Age and Growth of Phycis Phycis (Linne, 1766) in the Gulf of Tunis

The age of fish in a population is fundamental to most of the questions fishery biologists attempt to answer about that population. The aim of this study was to report the parameters of the weight-length relationship and to estimate the age and growth of Phycis phycis (Linnaeus, 1766) in Gulf of Tunis. A sample of 272 specimens of P. phycis was collected from the landings of the small-scale artisanal fisheries between September 2007 and June 2010. The total length (TL) ranged from 14 to 55.5cm and total weight (TW) from 45 to 1779g. Length-weight relationship were described by allometrically positive for the females (TW = 0.0083*TL3. 0703), males (TW= 0.0063*TL3.1471), and both sexes (TW= 0.0082*TL3. 0759). No significant differences were found between males and females (ANCOVA, p = 0.426). Symmetry between the right and left otolith was compared. The relation between the total length (TL) of fish and the weight of the otolith (Wo) did not show a significant difference between the right (Wo = 0.12 TL – 0.163) and left otolith (Wo = 0.11 TL – 0.124) (ANCOVA, p 0.05). The relationships between otolith radius and otolith weight with age, showed that there are no significant differences between males and females (ANCOVA, p 0.05). The growth parameters for females (TL = 73.43 (1 - e-0.158 (t+1.709))), males (TL = 67.51 (1 - e-0.168 (t+1. 993))) and combined sexes (TL = 65.73 (1 - e-0. 135 (t+2. 025))) were estimated. The females, reaching L∞ = 73.43 cm, grew faster than the males, which did not exceed 68 cm. Moreover, the females have the higher predicted asymptotic weight (W∞= 4446.08g) compared to the males (W∞= 3603.20g).Consequently, the index of performance from growth (Ф) (cm/an) of the females (Ф=2.929) was higher than the one of the males (Ф=2.883). Age estimation in gadiform fish has been known to present some difficulties due to otolith thickness, which in most species requires special processing methods so that growth increments become visible.