Invisible Red

My wife caught a monster Red Snapper in the Pacific Ocean off of Costa Rica a few years back - pretty incredible. The waters down there are are crystal clear, you can see whales swimming 100 feet down. The Snapper are born in the rivers of the rain forests and when large enough, venture out to sea - really cool. You can sit in the the river mouths and fish for the snook waiting for the pre-teen reds to go salty - super incredible. Anyway, I was wondering why a fish so tasty would be red, and I remembered 2 things: more and more fire trucks are being painted chartruese and The Fisherman's Ocean by David A. Ross. He explained how the color red diffuses and disappears in the water as you get deeper. This explains Cajun Line - a new red line that is magical - I have just spooled some on my spinning rod and it looks cool, in a new and evil way.