A large spawning aggregation of Polymixia lowei, Beardfish, was documented via video and specimen collection in a deep-water (413 m) sinkhole off Key West, Florida on 5 June 2007. The use of the human-occupied submersible, Johnson-Sea-Link II, allowed for in situ observations, video documentation, and specimen collection. The maximum density (117 fish m⁻²), average abundance (56 fish m⁻²), and average standard length (152.1 mm) were estimated from video transects. Ovarian histology of the fish collected indicated recent spawning activity. Observations of a deep scattering layer above the sinkhole by echo sounder suggested that P. lowei were in the water column during the pre-dawn hours. This represents the first report of aggregating behavior for reproduction in P. lowei.