Growth and age estimation of the greater forkbeard, Phycis blennoides (Actinopterygii: Gadiformes: Phycidae), from the Gulf of Tunis (central Mediterranean)

Background. The greater forkbeard, Phycis blennoides (Brunnich, 1768), is a gadiform species, which has economical value and its population is dwelling in a 60–800 m depth range throughout the Atlantic and the Mediterranean. Along African north coast, there is a lack of information about the biology (age, growth, sex-ratio) of this species. This study provides the first data on population parameters of P. blennoides in Tunisia. Materials and Methods. Specimens of Phycis blennoides were collected from the landings of the artisanal fisheries between September 2007 and June 2010. The length–weight relations were determined according to the allometric equation: W = aTLb. Growth parameters were estimated using the von Bertalanffy growth equation. Results. Length (TL)–Weight (W) relations were allometrically positive for the females (W = 22.10–4TL3.409), males (W = 13.10–4TL3.674), and both sexes (W = 19.10–4TL3.460), without significant differences between males and females. The relation between otolith weight and age showed a significant difference between males and females. The growth parameters were calculated as TL∞ = 57.17 cm, K = 0.193 · year–1, t0 = –1.578 · year for the females, and 44.74 cm, 0.313 · year–1, and –1.210 · year for the males, respectively. The females grew faster than the males which did not exceed 45 cm. The growth performance index Ф' calculated for the females (2.80 cm· year –1) and males (2.79 cm· year –1) yielded similar results. Conclusion. Results reported in this work will contribute to the knowledge on the biology of P. blennoides in Tunisia, with the aim of generating sufficient information to improve future stock management and sustainable fisheries.