the Native Americans I sometimes camp with taught me this method of cooking fish on a campfire.
Gut and gill the fish, leave the scales on. Stuff the fish with herbs and spices or veggies.
Cover entire fish with river bank clay about ½” thick. place fish in the firepit and cover with coals. Let it cook until the clay is dry about an 60–90 minutes. the scales should come off with the clay when you split the pot and serve.