Change of dominant species of planktonic microalgae in Litopenaeus vannamei's semi-intensive culture ponds and its impact on the culture environment

Investigations on the microalgae community were conducted in Litopenaeus vannamei's semi-intensive culture ponds.The variation about dominant species of microalgae in shrimp ponds were identified,moreover,their relationships with culture environment and culture efficiency were analysised.The results showed that a total of 16 dominant species of microalgae were identified.The dominant species in initial phase were Chlorella pyrenoidosa,Nitzschia closteriu and Peridinium pusillum;the ones in the mid-phase were Cyclotella operculata,Lyngbya gardnari,Oscillatoria chlorine,K.microscopica Nygaard,C.kessleri,Cylindrospermum muscicola,C.kuetzingiana,O.salina,Chroococcus cohaerens and O.willei;the ones in the final phase were O.neglecta,O.angustissima and C.pyrenoidosa.Microalgae in initial phase were rare and low density,but Dinophyta occupied the dominant position in pond 2 and pond 4,which caused the low survival rate of their shrimp.The succession of Microalgae in the mid-phase was more frequent by weather interference.But due to undesirable algae in pond 1 and pond 2,their resistance to severe weather was weaker than the one in pond 3 andpond 4.In the final phase,the dominant species'number reduced and their dominance was prominent,and Oscillatoria bloom well,but theshrimp in pond 1 fell sick.The result showed that the algae composed by excellent dominant species could play a positive role in stabili-zing the environment,and effectively resisted the interference by the weather interference,eventually.The shrimp grow health and cultureefficiency was good.However,the algae composed by the undesirable microalgae could bring stress to the shrimp growth,increased the riskof culture,and reduced the culture efficiency.