10-02-2011, 02:43 PM
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Brownmane is correct in both posts. Corys occur in very large groups, hundreds, naturally; in some creeks there may be more than one species, but there are always hundreds of each species. I tend to prefer buying a minimum of 3 of each species when I can, and if it is a species I particularly like I try to get 5-6. I have almost 40 corys in my 115g now, with several species, so getting just 2 or 3 if that is all I can is not an issue as they have other corys around them, and this seems to be the main issue. It is interesting how some will remain closer regularly, others seldom. But when stressed, as they were when I moved them recently in order to re-do the tank with sand, they clearly remained in their species groups for days after. So there is a definite plus to having more. Much the same as with most shoaling fish (tetra, rasbora, etc)--just having more of their own species in the tank will settle them considerably, even if they do not seem to be together a lot of the time.