I have never kept a solitary one. I actually keep a lot in a single tank right now, but when they are mostly half-grown fry, there isn't much one can do. I only hope that 36g is enough space for the 34 fry and two adults. I have noticed that the adults tend to withdraw and remain on their own or in a pair while the young are far more social. Do I think that 34 social cherry barbs is entirely normal, probably not, but the fact that they have been raised together and know of nothing else can be a contributing factor to their increased sociability. Unfortunately, my fry are not yet old enough to distinguish sexes, so I'm not sure of my male:female ratio
I still think a trio, or even just a mating pair, of cherry barbs is a great addition to a peaceful community aquarium. If they are kept in such numbers, or even singly, however, there is then the implication that a cherry barb will thrive in a small tank. True, they are small fish, but I have found them to be rather messy. In some ways, I have find them to be like miniature goldfish. I successfully kept a pair and an oto in an 8g tank, but it was very densly planted. I guess you could put a trio in a longish 5g, assuming that the tanks was again densly planted and the water quality was well maintained, but that would be pushing it. The males can be persistent when pursuing a mate, and jumping the tank (it was an open-top, the 8g) was the cause of death among females. There just wasn't enough space for the female to find refuge and a second female only got in the way.
I am only speculating at this point and I am by no means an expert in Cherry barb biology or behaviour. I think between 8-10g is sufficient for a breeding pair with clean-up crew, especially if there is a place to house growing fry. Perhaps 5g is even fine for just the pair, especially if it has a tight-fitting lid, and is long rather than tall. It would be interesting to see if you could apply some cichlid rules regarding stocking to cherry barbs, say an adult breeding pair or trio for every 10g of water or so. I am not certain.
Sorry I wrote so much in your thread, but since I'm breeding these guys, it has been interesting to observe their behavior and learn what has proven most successful for my fish.
Warmest regards, and others are by all means welcome to jump in and correct me if I'm way off.
llj