Here is a research brief on protein/feed formulations that underwent study. There is both a brief and you can read the entire 91 page reseach.
Similarities of koi nutrition with carp nutrition are advantageous owing to the availability of adequate
information based on which diets can be formulated and evaluated. However, it is to be remembered that
commercially available diets are not always formulated and evaluated using such information, leading to the
availability of diets, worldwide without any specified standards.