Diaper Rash Remedies:
Desitin diaper cream contains cod liver oil and is often the culprit when diapers smell fishy! Penaten, plain zinc oxide or Balmex works great. Plain zinc oxide doesn't stain or create stinky diapers, and it will wash right out.
If you already have a problem with Desitin damage on your diapers, soak in the diapers in a strong detergent solution for a few days. Then wash with detergent and 1 cup of baking soda. Dry your diapers in the sun for a day or so, and wash them again as you normally would.
and then this:
A Note About Diaper Creams
DON'T use Desitin!! It will make your diapers smell like fish and may cause permanent stains. Vaseline, Aloe Vera jelly, Burt's Bees, plain Zinc Oxide are all good alternatives! To remove the Desitin damage from diapers, wash several times using detergent. You should be able to smell the diapers before they are dried to see if the smell has been successfully removed. Desitin stains may not come out.