The ‘big old fat fecund female fish’ (BOFFFF) hypothesis suggests that larger, older female fish contribute disproportionately more to the reproductive potential of a population than smaller, younger female fish. As fishing typically differentially removes larger, mature fish, this can negatively impact reproductive potential and impair recovery of a depleted stock. In this study, the BOFFFF hypothesis was explored quantitatively for the West Australian dhufish (Glaucosoma hebraicum), a depleted stock exhibiting slow recovery. Size effects on population reproductive output of G. hebraicum were examined by determining the relationships between total body length of females with spawning season duration, spawning frequency and oocyte size, all of which were found to increase significantly with increasing length. Using per-recruit analyses considering fishing mortality values over a wide range, stock reproductive potential was always estimated to be higher when size effects on reproduction were ignored than if included. Fish stock assessments not considering BOFFFF effects (if these effects exist) thus have the potential to result in harvest rates being set too high which, in turn, can affect stock sustainability. Very low abundance of older, larger mature females (i.e. BOFFFFs) in the G. hebraicum stock is likely an important factor contributing to its slow recovery.