Structure de la sagitta, âge et croissance de l’uranoscope (Uranoscopus scaber Linnaeus, 1758) de Tunisie

A hyalin ring, mainly in winter, and an opaque one, mainly in summer, are deposited every year on the sagitta otolith of the uranoscope along the Tunisian coast. The importance of the width of hyalin areas has been accounted for by the fact that otolith grows in a continuous way over the year with the fish, showing organic and mineral deposits in quantities that vary with seasons. This interpretation seems to be original by comparison to the ideas generally admitted in this field. The life span of females (6 years) is longer than that of the males (4 years). A sexual dimorphism can be observed from the third ring as females become larger and heavier than males.Sur la sagitta de l’uranoscope des côtes tunisiennes, se déposent annuellement un anneau hyalin en période hivernale et un anneau opaque en période estivale. L’importance de la largeur des zones hyalines a été expliquée par le fait que l’otolithe croît d’une façon continue tout au long de l’année en même temps que le poisson, avec des dépôts organiques et minéraux en quantité variable selon les saisons. Cette interprétation présente une certaine originalité par rapport aux idées généralement admises dans ce domaine. La longévité des femelles (6 ans) est supérieure à celles des mâles (4 ans). Un dimorphisme sexuel se manifeste à partir du troisième anneau, les femelles deviennent plus grandes et plus lourdes que les mâles.Boundka Bouraoui, Hedi Ktari Mohamed, Quignard Jean-pierre. Structure de la sagitta, âge et croissance de l’uranoscope (Uranoscopus scaber Linnaeus, 1758) de Tunisie. In: Ecologia mediterranea, tome 23 n°3-4, 1997. pp. 65-71

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 (Brünnich, 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