what causes a fish to turn white?

I recently floated the Big Springs river with my family. I was enjoying watching for and and finding fish. I seen one fish that appeared to be half white, with what appeared to be a vertical line at the dorsal fin. I paddled back up to see if I can see it again,then I seen the opposite side and it was all white except for the head and tail. The shape seemed like a trout because of the light color I was thinking Golden, but I very well could be wrong on the type but the white fish I am sure of. What did I see? or what caused the white fish?
Answer: 
What you may be seeing on the fish is fungus from a wound on the fish.  Many times, when herrons or pelicans attempt to catch a fish and miss, there will be injuries on both sides the fish where fungus will grow.  Once established on the fish, it can spread and can cause eventual mortality.  The other thing is sunburn.  Yes, fish do sunburn in clear, shallow streams.  The lighter skin pigments will darken with time.
Answered on: 
Friday, August 1, 2014 - 12:01 PM MDT