Hi beef , Ive got a few cod myself with those red things , I thought they may have been an external parasite different from the typical red cod worm but I didnt really pay much attention as I only keep red cod for bait. Must have a closer inspection next time.
The half doz cod I got during the week had no external parasites and were in fairly good condition but when I took them out of the bin there was a dozen or so skinny wee worms squirming around in the half inch of rain water still in the bin. The cod wouldn’t of looked so appetizing then if I had planned on eating them but I have never heard of anyone getting crook from them.
I keep the cod for shark baits during the summer. in fact red cod is the only bait I use if targeting Sevengills and Tope and it works well.
For sharks I use either 100lb wire trace , 100lb sure-weld and a 10/0+ circle hook with big slab of red cod fillet.
So dont throw away all the sick looking cod lol