I have noticed something of great concern in fish that I have caught in Eastern Ontario over the years particularly the Pembroke and surrounding area. Embedded in their flesh a several 14 inch white parasitic worms. I have my suspicions as to their origin…cattle farms in this region. These worms I have heard are in the intestines of cattle to aid in digestion. When the eggs from these worms are excreted in manure and washed into the water system after ever rain they infest a new host fish. Subsequently they end up killing the fish. Have you heard of this phenomenon If so what can be done about this so called invasive species

Posted on December 13th, 2014

Hi Calvin…Actually, you have nothing to be concerned about. All fish have parasites. I will try and give you some technical info. so that you are aware of some of the types of parasites that are commonly found in our freshwater fish. There are several “symbiotic” parasites that are common in many of our warm-water fish. One of the most common is the tapeworm (Cestodes). The tapeworms for example we find commonly in walleye and bass are the adult stage of the parasite. The parasites are passed on from fish to fish when their eggs are excreted, and than eaten by a family of plankton knows as “copepods”. When they are eaten by the copepods the eggs develop into a larvae. The copepod must then be eaten by larger fish for the parasites life cycle to continue. When a small fish eats the infected copepod, the tapeworm larvae normally embeds itself either in the muscle tissue or internal organs. The small fish than has to be eaten by a larger fish such as a walleye or bass to complete the tapeworms life cycle. When the larger fish ingests the smaller fish with the larvae, the larvae lives in the intestinal tract of the larger fish where it completes it’s life cycle and than starts again. It’s common if larger fish that are kept for eating die, and are kept in a plastic bag or cooler, to see the tapeworms that have come out of it’s host. It is safe to eat fish that have these parasites as long as you properly cook the fish. Freshwater fish should never be eaten raw as “sushi”. Here are a list of other common parasites that you can detect in certain freshwater fish:

Black Spot – Small round spots under skin or in flesh. Caused by larval flukes that develop in fish and are eaten by birds to continue life cycle.

Dermal Sarcoma – Infects walleye, appear as “warts” on surface of skin.

Yellow & White Grub- Fluke that looks like a yellow spot (tiny ball the size of a kernel of rice), usually in the flesh. Caused by a larval fluke. Birds needed to continue life cycle.

All freshwater fish that have the above parasites are fine to eat, in some cases you can remove the cysts from the flesh when you are cleaning them. The important thing is to cook the fish properly….God bless you, Italo

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