You're referring to Puntius Denisonii. Yes they are a beautiful fish.
I have a school of 20 in my 175 gal. tank.
They get along just fine with all the other fish, including Danios and plecos, no problem at all.
They look good with a school of Scissor Tail Raspboras as well, kind of like a black and white version of the denisonii.
They're very hardy and do get a little on the large size. My oldest ones are 3 years old now and they're about 5 inches long including tail.
They are a schooling fish so you should have at least 6.
By the looks of it, this would be the sixth type of fish in your 55 gl. You'll want to take care not to crowd the tank.
Your tank is semi-planted (?), how much filtration do you employ?
The more fish, the bigger the canister you need.
