Abstract:The main biological characteristics, the main spawning period and fecundity characteristics of jack mackerel spawning stock were studied based on the sample data obtained in Diaoyu Islands waters in March, 2005. The results showed that the Diaoyu Islands waters was the main jack mackerel spawning grounds in the southern East China Sea in spring, and the main spawning period was in the middle and late March. According to the fork length and weight frequency distribution, the main spawning stock had three dominant folk length groups, 200~220mm, 230~240mm, and few individuals of 260~270mm. The composition characteristics of body weight were consistent with the fork length composition. Since the samples were taken in the late spawning period, the conditional growth factor was relatively small. The absolute individual fecundity was 12 264±37 629 grain and the mean individual absolute fecundity was 27 844±10 179 grain. The fecundity per unit length was in the range of 50~157 grain/mm, at an average of 121±42 grain/mm. The fecundity per unit net weight was in the range of 82~238 grain/g,at an average of 202±68 grain/g.
