The presented data here are part of a much larger study, in which we assessed the respiratory organ of the zebrafish with different methods; here we only report on the microtomographic imaging. After critical point drying, heads of 20 fishes were imaged on a
Bruker SkyScan1172 high resolution microtomography machine (Bruker microCT, Kontich, Belgium). Ten fish fishes were subjected to endurance training, ten fish were from the control group. A tomographic data set of each fish head was obtained in between 6 and 19 hours and with an isometric voxel size of 1.65 µm. We manually delineated the gills in CT-Analyser (Bruker, Version 1.17.7.2+) and exported the resulting volumes of interest as a set of PNG images for each fish. We used a simple threshold to binarize each VOI image into gills and background. The gill volume was then simply calculated as the volume of all the binarized pixels. The organ area was extrapolated by binary closing of the thresholded gill image and summation of said image.