i would say it's both ways. i will guess that the developers are required to stock the ponds with at least panfish and probably bass. basically they pay for it but have some company do the stocking or pay for the MNR to do it. it's probably a regulation when the developer has their project approved. now if there's a fish die off a few years later, who knows if the developer is required to restock it at their cost. the storm pond close to my house had hundreds of fish die this summer but i never saw that the 3 previous summers.
as for the variety of fish, who knows. since the developer is paying someone to do the stocking (i assume) that company or MNR could have decided to mix it up by putting multiple species of panfish. and add in the brown bullhead to help clean the bottom of the pond.
and i'm sure other species must have gotten in from a trib, whether it be a creek or through the actual storm drains. i've seen minnows and shiners and chub, etc. in parking lot puddles so i can only imagine what's below us in all the storm pipes and drains. especially after a storm/flood.
there are water diversion channels all over the place that we never pay attention to when driving right over them. you know, those really narrow concrete aqueducts that go on for miles that divert water from one place(s) to another. they have them running by malls like bramalea city centre or by GO stations like at bramalea or clarkson in sauga. i have actually stopped and looked at some of those at different points far, far from Lake O and seen minnows in them and wondered how they got there and where they'll end up next. one day i'm gonna see a big fish in one of them and i'm gonna catch it and have a great story to tell.
and as others have mentioned on here before, some eggs are carried by water fowl and seagulls, either by getting stuck in their feathers or from fish they were eating.
