Given good water conditions perch can and will quickly multiply to the point of being the largest numbers in the system. I've seen where even the little ones (6"ers) have roe. They are prolific reproducers, kinda like underwater rabbits 
Our lake has no limit on perch, it is somewhat self imposed by the number you need for a meal or how many you want to clean. I've brought 30 home and not even had one male in the pail.
Ditto. You can't over fish yellow perch. A very prolific species and impossible to get rid of once they are introduced short of rotenone. However I've seen at least one case where that didn't even get rid of them all.
Interestingly since I hatch my own perch now in a separate pond I have perch that are sexually mature in only one year. Of course they are much larger than they would be in the wild at up to 8 inches at only 1 years old.
