Dead fish = plant food?

Assuming a planted tank with a low bioload, would leaving a dead fish
in there be all that bad? wouldn't the plants use the decomposing fish
as fertilizer?
I noticed a dead oto in my tank yesterday. I didn't fish it out right
away, but returned about 3 hours later to remove it but it was gone. I
assume the currents must have taken it into a more densly planted
section of the tank.
Thoughts?