The result of enclosure experiment carried out from summer to autumn in 1995 and 1996 .It showed that during feeding period the gross primary production of phytoplankton (PPGP)was lower and respiration of water column (WR)relatively higher , in most enclosures PPGP/WR <1 , the PPGP in enclosures polycultured shrimps and a hybrid tilapia was higher , in opposite , the enclosure polycultured shrimps , tilapia and Ruditapes Philippinarum had the lowest PPGP.When suitable fertilization was adopted on the basis of daily feeding , PPGP in experimental enclosures was significantly higher than that as only feeding was adopted , PPGP/WR >1 , but there was not apparent difference in PPGP between enclosure monocultured shrimps , polycultured shrimps and tilapia , polycultured shrimps and bay scallop , and polycultured shrimps and Sinonvacula constricta .These results indicate that the cultural management measures , routine feeding and fertilization , stocked tilapia and bivalve and periphery algae all affect the gross primary production in enclosures , in which management measures usually play an important role .