They do exist, but I've never played with one. I think the only artist I have ever heard who used a bass trem is Les Claypool. I believe Kahler made them in the 80s, not sure where you get them now. Time for a google search!
Well, there's one company that makes them nowadays. Seems a little unnecessary to me, but hey, I never got so into bass playing that I thought "Man - I am limited by the fixed pitches on this intrument". Just the ole 2 cents
You are correct sir! So I guess technically I was correct in a mistake - how bizarre... he was using "tremolo" in its actual meaning, I was using it in its ass-backward guitar meaning... and hilarity ensued.
Never tried a vibrato effect (what is technically tremolo) with a bass, sorry
You and Creep both beat me to it. One of the great electric bass lines (and players) in prog-rock. Crank it up for full tremelo effect. BTW, I believe that Squire adds Moog bass pedals at the end of that tune when performing it live. Bone-rattling cool.