My thought on this topic are like this! If your on a trip that might have your guide or captain, and a first mate. I would think a good tip to the first mate would be something you would definitely want to do but still your choice. the captain would not get a tip regardless his pay should have been in the cost of the trip!
on trips where its just you and the guide then I would tip well to the guide that made the extra effort to say help my kid catch more fish so I could focus more on fishing myself. This guy gets a good tip!!
otherwise I say do what feels right. If you feel obligated to tip but dont think one is necessary then dont tip.
Like some of the guides have stated tips are always something anyone would appreciate but I think most small guide dont expect you to fork out extra.
Heck most of us are on tighter budgets these days, If a tip is expected that just may mean the guides wont be working as much..