Reproductive biology of purpleback flying squid (Symplectoteuthis oualaniensis) in the south-central South China Sea in spring and autumn

We studied the reproductive biology of Sthenoteuthis oualaniensis in the south-central South China Sea using a total of 4 016 specimens collected in September 2012 and March 2013. The sex ratio of S.oualaniensis was about1:1. The proportion of StageⅠand StageⅡ was higher in spring, while that of StageⅡ and StageⅢ was higher in autumn. Gonad somatic index (GSI) was higher in autumn and male. For mature female, when mantle length was less than 141 mm or more than 150 mm, GSI increased with increasing mantle length. The highest GSI was 9.71 when the mantle length was 121～140 mm. The individual absolute fecundity was 63～97 074 eggs and 24～60 378 eggs, the average was 8 635 eggs and 10 234 eggs in spring and autumn, respectively. The fecundity was stronger than that in autumn. The individual absolute fecundity was positively correlated with mantle length, body weight and net body weight very significantly (P0. 01) . The mature egg diameter distribution range was 400～1 200 mwith an average of (769 261) m. The results indicate that the reproductive strategy characteristics of S.oualaniensis were small eggs, asynchronous mature,batch spawning and high fecundity.