Age and Growth of the Grass goby Zosterisessor ophiocephalus Pallas, 1811 in the Gulf of Gabes (Tunisia, Central Mediterranean)

Zosterisessor ophiocephalus is currently an important component of the eastern Mediterranean inshore fisheries. In Tunisia it was recorded for the first time in the Gulf of Gabes in 1993, where it is now an important fished species. In this study age and growth parameters were determined in the Gulf of Gabes (southeast of Tunisia) based on otolith analysis of 824 specimens caught between September 2006 and August 2007. Monthly changes in marginal increments, determined from alternation of macroscopic opaque and translucent bands, of Zosterisessor ophiocephalus sagittae were examined. These results allowed us the estimation of the approximate age to the appearance of each annulus. The observed age was 6 years old for both sexes. Von Bertalanffy parameters based on length at age data were TL infinity = 24.83 +/- 1.69 cm, K = 0.19 +/- 0.03 year(-1) and t(0) = -0.91 +/- 0.12 for males and TL infinity = 24.13 +/- 1.17 cm, K = 0.20 +/- 0.02 year-1 and t(0) = -0.80 +/- 0.09 for females. The length-weight relationship for both sexes of Zosterisessor ophiocephalus is Wt = 0.021 TL (2.789). The size at which 50% of females and males matured was respectively 12.65 cm and 13.91 cm total length (TL). The age at which 50% of females and males matured was respectively 2.9 and 3.5 years.