Absolutely no idea... I don't even keep count on individual trips. If clients want to count, that's fine. I gauge trips based on "level of fun," not "number of fish."
However, if I was forced to come up with an educated WAG (emphasis on WAG) ... I would conservatively say an average of 8 - 10 fish per trip. And as a part-timer, I'm doing about 50 - 60 catfish trips per year (doesn't count crappie, bass, bluegill, etc.) This is my third year guiding, so you do the math. (FYI, first year the numbers were huge. 2006 was an incredible catfish year. Last year and this year have been more average.)
Numbers also vary widely depending upon if we go fishing for "quantity" or "quality." In the last two weeks I've been on a "quality" bite.... the numbers have been low... six trips probably averaging 4 or 5 fish per morning (best morning was 8). All of those fish were at least in the 10-to-20 lb. class... four in the 20-to-40 lb. range and one that was 61 lbs. I'd say in the last six trips we've put nearly 400 lbs. of catfish in the boat.