Well, that question can be taken many ways, but we need to define what 'blackwater' is.
In short, it is pretty much a tannin saturated location stream/river with relatively low flow.
By that definition, it would be hard to say that these types of systems are only in tropical areas, which, surprise, they aren't.
An example close to home for me is the Ocqueoc River, or the Tahquamenan River. Both are considered 'blackwater' due to their slower flow and heavy concentration of
tannins (according to wikipedia).
As for temps here, I have seen snow in June, 70F and sunny on Christmas Day, 120F in July, and -35F in February. I call it the Bipolar State, where you can quite literally experience 4 seasons in one day. Come april its 35F at 7am, but by 1pm its 80F out, I am literally not kidding. Pretty much as far from topical as possible.
Now the fish in these rivers are basically the same as all the other rivers and lakes. Muskellunge, Pike, Bass, Bluegills, Shad, Crappie, etc.
You could consider them blackwater I suppose, but people with well water here say its so hard the common term is 'Liquid Rock' (Like
GH-18+ and KH-18+).
The truth is that most fish are very adaptable and living in a
pH of 6.5 vs 7 vs 7.5 or 8 really doesn't matter too much. The major reason is stability.
Most fish could do blackwater conditions, but I would avoid those who really need the extra electrolytes to thrive, like cichlids, livebearers, puffers, etc.
