I have a few references on this topic, although they are a bit dated:
Kuo, C.M.
1995. Manipulation of ovarian development and spawning in grey mullet, Mugil cephalus L. Israel. J. Aquacult. Bamidgeh 47(2):43-58.
Kuo, C.M., C.E. Nash, and Z.H. Shehadeh.
1974. A procedural guide to induce spawning in grey mullet (Mugil cephalus L.). Aquaculture 3(1974):1-14.
Pien, P.C. and J.C. Liao.
1975. Preliminary report of histological studies on the grey mullet gonad related to hormone treatment. Aquaculture 5, 31-39.
Shehadeh, Z.H., C.M. Kuo, and K.K. Milisen.
1973a. Validation of an in vivo method for monitoring ovarian development in the grey mullet (Mugil cephalus L.). J. Fish Biol. 1973(5):489-496.
Shehadeh, Z.H., W.D. Madden, and T.P. Dohl.
1973b. The effect of exogenous hormone treatment on spermiation and vitellogenesis in the grey mullet, Mugil cephalus L. J. Fish Biol. 1973(5):479-487.
Tamaru, C.S., C.S. Lee, C.D. Kelley, G. Miyamoto, and A. Moriwake.
1994. Oocyte growth in the Striped mullet, Mugil cephalus L., at different salinities. J. World Aquacult. Soc. 25, 109-115.