If Eq. (7.3) were the correct generalization of Eq. (7.1) to a curved spacetime, how would you

Question:

If Eq. (7.3) were the correct generalization of Eq. (7.1) to a curved spacetime, how would you interpret it? What would happen to the number of particles in a commoving volume of the fluid, as time evolves? In principle, can we distinguish experimentally between Eqs. (7.2) and (7.3)?
Eq. (7.2)
(n Uα);α = 0.
Eq. (7.3)
(n Uα);α = qR2,