - raised dots about the size of salt crystals. I searched the internet and it looks like they have a disease called "white spot," but this disease is referenced to stocked fish ponds and these are wild fish from rivers that run into the Atlantic Ocean.

My questions are: How dangerous is this disease for our wild stocks? And is there any danger of eating fish with this disease? I caught browns and brookies with it.

A. Fish diseases and pathology are not my area of expertise, so for the answer to your questions, I called Vicki Milano, a pathologist with the Colorado Division of Wildlife. She provided me with the following information.

First, the answers to your questions. Although both diseases ("Black spot" and "Whitespot" or "Ich") are common in the wild, it would take unusual conditions of severe crowding and high water temperatures to threaten wild stocks. Severe infections can kill fish and "Ich" may be the most important fish parasite in the world, especially when it infests fish cultural facilities. Neither parasite can infect humans and cooking kills the parasites.

Black spot (Apophallus brevis)is a trematode parasite found in brook and brown trout and appears as sand grain-sized spots on their skin. For further information on the parasite's life-cycle, photos, and other information, go to:

Whitespot or Ich (Ichthyophthirius multifillis) is a protozoan parasite that shows as small, white nodules on the skin, much as you described. It is highly contagious and widespread among freshwater fishes in the temperate zones of the world. For more information on its life cycle and other characteristics, go to:

These are one-page websites furnished by the State of Maine's Fish Health Laboratory.
~ C. E. (Bert) Cushing, aka Streamdoctor
105 W. Cherokee Dr.
Estes Park, CO 80517
Phone: 970-577-1584

The 'Stream Doctor' is a retired professional stream ecologist and author, now living in the West and spending way too much time fly-fishing. You are invited to submit questions relating to anything stream related directly to him for use in this Q & A Feature at

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