Resource on Growth Inhibitnig Hormones

As I am still toying with the idea of having discus for my planted tank, naturally this topic surfaced as you can't disassociate frequent water changing with discus keeping. Did a bit of snooping around and found a few interesting articles.

Aquarium Stocking Guide

Growth Inhibiting Substance(s) of Fishes

GIS AND GLS

Seems like there is nothing really conclusive and it's not really proven scientifically.