As a general rule, the owner of a business should not be tipped, and employees should be tipped according to the quality of service they provided. As with anything to do with fishing, you can not go by general rules.
One problem is many guides are the owner and only employee. They should only be stiffed completely if the service was sup par. a small tip if service was average, and the sky is the limit if the service was exceptional. You should tip for the service, not simply by the size and numbers of fish caught. A lazy guide can have a lucky day and catch you fish, but a good guide will never give up if fishing is slow and give you extra time on the water if that what it takes to get fish in the boat. You should learn something from a good guide, and feel like you would want to fish with them again, regardless of size and number of fish caught. If you feel like you would not want to fish with them again, then they did not do their job. They should be able to provide exceptional service for any factor they have complete control over, such as lunch, drinks, safety ,boat handling, teaching ability, and general comfort. The factors they can't control like making the fish, bite they should demonstrate exceptional knowledge, skill and do their very best.
All the outfitters, I have worked for both hunting and fishing would give any tips they got to their staff. If the owner is the only employee, than they probably depend on tips to keep in business, and you should tip something unless they did not live up to the service they promised when you booked the trip, were rude, didn't try their hardest to get you fish, or you simply did not enjoy your day.
Tipping is a very personal matter, and no one but the fisherman can determine what they should tip. I have had clients that tipped almost nothing for unbelievable days in the field, or on the water. I look forward to taking these anglers out year after year regardless of how much they tip. I have had others, that tipped far more than I expected, but I would dread having to ever take them fishing again. Remember guides usually guide for the love of the sport, and hope to some how make a living. For every great guide, there is a great client, and for every poor guide their is a poor client. I have always tried to be a great guide, and if you want to be a great client, a big tip may help, but being a fun person to spend a day on the water with is more important.
A good guide will know the fishery like the back of his hand, not be intimidated by sub par weather, or water conditions, and be be able to adjust to any skill level of angler. They will be an excellent teacher, and a fun person to spend a day on the water with. If he or she does all that, then a generous tip is a great way to show your appreciation. What you think is generous is personal, and will vary from anger to angler. If your guide works for a lodge or outfitter, the owner should be able to give you an idea, of what they consider and average tip. Please never ask the guide how much to tip. It makes for a very awkward moment, and most guides will simply say whatever you want and you haven't found anything out anyway. Also, guides can always use and appreciate any gear from lures to waders, and most wont turn down a beer at the end of the day.