EFFECTS OF FISH CULTURE ON DISSOLVED PHOSPHATASE IN GROUNDWATER

Extracellular phosphatase plays a crucial role in P cycling in aquatic ecosystem. Little attention has been paid on the occurrence of extraccllular phosphatase in groundwater. Furthermore, effects of aquaculture on extracellular phosphatase, especially dissolved alkaline phosphalase,were inadequately studied. The objectivc of this study was to investigate the influences of fish culture on dissolved alkaline phosphatase,including its origin. activity and kinetics,in freshwater. Water was taken from a well,as a control,and 10 different pools rearing a variety of fishes with the same well water in November and December 2001,as well as May 2003,for 5 times. Variables involved in pcycling,such as orthophosphate(o-P)concentrations,size fractionation of alkaline phosphatase. responses of dissolved alkaline phosphatase activity (DAPA)to pH,temperature,CuSO4,ZnSO4,EDTA 2Na. as well as surfactants(CTAB and Triton X-100)and its kinetics,were deternlined. DAPA in groundwater. with and without fish rearing was inhibited by Cu2+ 、CTAB with different concentrations and EDTA-2Na at higher concentration (2mmol/L). At the same time,it was enhanced by Triton X-100 with different concentrations. The sensitive responscs to the spec ificinhibitors provided further evidences that alkaline phosphatase occurred in groundwater. In the water of glass jars with fish culturing,DAPA increased significantly,and the extent of increase was depended on fish species cultured. In details,groundwater with Trichogoster trichopterus and Botia licontei rearing showed significantly higher DAPA than controls. Besides. DAPA was undctectable in the groundwater with Mastcembetus erythrotaenia,Aymphysodon acquifasciata,Monodactylus argentens, Apteronotus aslifrons, Acipenser sinensis Grtey.Cyprinus carpio Linnaeus rearing,but detectable in the water with Gichasoma synspolum,Botia licontei,Mylipharyngodon piceus Richardon,Ctenopharyngodon idellus Cuvier et Valenciennes,Hypophthalmichthys molitrix,Aristichthys nobilis rearin and reshowed the highest value with Trichogoster trichoptern rearing,DAPA was characterized in control and that rearing Trichogoster trichopterus and Botia licontei (culture medium).It showed the highest level at 35℃in control,while it peaked at both 35℃ and 55℃in the culture medium. Its optimum pH was pH 7.0 in control,but was pH 5.8 and pH 8.9 in the culture medium.Moreover,it was enhanced by Zn2+ at higher concentration(0.5mmol/L)in control,but was inhibited significantly by Zn2+ at different concentrations in culture medium.Kinetics of dissolved alkaline phosphatase conformed to the Michaelis Menten model. The significantly higher V max and K m values were recorded in the colture medium compared to those in control.In short,DAPA in culture medium exhibited distinct models responding to temperature,pH ZnSO4 as well as higher V max and K m values. In addition,alkaline phosphatase activity associated with particles(>3.0μm)was very low, or undetectable,coupled with scarcely observed algae cells,indicating that phytoplankton is unlikely to be the main producer of DAPA. Hence the occurrence of DAPA was causatively linked to fish culture. Extracts from particles collected in the bottom of jars with fish culture, by distilled water, exhibited DAPA. It showed a similar manner responding to pH values with that of water in the same jars, implying that the solid wastes resulted from fish culture is one of the sources providing dissolved alkaline phosphatase.