A large sample of otoliths from bigeye grenadier (Macrourus holotrachys) caught as by-catch in the Patagonian toothfi sh (Dissostichus eleginoides) fishery in Subarea 48.3 was measured and weighed, and the usefulness of otoliths as predictors of fish size was determined. Otolith mass provides good estimates of fish length, whereas otolith length and width measurements provide less accurate estimates of fish length. Seasonal variations in fish mass with reproductive condition need to be considered if predictions of fish mass from otolith mass are undertaken. Otolith size/fish size models should be derived for each fish population under investigation. The length of fish chosen in such studies should be representative of the size range consumed by predators.