Comparison of species composition of phytoplankton and heterotrophic bacteria number between normal shrimp culturing ponds and disease-occurred ponds

The species composition of phytoplankton and heterotrophic bacteria number in the normal shrimp culturing ponds were compared to those in the disease-occurred ponds by trawling method and spread plate method.The results showed that 40 species of phytoplankton in 31 genera were observed,which belonged to Bacillariophyta,Chlorophyta,Cyanophyta,Pyrrophyta,Euglenophyta, Cryptophyta and Xanthophyta;however,only Scenedesmus dimorphus(Turp.) Kutz.and Oscillatoria sp.were observed in the four studied ponds.There were more phytoplankton classes and species in the normal shrimp culturing ponds than the diseased-occurred ponds.The abundances of Cyanophyta species were 6.16%and 9.77%respectively in the two normal shrimp culturing ponds and lower than those in the two disease-occurred ponds(18.85%and 43.38%),while the diversity and evenness indexes of phytoplankton in the two normal shrimp culturing ponds were higher.The similarities of phytoplankton community between different ponds were not related to the occurrence of diseases.The total number of heterotrophic bacteria in the disease-occurred ponds was higher than that in the normal shrimp culturing ponds.