Comparison on phytoplankton community structures in three pond polyculture modes with Ctenopharyngodon idellusas dominant stocking species

During June to October,2010,phytoplankton community structures were compared in three pond polyculture modes with Ctenopharyngodon idellus as dominant stocking species(ModeⅠ,250 C.idellus,35 Hypophthalmichthys molitrix,40 Aristichthys nobilis and 15 Carassius auratus;ModeⅡ,250 C.idellus,35 H.molitrix,20 A.nobilis,20 Polyodon spathula and 15 C.auratus;model Ⅲ,250 C.idellus,35 H.molitrix,and 15 C.auratus).These experiments were carried out in land-based fish ponds,which located at aquaculture base of Shaotanhe Reservoir,Wuhan city,Hubei province.According to the result,the phytoplankton assemblage was composed of 279 species in total,belonging to 118 genera,8 phyla which were Cyanophyta(29 species,20 genera),Chlorophyta(137 species,63 genera),Bacillariophyta(59 species,20 genera),Euglenophyta(45 species,7 genera),Chrysophyta(3 species,3 genera),Cryptophyta(3 species,2 genera),Xanthophyta(2 species,2 genera),and Pyrrophyta(1 species,1 genera).The phytoplankton density averaged 7.66×107 ind./L,6.95×107 ind./L and 6.74×107 ind./L,respectively.The phytoplankton biomass averaged 70.71 mg/L,62.12 mg/L and 85.52 mg/L,respectively.Comparing the phytoplankton community diversity in three culture modes,we found that the Shannon-Wiener diversity index and Pielou evenness index of phytoplankton community in Mode Ⅱ increased gradually as culture time went on,and the highest level appeared in September in all the three modes.The results showed that the phytoplankton community of Mode Ⅱ was more stable and in a better development state.