The study of annual cycle of gonads developments and sex steroids of gray mullet, Mugil cephalus in Golestan Province

Grey mullet, Mugil cephalus is one of the most famous and valuable fish on the fisheries and aquaculture industry. This species is the most suitable to introducing the southern, northern and central regions of our country due to high resistant to large variation of water salinity and temperature. On the monthly sampling period biometric data including total length and total weight recorded and length and weight classes for every sex were determined. To understanding of physiological functions and sexual development of reproductive organs, this investigation carried out with Grey mullet imported from Hong Kong by 1993. Findings of this research can be used for management of artificial breeding of this species. Daily variation of pond water temperature was recorded. Sex steroid hormones and other plasma metabolites such as Ca^2+, cholesterol, triglycerides and total proteins were measured by blood sampling. Gonad samples were prepared in order to histological studies. Oocyte growth was studied by measurement of egg diameters. Measured values of cholesterol, triglycerides of blood plasma revealed that these metabolites have seasonal variation and severely deposited on the summer and mobilized on the spawning seasons. Findings of this research suggested that egg diameters, values of sex steroid hormones (estradiol and progesterone) and Calcium concentrations of fish blood plasma shortening increased a long with day length shortening