these sound like yellow fat worms. a real problem in pickeral and yellow perch, i don't often see them in trout. it seems to be related to water temperature: warm = wormy!
then, it's numbers are also affected by shallow water: deep = good!
they are not a problem in cooked fish, the worms are called "fat" worms because they cook out and become just fat (you know, like the gross worms people eat in the jungle...?!) they often show right through the skin around the head.
if there is only a few, i pick them out. if it's full of them, it's garbage. if i'm filletting the fish, after i take the skin off, i "candle" the clean fillette. to do this, it's just like your grand mothers used to do for eggs (to see if the roster got to it first and fertized it!) - hold it up to a strong light. these parasites are clearly visible by doing this, although you need to check both sides (you also catch any scales that got on the meat). if you see any just use a knife to cut down to the worm, then use the tip to pull out the whole worm.
a nasty parasite, still, i prefer them to "bird shot" parasites - they are hard on the teeth!!!
ps; if you see some bird shot parasites in the flesh ( bird shot or smaller black/dark brown round hard shells) there are a lot more you can't see. again they are fine if you full cook your fish...but i will not eat it - to crunchy!!!