Yellow grubs

[Minnetonka]

I am a former MN DNR fisheries biologist. The people who said that the photo was of the Yellow grub were right on. Clinostomomum Marginatum is the latin name. The Yellow grub is a larvel form of one of the flukes or flatworms (trematoda). This worm appears as a yellowish swelling in or just under the skin of fish such as Rock Bass and Perch. The adult worm lives in the mouth of the great Blue Heron and other fish eating birds. The eggs pass in to the water and hatch into free swimming larvae (mirracidia) which enters snails. Inside snails these larve reproduce and eventually leave as tiny free swimming forms called (cercaria); the cercaria burrow into the skin of a fish and become encysted there, remaining until the fish is eaten by a bird. In the bird the parisite complete thier development and become adult worms. They are harmless to man and do little damage to fish. The are practlly impossible to eradicate because it would be necessary to destroy all fish-eating birds or all snail host. Fish from shallow weedy water tend to have more grups do the the proximity to more snails. Deep water fish tend to be "cleaner".