Annual reproductive cycle, spawning periodicity and sexual maturity of blue runner C aranx crysos ( P isces, C arangidae) from the G ulf of G abes ( T unisia, E astern M editerranean)

Summary From J une 2004 to M ay 2006, the reproductive biology of the blue runner C aranx crysos was studied in the G ulf of G abes ( S outhern T unisia). Of 1668 individuals examined, 777 were females (46.6%) and 891 were males (53.4%). The sex ratio significantly deviated in favour of males (♀:♂ = 0.87 : 1). The difference in the numbers of females and males was significant among size‐classes. However, there was no significant difference between sexes over months and seasons. Monthly changes in the G onado‐ S omatic I ndex ( GSI ) showed a rapid increase during summer to very high levels in July (3.51% for males and 2.55% for females) and A ugust (3.47% for males and 2.59% for females) before declining sharply in S eptember (0.58% for females and 0.38% for males). The gametogenesis activity began with a pre‐maturation phase, from 20 M ay to the first 10 days of J uly, followed by a pre‐spawning phase, from 20 J uly to 20 A ugust. From the last 10 days of A ugust to 20 S eptember the gonads were in the ripe and spawning stages. From the end of S eptember to early M ay, gonads were in the post‐spawning and resting stages. The size at which 50% of the population reached sexual maturity was significantly different in males and females: males attained sexual maturity at fork length FL 50  = 210.20, whereas females attained maturity at FL 50  = 222.3 mm. Age at maturity was 2.4 years for males and 2.8 years for females.