Inhibin and activin are disulphide-linked dimeric proteins that belong to the transforming growth factor superfamily. Inhibin and activin are identified that they have ability to modulate the secretion of follicle-stimulating hormone, FSH, from pituitary. Activin can stimulate FSH secretion, on the other hand, inhibin can inhibit FSH production. According to many researches, inhibin and activin play an important roles in regulation of reproduction. Black porgy (Acanthopagrus schlegeli) is belong to protandry.that has a complex regulation in sex differentiation and development. The male differentiation in black porgy started at fourth month, and the testis become mature when the spawing season coming.in the first two year in black porgy, they are differentiate to functional males, and some of them will change to females in the third year. The objectives were to study the possible roles of inhibin¡Bactivin subunits and their receptors in sex differentiation and sex change in black porgy. The gene expression of activin system increase during the period of ovarian development. The expression of activin receptors in ovarian tissue are higher than in testis tissue in the testis-excision experiment. The expression of inhbab ¡Bacvr1and acvr2b after testis-excision are higher than in control in black porgy forebrain. The expression of inhbaa increase at four to five months after hatching in 0+-yr old black porgy, and the expression of inhbb and receptors decrease at the same time. According to these results, activin system may involve in the ovarian development and mature, and play important roles in testis differentiation and development in black porgy. Furthermore, activin system have sex dimorphisms in forebrain in black porgy.

The present study used Escherichia coli¡]BL21¡^that contained pET-23a-bpGH plasmids, to express black porgy growth hormone ¡]bpGH¡^. The bpGH was refolded at pH 11.3 in the presence of catalytic amounts of cysteine and purified by ion exchanger chromatography and gel filtration chromatography. The purified bpGH is a monomer and has a molecular weight of 22 kDa. Using the bpGH, the effects of the growth hormone on growth, essential amino acid deposition and nonspecific immunity in black porgy were studied. The experiment was a 4*3 ¡]diet*GH¡^ factorial design. Four experimental diets were formulated in that fish meal was replaced by the mixture of soya protein and gelatin so that fish meal / soya mixture = 100 / 0, 75 / 25, 50 / 50 and 25 / 75, respectively. GH treatments included non-injection, once per 3 days and once per 12 days. GH was injected intramuscularly at a dosage of 0.05 µg / g wet body weight. The growth trial lasted for 72 days. The results showed that GH administration significantly enhanced weight gain, feed efficiency, protein efficiency ratio and muscle methionine concentration of the fish. GH injection improved the growth performance of the fish fed low protein quality diets to a level equals to the groups fed high protein quality diets. These results indicate that GH injections enhanced the perferential absorption and deposition of the first limiting amino acid methionine from the diets. In addition, GH administration enhanced alternative complement activity and increased serum lysozyme concentration, implicating the enhancement of the immunity.