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April 21st, 2003
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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:
www.state.me.us/ifw/fishing/fishlab/vol2issue8.htm
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:
www.state.me.us/ifw.fishing/fishlab/vol3issue4.htm
These are one-page websites furnished by the State of Maine's Fish Health
Laboratory.
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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
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