Animals control locomotion through unpredictable and complex habitats using a single locomotor control system. Because of the disparate physical mechanics of different environments, behavioural plasticity, based on the complex interplay of sensory feedback and environmental constraints, is likely essential for animals moving across environments. However, few studies have investigated neuromuscular control across different environments. To fill this gap, I make use of Polypterus senegalus to address four primary objectives: (1) to explore the extent of neuromuscular plasticity across environmental gradients (viscosity and water depth), (2) to generate and test hypotheses about paramount signals for this neuromuscular plasticity, (3) to determine the neuromuscular underpinnings of locomotor transitions, and (4) to determine the neuromuscular control of developmental behavioural plasticity in novel environments. I measured the kinematic and muscle activity response of P. senegalus to gradual changes in environment forces using gradients of water viscosity and water depth. I then used a semi-intact preparation to investigate the existence and role of the mesencephalic locomotor region, a brain region that controls locomotor speed and mode in other species, for neuromuscular control in P. senegalus. Finally, I used chronic terrestrial acclimation and exercise to determine the neuromuscular underpinnings of behavioural and morphological plasticity previously seen in P. senegalus reared in a terrestrial environment. I found that in high viscosity environments, P. senegalus maintain routine swimming speed using a swimming-like muscle activity pattern with increased effort in the posterior body and the pectoral fin to generate exaggerated swimming kinematics. These results suggest that sensory feedback is essential to accommodating this novel environment. I then demonstrated that axial red muscle always carried an anterior-to-posterior wave of muscle activity in a series of discrete water depths across the aquatic-terrestrial transition. Thus, discrete changes in axial kinematics and pectoral fin coordination across this transtion are likely the result of sensory feedback and mechanical constraints of the environment. I then performed the first experiments searching for the mesencephalic locomotor region in P. senegalus and demonstrated the presence of a putative mesencephalic locomotor region that controls the frequency of swimming-like movements but does not appear to control pectoral fin movements or the transition to walking. Finally, I exposed P. senegalus to chronic terrestrial acclimation and exercise. My results suggested that while both terrestrial acclimation and exercise generate behavioural plasticity, the former results in a larger plastic repsonse. Subtle changes in the duration and timing of pectoral fin muscle activity helped reduce friction between the body and pectoral fin and the substrate below, potentially resulting in the more “effective” walking gait developed by terrestrial acclimated fish. My thesis therefore sheds light on the essential interplay of sensory feedback and mechanical constraint for generating behavioural plasticity on acute and chronic timescales, highlights the potential value of such plasticity for organismal performance and evolution, and develops study systems and experimental frameworks for further investigating the nature of plastic locomotor control in amphibious fish.