Deep-sea fishes (inhabiting >200 m depths) are important marine prey and predators that play key roles in ecosystem connectivity through their biotic (trophic) interactions and movement patterns. Within the water column, vertically migrating micronektonic fishes (c. 2 – 20 cm in length) are a key part of the active Biological Carbon Pump (BCP) and important prey for a wide variety of predators, including nocturnal predators feeding on migratory fishes near the ocean surface, deep-diving predators feeding in and around the deep-scattering layer (DSL) during the day, and demersal and benthopelagic predators that feed on pelagic fauna occurring close to the seafloor. Through the DEEPEND and DEEPEND|RESTORE research programs, we have shown strong changes in the fish assemblage along vertical (depth) gradients across the northern Gulf, as well as changes correlated with the Loop Current. We attribute these observations to the relative strength of vertical biotic and abiotic gradients in deep waters compared to the horizontal plane, but it is also likely that the details of these patterns are affected by intraspecific variability within the populations. Size structuring is well-established in pelagic ecosystems generally, with individual body size correlating strongly with swimming capability, prey detection, predator avoidance, and energy storage, and ‘bigger-deeper’ trends are commonly reported for both migratory and non-migratory fauna. Here, we summarize the influences of key drivers influencing midwater fish distributions of the northern Gulf and present some preliminary analyses of patterns in body size