Originally Posted by reignOfFred
I think variables need to be looked at seperately and CatB makes a point.
First, it depends on the fish - Some are shyer and more timid and more reliant on higher numbers than others, and some types can get aggressive in low numbers while others stay peaceful. Some are very tight schoolers, while others are loose groupers. Some will continue to be active and peaceful in low numbers, others get shy and stressed.
Second, we can look at the tank size. 6 neons in a 15 gallon tank is much different than 6 neons in a 150 gallon tank.
Third, we can in some cases look at tankmates - maybe 6 serpaes will work fine as the main population of the tank, but when I kept them with a 9" nicaraguensis cichlid I ensured a nice group of 20 to instill confidence with such a big, albeit harmless, fish in their midst.
I had a group of white clouds for about a year but wasn't really into them, so I gave them away. After the taker left it turned out I missed one. He lived in that tank for 3 more years, the only of his kind, in a tropical tank, and he grew big and was always out and about. Would I purposely buy just one - not at all, but it is just case and point that not all schoolers/groupers suffer in small numbers, or even singly.
I also had a single Pygmy corydora for a few months, and he was active and constantly swimming and foraging and never once showed signs of stress. now, of course, he has a group because despite my playing the devils advocate I only keep grouping fish in groups, but just another example that while the fish may not be able to display their full grouping behaviour, saying the fish will automatically suffer alone or in tiny groups is short sighted.
i feel like this basically says it all.
you make a good point about the tank size and tankmates; a smaller group in a smaller tank is a lot different than a smaller group in a bigger tank, where they would basically get lost in their surroundings, and ten tetras in a tank with a mating pair of apistos would be a lot more shy than they would if they were by themselves.
good topic analysis right here.