Large Yellow Croaker Precocious Endocrine Mechanism

Using histological staining methods, SABC immunocytochemical technique and electron microscope technique, the difference of the encephalon, the pituitary and the gonad in precocious and unprecocious large yellow croakers are compared. The results indicated:1 .There is obvious difference between the gonads of precocious and unprecocious fish: in female, the ovaries of unprecocious fish stay in 141 stage, and are mainly consisted of oogonias and early oocytes; the ovaries of precocious fish have developed into IIIAV stage, most of the oocytes are in the large growth stage. In male, the testis of the unprecocious fish stay in 11桰ll stage, most cells in testis are spem~atogonium, primary spermatocyte, secondary spennatocyte and a few spermatozoon. The testis of precocious fish have developed into 1V-V stage, and are mainly consisted of spennatid and lots of spermatogonium. The ultrastructure of the interstitial cells in precocious fish indicate that the cells have developed into maturation and are in their secretive period, but those in unprecocious fish not.2.GnR.H immunocreactive(ir) cell bodies exist in transitional areas between the olfactory nerve and the olfactory bulb, the ventral olfactory bulb, the ventral telencephalon, NPO and NLT of the hypothalamus. GnRH-ir fibers distribute in the various brain region from the olfactory bulb to the cerebellum. They are especially abundant in the hypothalamus, the preoptic area and the ventral telecephalon. The immunopositive reaction in precocious fish is evidently stronger than that in unprecocious fish, and there is only very weak reaction in the gonadal undeveloped fish. The differences are most obvious in the hypothalamus, but not in other areas.3.The gonadotrops mainly exist in the rostral pars distalis(RPD) and the proximal pars distalis(PPD) of the adenohypophysis, a few extend to the top of ventral PPD and the edge of the pars inteimedia(PI). The gonadotrops in the PT always appear in the gonadal mature fishes. The area that the gonadotrops exist enlarge in the pituitary of the30precocious fishes, extend from PPD to RPD and P1. The volume of the gonadotrops increase l/2,the secretive granule and mcuoled cells also increase in number. GnRH receptor exist in the cytomembrane of the gonadotrop~. The inimunopositive reaction and the distributive area are stronger and larger in precocious fishes.All above founding demonstrated for the first time that the precocity of the large yellow croaker has a relation with its reproductive endocrine mediatoiy axis. The secretive increasing of (JnRH in the hypothalamus and GTH in the pituitary may have a effect related to earlier gonadol maturation. The founding can provide academic gist for scientific prevention and effective resolvement for the problem of earlier gonadol maturation.