Evidence of Flathead Mullet Mugil cephalus L. Spawning in Waters Northeast of Taiwan

A new spawning ground for flathead mullet (Mugil cephalus L.) in waters northeast (NE) of Taiwan was identified using comparisons of the maturation status of fish to that of well-known spawning grounds in waters southwest (SW) of Taiwan from 20 Nov. 2005 to 12 Jan. 2006. Similarities in hydrographical conditions between the NE and SW waters produced concurrent oceanic fronts with 20-23°C isothermal lines, temperatures which are suitable for mullet spawning in both areas. Mean fork length, body weight, the gonadosomatic index, and gonadal maturation of mullet in the NE waters were all comparable to those in the SW waters in the spawning season around the winter solstice (21 or 22 Dec.)±10 d. The gonadosomatic index of mullet in the NE waters significantly increased from ＜ 0.5 at the beginning of the spawning season to greater than 21.0 for females and 19.0 for males at the peak of the spawning season. Oocytes were all either late-stage vitellogenic or post-vitellogenic from mid-Dec. to mid-Jan. In addition, a few individuals with hydrated oocytes or post-ovulatory follicles were also found. This evidence suggests that waters NE of Taiwan are a suitable spawning ground for the flathead mullet.