An extensive 3D-mesh of O2-probes was deployed in a cage and allows an overview of the O2-content in the whole cage volume. This O2 distribution is statistically analyzed and its gradients discussed in time and location. In addition, current meters and a current profiler allow to discuss the oxygen data in the right context. Due to technical complications and environmental conditions the conclusion for a most representative O2-measurment point is difficult and less universal. Indeed it appears after analysis of the actual dataset, especially the flow data, that is even more complex to give a general statement regarding such a location as expected. Nevertheless knowledge of the processes within the cage has been gained and a wide knowledge base for further experiments of this kind has been generated.