I usually take a small can of chipotle peppers in adobo. Take out all the peppers and finely dice one of them (or two if you like your sauce hot). Reserve the other peppers for another use. Then mix the remaining adobo, and your one pepper and mix with sour cream.
I'll post a photo of a walleye taco I did. The walleye I just doctor "Pride of the West Batter" with some cumin, powdered oregano and ancho chili powder, mix with some beer. Fry em. Then some homemade salsa verde, red onion and purple cabbage slaw, pineapple, cilantro and the sauce I mentioned above. My fav fish taco.