Investigation And Analysis Of Toxic Cyanobacteria Inreservoirs And Fish Ponds Of Nagasaki And Thailand

Aquaculture ponds of catfish and tilapia in North Thailand (2011) and freshwaterreservoirs (Nishiyama dam and Urakami dam) in Nagasaki (2012) were surveyed toobtain the basic information of cyanobacterial toxins and their potential toxin-producers.In this investigation, molecular ecological method was used for detecting cyanobacteriaand the other phytoplankton.In dams, the concentration of chlorophyll-a in Nishiyama dam was remarkably higherthan Urakami dam. TN in Nishiyama dam was lower than Urakami dam. A goodpositive correlation between TN and chlorophyll-a concentration was also found inUrakami dam, whereas no such correlation was observed in Nishiyamadam.In fishponds, the abundance of cyanobacteria in tilapia pond was lower than catfish pond. Theconcentration of chlorophyll-a in tilapia pond was also lower than catfish pond inaverage. TN and TP in catfish pond was higher than those of tilapia pond. This resultshowed that the higher nutrient loading, that is, the dense culture of catfish mightinvolve the higher risk of cyanotoxic,Microcystin, because the toxic species ofcyanobacteria, Microcystis sp., Anabaena sp. and Planktothrix sp. were mainly found incatfish pond.However, these species generally contain toxic strains and non-toxic strains.Therefore, PCR techniques may be an effective method for detecting the toxinproducing genes directly. In this study, genus-specific mcyA gene and PC-IGS genewere quantified by using the real-time PCR method to estimate the population of themicrocystin producing cyanobacteria. The copy number of Microcystis specific16SrDNA gene and cyanobacteria16SrDNA gene were also quantified simultaneously.The concentration of total microcystin and three kinds of analogues of microcystin(MC-RR,-YR,-LR) were analyzed by HPLC. The total microcystin concentration intilapia ponds was lower than catfish ponds. Moreover, the concentration of MC-YRanalogue became numerically dominant throughout the growing season (May to June, 2011) in catfish ponds. The remarkable differences between catfish pond and tilapiapond were found for occurrence of mcy genes and microcystin, which a strongerpositive correlation was observed between MicmcyA，Micpcgenes and microcystinconcentration in catfish pond. But no such strong correlation was found in tilapia pond.The total microcystin concentration in Nishiyama dam was lower than Urakami dam,and only two kinds of microcystin analogues (MC-RR, LR) were identified inNishiyama dam. The concentration of MC-RR analogue became numerically dominantboth in Nishiyama and Urakami dams. The strong positive correlation betweenmcygenes and microcystion concentration was also found in two dams.Some interesting facts were also be found in this study that there were strainspossessing mcy genes but producing no microcystin. One reason of the phenomenamight be that the other mcygene was deleted or broken. The other reason might be thatseveral environmental factors affected the production of microcystin, such as theconcentration of TP and the ratio of TN/TP. Previous studies had showed that the TN/TPratio could affect the mcy gene copy numbers. Moreover, the higher TP concentrationinvolved the higher possibility of occurrence of mcy genes, that is, toxic strains ofcyanobacteria. The study on the cyanobacteria in aquaculture ponds and freshwaterreservoirs in different area can provide valuable information on detecting thecyanobacterial toxins and managing the risk of toxic cyanobacteria to globalenvironment.