Where did the rule of 6 for cory group size come from

[Reefmonkey]

It seems to have become conventional wisdom in recent years that corys must be kept in groups of at least 6 fish of the same species, to the point that there is an implication that to do any less is irresponsible. Yet those of us who have been in the hobby for a long time remember a time when the guidance was less...dogmatic?...about this, that pairs were fine, that smaller mixed species groups were fine. And we may have known a pair of corys or even a solitary cory that lived many healthy years. I understand that corys are often found in large shoals in the wild, but then again so do a lot of other species that are considered okay to keep even as solitary specimens. So I'm just curious, can this "Rule of 6" for corys be traced back to a specific source, like a peer-reviewed paper that actually studied corys in capitivity and found a minimum group size for health?

[Tetranerd]

I cannot find a “scientific reference” stating size of group, but over 40 years of fish keeping I have read that social fish like large groups for socializing and pecking order. The higher number of fish means that itriatble fish have more targets for their outrage.
And we all know that stressed fish tend to get sick. Less stress and good food and water, that’s what we can try to cont in their environment.
I have kept about 12 different cories. They always do well with a lot of other cories in a group, even mixed species of cories). Any that I wanted to breed went into a species only tank with snails and shrimp. I have kept a few in small groupings of three to induce spawning (1F,2M). But otherwise I have always kept them in groups of 5 or more when possible.
Ian Fuller has a great website, and he was/is routinely collecting in Peru. He has a website with a newsgroup. And I think planetcatfish is another good forum to inquire about your question.

Hope I helped and didn’t waste your time.