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In the modern ocean, waters with <20 μmol kg-¹ of dissolved oxygen are known ⁻ as oxygen minimum zones (OMZs) and occupy ~1% of the global ocean. Zooplankton plays an important role in marine ecosystems, as a trophic link between primary producers and larger animals. Zooplankton is also an integral part of the biological carbon pump. Diel vertical migrations (DVM) between midwater depths at daytime and surface waters at nighttime is a unique process conducted by zooplankton in the ocean that impacts ecological interactions and nutrients cycles. Zooplankton DVM can be responsible for the transfer of a significant amount of carbon and nutrient from the surface to depth. Most available data on the vertical distribution of zooplankton rely on vertically stratified net samples with relatively thick integrated depth strata sampled. Above the intense OMZ off Peru, the upper oxycline is viewed as the single most important barrier structuring the water column. Up to now, the fine-scale distribution of zooplankton relative to this barrier has not been resolved in detail. In the present study, I determined the fine-scale vertical distribution of zooplankton abundance and biomass and its correlation to O2. During the cruise, zooplankton was collected at eight stations in different O2 strata from the upper OMZ to the surface using a towed Hydrobios multinet, with three nets sampling the oxycline (which was often only a few meters thick. At the same stations, vertical hauls with fixed depth intervals (1000-600-300-200-100-0) to a maximum of 1000 m depth were conducted. Zooplankton >500 μm from the trawl hauls and >1000 μm from the vertical hauls were used for the data analysis. The oxycline (Zoxy) and thermocline (Ztherm) in the OMZ off Peru ranged between ~20-50 m and were shallower at onshore compared to offshore stations indication of higher biomass distribution but similar abundance. In terms of abundance, calanoida and eucalanidae copepods are the most dominant organisms in the system. However, both in terms of ...