Developmental maturation occurs in slow swimming behavior in larval zebrafish; older larvae acquire the ability to perform slow swimming with keeping their head stable in the yaw dimension. A class of long-distance descending commissural excitatory V0v neurons, called MCoD neurons, are known to develop at later phase of neurogenesis, and participate in slow swimming in older larvae. This led to a hypothesis that MCoD neurons play a role to coordinate the activities of trunk muscles in the diagonal dimension (e.g., the rostral left and the caudal right) to produce S-shaped swimming form, which would contribute to the stability of the head. Here, we show that MCoD neurons indeed play this role. In larvae in which MCoD neurons were laser-ablated, swimming body form often became one-sided (C-shaped) bend with reduced appearance of normal S-shaped bend. With this change of swimming form, the MCoD-ablated larvae exhibited greater degree of head yaw displacement during slow swimming. The long-distance descending commissural V0v neurons are implicated in playing roles in diagonal interlimb coordination during walking in mice. Together with this, our study suggests that the long-distance descending commissural V0v neurons form an evolutionally conserved pathway in the spinal locomotor circuits that coordinates movements of the diagonal body/limb muscles.