An update of the checklist of fishes of Alligator Reef and environs some fifty years after the first listing provides an unparalleled opportunity to evaluate the species richness for a limited reef area, as well as a unique opportunity to explore changes in diversity over a half-century time scale. We added 107 species and subtracted 5 from the original total of 516 species: thus the checklist is now totalling 618 species, of 122 families, the most recorded for any similarly sized area in the New World. The additional species records are made up of more recent identifications from the original sampling program (and a limited number of subsequent collections), as well as from a comprehensive effort by the junior authors to photograph the fishes of the study area. The latter project has provided 35 additional species for the checklist (plus 4 from others), from 318 total species photo-documented. The photographic records are presented and archived for reference. The checklist is analyzed in detail, taxonomic changes summarized and presented, and the list is compared to more recent compendia of fish lists for the Greater Caribbean region.