Here are some examples of the effects one can achieve on the tuba, including vibrato, trills and tremolos...
Vibrato is a slight undulation in pitch. It can also be a variation in intensity of sound. Either way the effect is of a sound that 'wobbles' slightly. Written instruction in the music - Vib. or Vibrato. Trills are a rapid alternation between two pitches - either a tone or a semitone apart. Tremolos are a trill or rapid alternation between two notes more than a tone apart.