What is the yummy looking yellow sauce in the photo? Also, how much fish are you using with this quantity of marintate

You'll have to wait for the recipe author to respond about the yellow sauce question.

The recipe says that it serves 6 so logically the marinade (which is nearly 3 liquid cups based on the ingredient list) is enough for six pieces of fish as pictured in the photo. That works out to 1/2 cup of marinade per fish fillet/steak which makes sense.