I use my MTB to fish also, have for five years now. The only time I do is up in northern Michigan, flyfishing for trout; I’ve never tried it around home. I wear my fishing tackle (flyfishing vest), put the rod in its case w/sling across my back, and carry my fish in a creel slung over my shoulder if I keep any (usually catch-and-release). If it’s warm, I wade wet and just bike in my Reef Runners. Otherwise, I can ride in hip waders (what a sight!), or roll up my neoprenes and bungee them to the rack. I drilled and tapped the dropouts on my new Klein for a rack just so I could do that.
It looks Fred, but does the job. I can get to parts of the stream in half an hour that would take two or three hours of walking, so I fish where the fish are dumber 
Even where there is jeep-trail access I ride any more, because I can go twice as fast down those gawd awful trails on my MTB as I could in my Jimmy. Then keep right on going on the single track when the jeep trail ends. I also bird (“birdwatching” to the non-birders out there) from the bike. An MTB is the absolute greatest birding transportation ever! Cover miles of habitat in a quarter the time, no noise, no pollution. Best of all, for some reason wildlife doesn’t seem to identify me as “human” on the bike. (Neither do some humans…)
As long as I stay astride, I can approach more closely without spooking than I can hiking. You know, Lee, there is a guy who is always downtown (mostly seen around World Trade Center building) who rides a bike and wears rubber waders– but on a year round basis, even in JULY and August in New Orleans– he is, however, half a bubble off plumb!! (allegedly an ex-computer hack, totally paranoid, says government keeps tabs on EVERYONE and wears waders b/c thinks levys are a plot or something!) ObFishingMtnBike: Been there, done that, got the t-shirt. OK, sort of. Going swimming in closed quarries in Ohio– lots of blue gills like to suck dead skin cells off legs.
