A sample of 36 Gnathophis mystax (Delaroche, 1809), 198 Conger conger (Linnaeus, 1758), and 61 Muraena helena Linnaeus, 1758, caught with longlines or by trawling in the coastal waters of northeastern Tunisia, was collected from December 2008 to December 2010. In both congrid species, G. mystax and C. conger, otolith mass and fish length are strongly related by a power function, with high correlation coefficients (r = 0.885 and 0.927, respectively). However, for M. helena the r value is significantly lower (r = 0.79). The same is true for the relationship between the length of the anteroposterior axis of the otolith and fish length. In all three species, the relationship between otolith mass and fish length has an allometric coefficient b inferior to 3. Similarly, the value of b' is inferior to 1 within the relationship between the length of the anteroposterior axis of the otolith and fish length. In all cases, the calcified structures show a negative allometric growth. However, inter-specific differences are observed, which could be related to ontogeny and life-history traits of the species. [ABSTRACT FROM AUTHOR]