Westfly has had some interesting discussions on this subject. One item that got my attention was the increased mortality of fish that had been removed from the water for whatever reason and then returned. Here is a quote from that study.


Exposure to air and mortality rate:
“Ferguson and Tufts (1993) reported disturbingly higher mortality among domestic
rainbow trout subjected to air exposure after mimicked angling events than for control
fish or experimental fish not exposed to air. Their data revealed 100% survival among
control fish and 88% survival among exercised (i.e., “angled”) fish. Among fish that were
exercised and then exposed to air for 30 and 60 seconds immediately thereafter,
survival dropped to 62% and 28% respectively. The authors stressed their results had
important implications for Atlantic salmon sport fisheries where the marked trend was
toward catch and release but where anglers habitually hold fish out of water for
significant periods of time prior to release"

Tim