That the predominant by-catch of grenadier by the toothfish fishery in the Ross Sea region is comprised of two species, rather than being solely Macrourus whitsoni, was recognised in 2010 with the identification of a new species, M. caml. Grenadier are the main by-catch in the toothfish fishery and modelling suggests that they may be subject to predation release as the abundance of toothfish reduces. In order to improve information on the spatial distribution, age-frequency and relative importance of grenadiers as prey to toothfish, a method of distinguishing between otoliths of the two species was sought. Based on 220 M. whitsoni and 307 M. caml otoliths, a linear function of fish total length, the depth of the otolith and the otolith vertically projected area gave excellent discrimination between the two species (92% success). A method was also developed to discriminate between otoliths of M. whitsoni and M. caml using otolith parameters alone. This method correctly identified 90% of otoliths to species and could be applied to otoliths removed from toothfish stomachs to estimate the relative consumption of the two species of grenadier. Models to estimate fish length, weight and age from otolith parameters are also presented.