You have understood the main idea - do not let that fish feel uncomfortable. When you bring some fish to pond (lets say that you carry them in a bucket) then compare temperatures. A scientist once released brown trouts in a river and he said that fish needs 1 minute per 1 degree (Celsius) to get used to the new life.
I mean that he added some river water and waited a bit. Then added some additional water and another minute of waiting until temperatures were equal.
[In case something's wrong and your fish are suffering from lack of oxygen during transportation process, you better release them immediately. Fish might get some temperature shock but at least they will get enough oxygen.]
After releasing fish might get confused and don't be surprised if your trout shows no will to swim away. It needs some time.
Some wise guy once said that he never releases trouts that seem to be feeling bad. Some other fish may recover but trouts are more sensitive and they probably will die.
I don't know about scientific proof of this - do it or not on your own risk.
By the way, a video about releasing small brown trouts (
http://www.nomad.lv/?p=4826). It's in Latvian but the language isn't that important. Simply watch and see how this guy does releasing (from about 16:30) - add a bit water, wait and do it again.