RES have been introduced and subsequently created populations all of the way up to the Great Lakes and the St. Lawrence seaway.

One advantage of introducing a fish species into your pond beyond the geographic range where it will "thrive", is that it should NOT act as a big factor that tends to strongly shift the existing balance in your pond. Barely reproducing and growing slowly might actually be desirable traits in your pond.

If you can get some RES for a reasonable expenditure of time and money, then they are certainly one of our best tools for snail control. If the worst outcome is that they do not manage to recruit in your pond, then you will become our PB expert on the northern range of RES.

In my non-expert opinion, all fish species have their "preferred" foods, but still tend to be pretty opportunistic. If yellow perch or trout can pluck snails for a meal with a very low expenditure of effort, then I suspect they would also make at least a dent in your population.

If you analyze what new species addition would go best with your existing pond balance of species, you might just try that experiment. If your snail population keeps increasing, then you may have to then go to Plan B.

RES and yellow perch have a very low likelihood of taking over your pond. The trout could probably never take over your pond, unless you never catch any of them and they get very fat and happy and take up too much of your fish "biomass" percentage.

I can't remember, what is your existing fish population and goals? If you add that, the experts may drop in with some better responses.