I'm willing to bet that the hump is related to species breeding. My large wild Mono hard a hump once he got bigger and the smaller male started to get a hump too, yet he is a smaller size then the larger male. This would lead me to believe that the smaller male's hump is a reverse dominance reaction to the larger ones.
Also my female has been looking like she will lay eggs for the last week so two days ago I put a large flat rock in with them to see what would happen.
Today the female is biting the rock, messing with the sand around the rock, and sometimes she just sits right down on it. In relation to this behavior the Wild Male's hump has gotten large in the last day and has reddened.