Can someone explain to me why Flowerhorns have a huge growth on their foreheads? I think they look deformed. 
the hump is also reminiscent of some chinese god of wealth or something, so it brings money into the house, which in turn brings bigger tanks and more food. score!
I'm an Asian but unlike most Asians in neighboring Asian countries, I do not believe in superstitions. Yes, arowana, flowerhorns and goldfish apparently bring good luck, wealth and prosperity but I never really believe those stuff at all.
The nuchal hump is also called kok. It's simply a reserve of fatty deposits as Ger correctly stated.