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everyone knows the "rule of thumb" of 1"/G.
is it a phisiological max or psychological max?
if it is phisiological, then the filter is more important than the size of the tank.
if it is psychological, then how does it change when adding plants to the tank?
how important is whether the fish are schooling fish or loners?
how important is their territoriality? their neighbours?

is there any data on this question (most compatibility databases are calculating water parameters rather overall behavior).

i have a big filter, moving 20 times the volume an hour, and i'm going to experiment with this (luckily, psychological stress doesn't kill as fast as poisoning)

I know this much, the 1" per Gallon rule is bunk. The size and "volume", ie thickness, of the fish alonfg with its territorial habits are more important than a simple length measurement. Hopefully, someone more knowledgable than myself will elaborate further.

-greg

I wouldn't really consider myself "more knowledgable", but I will definitely back up your argument.

Both physiological and psychological factors limit what and how many fish you can keep in your tank. Each species requires an appropriate amount of space depending on their size and activity level (free-swimming vs cave dwellers, etc.) to meet their physical needs in an aquarium. Their psychological needs designate space requirements as some fish prefer to school (thus requiring you to have enough tank volume to support a decent sized group), while others hold territories, and some species avoid other fish altogether and seek solitude.
How you arrange your tank as far as plant location, rock caves and driftwood will aid in managing space by providing for each individuals habitat niche. Cave dwellers will obviously stay in the caves while free-swimmers stay in the open areas.

As for which of a fishes needs are most important? All of them. If a schooling fish is kept by itself, it will waste away from stress and isolation. Or, if put with tank mates of a different species, may become aggressive. If to many aggressive fish are kept together, fights will constantly break out, or a some of the fish will become submissive and be beaten and denied food by dominant tankmates.

Anywho, I'm getting wordy. Is there data? Yes, tons of variables to go by. It would take a whole book to cover, and that's not even going to great detail. The best way to answer these questions of yours is to research the fish you hope to be keeping and plan a tank that fits their physical and mental needs. Fish each have different personalities and will act slighty different compared to others of their own species. Only through research, experience and good observation will you be able to catch a feel of how fish survive or even thrive in aquariums. You're asking lots of questions, which is good, but don't forget to look for knowledge on your own as well. Check out multiple, reliable sources. That is the best way to get a good grasp of a fish's requirements aside from keeping the fish itself. Good luck!

thank you both on your replies.
so basically i think i'll get the fish, and observe. if they're wrong in that community, i'll take them back.

i'll try to report back any observation i've got.

please, do the same too.

thanks

Actually it's best if you do research first, then buy and observe. It'll save the lives of a few fish and a few trips to the LFS.

Given the size of your filter, find fish that enjoy a strong current and avoid fish like bettas who like still waters.

Mostly, the idea is physiological, but with some fish, especially territorial ones, it can become psychological. An example I use is Red Tailed Sharks. Red Tailed Sharks hate their own species, and if two are in a tank (for this we'll use a 55gallon), they will fight until one dies. BUT, it's been found that if you keep a MASS of them, somewhere around 25 in a 55 gallon, they won't fight to the death. They will still look very pale all the time and die slowly. This would be an example of psychological stress making them weaker than they normally are, thus causing them to be more susceptible physiologically to their difficult living conditions...

PM/email/msg me if you have any questions/comments regarding me or my knowledge or if you want me to read a thread.