Fish eggs from Barred rocks and Rhode Island Reds

[HollowOfWisps]

Fishy tasting eggs in almost every case are caused by the chicken eating something that is “fishy”. Access to a pond or drinking from it, eating water greens, eating fish, consuming small amphibians, being fed spirulina or kelp supplements, feeding a chicken feed with a heavy fish meal base etc.

 

[Perris]

No that's false. It's a genetic defect related to choline processing and the same chemicals that actually make fish taste fishy.

See

Fishy-egg tainting is recessively inherited when brown-shelled layers are fed canola meal​

https://pubmed.ncbi.nlm.nih.gov/19276413/

So the OP's problem may be from too much canola oil in the chickens' diet.