A mass mortality of farmed juvenile abalones (Haliotis discus hannai) occurred in South China in December of 2012. Combined traditional culturing with terminal restriction fragment length polymorphism (T-RFLP) methods, microbial communities associated with juvenile abalones were investigated under different survival conditions, including healthy (HA) and moribund (HM) abalones in the healthy pond with low mortalities, and healthy (DA) and moribund (DM) abalones in the diseased pond with a high mortality rate. The results indicated that both HA and DM exhibited greater microbial diversity and evenness. Moreover, the number of bacterial colony forming units (CFUs) from HA and DM were higher than other samples from the same pond. HA and DA samples harboured absolutely dominant T-RFs with 504bp (76.2 of total T-RFs) and 436bp (63.2) respectively. Nesterenkonia sandarakina, Staphylococcus haemolyticus and Agarivorans albus were the dominate isolates in HA samples, but no Vibrio genus was isolated even on vibrio-specific medium. Reversely, in the DM samples, up to 94 of the total bacterial CFUs were composed of the family Vibrionaceae, represented by Photobacterium swingsii (44) and Vibrio shilonii (45). Also, Vibrio was the only cultivated genus from the HM group. Of these Vibrio species, V.atlanticus were detected in HM, DA and DM samples and could generate the T-RF 504bp. The microbial composition and diversity of juvenile abalones in different surviving states provided insights into the stability and dynamics of microbial communities during disease outbreak which could be helpful to predict and to control disease in the future.
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