Age and growth of Gnathophis mystax (Delaroche, 1809) (Congridae, Anguilliformes), from the northern Tunisian waters

Thinlip congers, Gnathophis mystax (Delaroche, 1809), were collected from the south region of the western Mediterranean Sea (northern Tunisian waters) in order to determine age and to estimate growth parameters. The range in length was 15.1 cm-36.9 cm and weight was 9.5 g-61.5 g. Vertebrae and otoliths were removed from 42 individuals. Vertebrae exhibit the most interpretable annulus formations. The length-weight relationship was given by TW = 0.0004* TL3.273 R2 = 0.949 (where TW = total weight in g; TL = total length in cm). Age determined from vertebrae ranged from 2 to 7 years. Parameters of the Von Bertalanffy growth equation were L∞ = 86.3 cm, K = 0.102 year–1 and t0 = –0.27 year. Vertebra diameter was strongly correlated with total length and age. This study has provided the first published data on age and growth of G. mystax in the Mediterranean Sea.