  The internal motions of DNA immersed in bio-fluid are investigated. The
interactions between the fragments of DNA and the surrounding bio-fluid are
modeled using the gauge fluid lagrangian. In the model, the bio-fluid is
coupled to the standard gauge invariant bosonic lagrangian describing the DNA.
It is shown that at non-relativistic limit various equation of motions, from
the well-known Sine-Gordon equation to the simultaneous nonlinear equations,
can be constructed within a single framework. The effects of bio-fluid are
investigated for two cases : single and double stranded DNA. It is argued that
the small and large amplitudes of a single stranded DNA motion immersed in
bio-fluid can be explained in a natural way within the model as a solitonic
wave regardless with the fluid velocity. In contrary the double stranded DNA
behaves as regular or damped harmonic oscillator and is highly depending on the
fluid velocity.
