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.
 
https://www.researchgate.net/publication/282610017_Evaluation_of_formula...