The effects of temperature and photoperiod on ovarian development in captive grey mullet (Mugil cephalus L)

A series of sixteen environmental experiments, conducted under controlled laboratory conditions during the refractory period in the reproductive cycle of the grey mullet, determined the effect of photoperiod and temperature on the vitellogenesis of intraovarian oocytes. Fish subjected to the natural light cycle and ambient water temperatures (24–26°C) served as controls. A classification of stages of vitellogenesis (I–V) is used to determine the percentage composition of oocytes for each fish at intervals throughout the experiment following sampling in vivo.Onset of vitellogenesis is timed by the environmental conditions. A retarded photoperiod, irrespective of preconditioning photoperiod, plays a dominant role in stimulating oocyte growth. Temperature regulates vitellogenesis towards functional maturity. The combination of retarded photoperiod (6L/18D) and constant temperature of 21°C is the most effective for the completion of vitellogenesis of oocytes to functional maturity.Regular injections of pregnant mare's serum gonadotropin (PMSG) at 1 IU/g body weight are effective in initiating vitellogenesis.