Seasonal changes in ovarian activity of New Zealand turbot (Colistium nudipinnis) and brill (C-guntheri)

Seasonal changes in ovarian activity were investigated in New Zealand turbo t Colistium nudipinnis (Waite 1910) and brill Colistium guntheri (Hutton 18 73), collected by commercial trawlers along the west coast of the South Isl and of New Zealand. Both species demonstrated group synchronous oocyte deve lopment, with a capacity for multiple ovulations within a reproductive seas on. During a 17-h trawl survey, ovulated turbot were caught between 1500 an d 2030 h, indicating a daily spawning rhythm. The turbot and brill spawning seasons were prolonged (late autumn to mid summer). A protracted spawning season confers some advantages in aquaculture.