It almost doesn't matter what the thing is; it's shape tells you it's a fast water fish, and most fast water fish need cool, oxygen rich conditions. Assuming it was sold as a "tropical" fish, it doesn't matter much whether it is Stiphodon (a goby) or Characidium (a tetra) -- all these fish need much the same thing. Relatively low water temperature, fast flowing water, lots of oxygen, and a diet much like that for a loach: insect larvae, small crustaceans and algae.
If it has two, separate dorsal fins, then it's an "advanced" fish such as perciform or a goby. Characins (tetras) may have two fins on the back, but one is a regular dorsal and the other a tiny, spineless structure called an adipose fish. Gobies will have fused pelvic fins that form a sucker-like structure. Sleeper gobies (Eleotridae) look like gobies but have regular pelvic fins. Mystery sleepers and gobies turn up all the time in pet shops, often under fanciful names such as "freshwater neon goby" and the like.
True darters (genera Percina, Etheostoma, etc.) are not common at all in the global ornamental fish trade, and even in their native North America they are kept mostly by people who catch their own fish. You're unlikely to see them in pet stores in Canada or the US, but I suppose anything is possible! Various species, some temperate zone, others more warm temperate, borderline subtropical, so it's a good idea to try and identify this fish if a true darter it turns out to be.
Cheers, Neale