  We derive the total helicity conservation law for a perfect electromagnetic
relativistic fluid. As the conservation equation contains the derivative of the
magnetic helicity, it can be reshaped as having the same form as the chiral
anomaly equation if the fluid is isentropic. We also take the non-relativistic
limit of the helicity conservation law, and check the agreement with the
Abanov-Wiegmann equation at zero temperature, but we provide further
corrections in the more general case. We then consider chiral fluids, when the
chiral anomaly equation has to be incorporated in the hydrodynamical equations,
together with other chiral transport effects which exist in the presence of a
chiral imbalance. We finally study how the chiral imbalance modifies the
helicity conservation law.
