As Bill said, they are probably all males. Reason being is that females would want to be breeding and holding eggs and thus not eating, so they don't grow as fast as the males.
The smaller fish are what seems to be ravenous for FA. They are eating machines. If they are all males, makes it kind of a plus and minus. They will always eat(compared to females), but you will not get any hatches which is what really munches on the FA.
I think the food market likes Red Tilapia, which makes them less cold tolerant, thus a shorter FA eating season.
