i think the idea behind burying fish was leaving the head, tail and bones and to not waste it bury it under the corn. This was probably cooked fish too, so the head and tail wouldnt really rot, and over time the bones would also decompose, just like bonemeal and bloodmeal
if you really wanted i'm sure you could seperate the meat from the bone and dehydrate them and grind them into a powder fertilizer
over a long time the bones would be giving off a slow release of nutrients, mostly nitrogen i think. Land back when the natives were here was much more fertile, i read in a book a cubic foot of healthy soil would have 50+ worms in it, in "teaming with microbes."
bottom line is i think if you did this once a year , that it could be beneficial.
also i've heard yearly applications of eggshells are good