I found an article titled, "That Sinking Feeling" at
http://www.bcadventure.com/adventure/angling/protalk/rowley/sinking.phtml. In the article the author talks about how he caught a trout and then used his
trout pump to pump the stomache contents out so he could see what the trout were eating. I guess the idea is to see what the trout are eating and then use flies similar. I have heard of gutting the first fish you catch and then looking in the stomache but this takes the cake. Pump the trout's stomache so you can release it? I thought the whole idea of catch and release was to do no harm to the fish so they can get bigger or make more fish.
I have heard and read articles about using a small net or seine to poke around under rocks to see what aquatic insects there are, but I find it hard to believe that someone is willing to pump a trout's stomache to catch more fish. To me, that's crazy.