Annual reproductive cycle, spawning periodicity and sexual maturity of false scad Caranx rhonchus (Geoffroy Saint-Hilaire, 1817) (Pisces, Carangidae) from the South-Eastern Mediterranean (Gulf of Gabès, Tunisia)

Abstract

Summary The reproductive biology of Caranx rhonchus (Geoffroy Saint-Hilaire, 1817) (Pisces, Carangidae) was studied in the Gulf of Gabes (Mediterranean Sea) from June 2004 to May 2006. Of 1313 individuals examined, 668 were females (50.9%) and 645 were males (49.1%). The overall sex ratio did not deviate significantly in favour of females (♀ : ♂ = 1.04 : 1). Monthly changes in the Gonado–Somatic Index (GSI) showed a rapid increase from May to June and an extended very high level from June to September (4.43–3.47% for females and 3.35–2.61% for males), before declining sharply in October (down to 2.02% for females and 0.57% for males). The gametogenesis activity began with a pre-maturation phase from March to May, followed by a ripe-spawning phase from June to September. From the last days of July to the end of October, the gonads were in the spent and post-spawning stages. From November to early May, gonads were in the resting stages. The size at which 50% of the population reached sexual maturity was not significantly different between males and females : males attained sexual maturity at fork length FL50 = 161.20 ± 0.37 mm (n = 262), whereas females attained maturity at FL50 = 160.70 ± 0.23 mm (n = 296). The age of maturity for both sexes occurred at 2.1 years.