This dataset compiles fish length and weight measurements from the RMT-25 net hauls carried out on Discovery 2010 cruises (JR161, JR177, JR200) in the Scotia Sea, Southern Ocean in spring 2006, summer 2008, and autumn 2009. The dataset comprises of the station net hauls only. Research cruises were led by British Antarctic Survey aboard the RRS James Clark Ross. Net hauls were conducted along a transect from the Antarctic Polar Front to the sea ice zone in the Scotia Sea. Hauls included in this dataset are depth stratified (1000-700 m, 700-400 m, 400-200 m, 200 m to surface). Individual fish lengths, and weights were measured on board. Where weights were not measured, length-weight regressions have been used to estimate fish weight. This data set accompanies the paper by Belcher et al. in Marine Ecology Progress Series, titled, Respiration rates and active carbon flux of mesopelagic fishes (Family Myctophidae) in the Scotia Sea, Southern Ocean.