Reproductive biology and sexual maturity of female jack mackerel, Trachurus declivis (Jenyns), in eastern Tasmanian waters

Abstract

The reproductive biology of female jack mackerel, Trachurus declivis, was determined from fish sampled from November to March, 1987 to 1991, from commercial purse-seine catches and research trawling. Histological, microscopic and macroscopic techniques were used to examine the ovaries of T. declivis. Half of the female fish were sexually mature (Stage 3) at 31.5 cm fork length, and all fish were mature by 37.0 cm fork length. Oocyte development and pre-ovulatory atresia were similar to those of other species of the same genus. The size-frequency distribution of oocyte diameter was polymodal, indicating serial spawning. Atresia was present in all oocyte stages studied, with its occurrence increasing with increasing stage of development. Despite sampling during the spawning season, post-ovulatory follicles were not found, possibly owing to rapid reabsorption or to spawning fish not being vulnerable to the sampling gear.