In both Polar Regions, sea ice environments are undergoing rapid environmental change. Because sea ice constitutes an important habitat for numerous species, as well as an important carbon source during critical periods of the year, these changes impact significantly on ecosystem functioning, biodiversity, species distribution and population sizes, including commercially exploited fish stocks. Species dwelling at the ice-water interface (e.g. Antarctic krill and Arctic cod) play a key role in this context as trophic carbon transmitters from the sea ice into pelagic food webs, and ultimately to the deep sea benthos. Quantifying under-ice communities was hampered in the past by the inaccessibility of the ice underside to conventional sampling gear. Using a new under-ice trawl, it could be shown that Antarctic krill concentrates under sea ice almost year-round, and that krill dwelling under ice are significantly under-estimated by pelagic nets and sonars. An Arctic expedition in 2012 using the same sampling gear brought evidence of a vivid under-ice community even in the biologically poor-considered central Arctic Ocean. Using a bio-environmental sensor array during under-ice fishing enabled fine-scale characterization of sea ice habitat properties as a basis for statistical modeling of under-ice species distribution. During the talk, past results from under-ice fishing in the Southern Ocean will be summarized, and complemented by preliminary results from the Arctic Ocean to elucidate similarities and differences of polar under-ice communities in both hemispheres.