Light microscopy images of stained-transverse sections of the gills from juvenile Arapaima (Arapaima gigas) at different developmental stages. This fish, native to the Amazon River, develops a modified swim-bladder to transition from water to obligatory air-breathing as a response to hypoxic conditions during the dry season.  Dr. Andrea Frommel, a postdoctoral fellow with Dr. Colin Brauner, Department of Zoology, studies the development of fish organs and health examining the impact of habitat and climate change.