I am going to chime in here and say that it is recommended not to have more than 1 in a tank because they are known to be aggressive and territorial. They are not a schooling fish, so why would you want to have another of their species for them to be with? In the wild, they live in much larger areas than we provide in a tank, so they can establish a territory and keep other bgk's out of it (with the obvious exception of breeding). If a tank does not provide enough space to do that (which would be a HUGE tank), then no, IMO
you shouldn't keep more than 1 in a tank.
No, I do not think they swim together in nature with no consequences. Territorial fish are territorial in the wild as well as in captivity. In the wild, they fight, damage each other, chase each other out of territories, and things like that. In a tank, the loser cannot flee very far, so more serious damage can happen. IMO
/E, not all fish are social, so why try to ask them to be social? Some cats are solitary, some dogs are solitary, some bugs are solitary, some fish are solitary. IMO
, is it moral to ask fish to be something other than what's natural instinct and behavior dictate it to be?
Just my opinion.