Comments: Gambusia holbrooki from east of the Mobile River formerly was regarded as a subspecies of G. affinis; holbrooki was elevated to full species status by Wooten et al. (1988); this change was adopted in the 1991 AFS checklist (Robins et al. 1991). Page and Burr (1991) retained holbrooki as a subspecies of affinis, noting intergradation in the Mobile Bay basin. Gambusia affinis apparently hybridizes/intergrades with G. holbrooki in some sites in the Chattahoochee and Savannah river drainages (Lydeard et al. 1991).
Member of subgenus Arthrophallus, affinis species group (Rauchenberger 1989). See Rauchenberger (1989) for a study of the interrelationships of the subgenera and species groups within the genus Gambusia. Some southwestern populations of G. affinis were regarded as a distinct species, G. specioisa, by Rauchenberger (1989); Robins et al. (1991) viewed them as, at most, a subspecies of affinis.