The pathogens from ill turtles, eels and Ictiobus cytrinellus were separated, purified and identif ied to prove up the biocontrol function of Photosynthetic bacteria ( PSB ) on diseases of aquatic animals. The pathogenicity of pathogens is examined by artificially infecting the healthy animals. And the antibacterial abilities of sal-t resistant Rhodospirillaceae bacteria against those separated pathogens were studied. At the same time, the phases that PSB produces ef fective antibacterial action were determined. The results show that the separated pathogens from aquatic animals are Vibrio , Aeromonas, and Pseudomonas. The metabolic products of sal-t resistant Rhodospirillaceae bacteria show the bacteriostastic activity to those separated pathogens: the diameter of ant ibacterial zone is 1. 2- 1. 4cm, the minimal inhibitory concentrat ions ( MIC) are mostly at the diluted times 4 - 8. The antagonistic substances of sal-t resistant Rhodospirillaceae bacteria are produced in the exponential phase initially and reached maximal concentration in the contabescence phase.