Outbreaks of serious mortality among cultured abalone postlarvae have occurred across Southern China since July 2002. Five motile bacterial strains were isolated from diseased abalone postlarvae on tryptic soy agar supplemented with 1% NaCl (TSA1) and/ or thiosulphate citrate bile salt (TCBS) sucrose agar plates during an outbreak in August 2003 in Shanwei, Guangdong province. All isolates were characterized and identi¢ed asVibrio alginolyticus on the basis of biochemical characteristics and comparisons with those of the reference strainV. alginolyticus ATCC 17749. Strain 19 (a representative of ¢ve similar isolates) was virulent to abalone postlarvae with an LD 50 value of 1.00 Â 10 4 colony-forming units mL À1 . All abalone postlarvae exhibited the same signs as in natural outbreaks. The same bacterium could be re-isolated from abalone postlarvae after bacterial challenge using TSA1and TCBS plates. The results reveal thatV. alginolyticus is an infectious agent of abalone postlarvae.

Mass mortality among the post-larvae of cultured abalone Haliotis diversicolor supertexta has occurred on the south coast of China since 2002. The diseased abalone are generally 10 to 30 days old, and typical signs of the disease include them turning white in colour and falling off the diatom films on which they were cultured. Among sixteen different motile bacteria isolated from the diseased post-larvae, four were identified as Vibrio parahaemolyticus on the basis of biochemical characteristics when compared with those of a V. parahaemolyticus type strain ATCC 17802(T). Isolate 25, a representative isolate of V. parahaemolyticus recovered from diseased abalone, was virulent for the post-larvae with an LD(50) value of 3.5 x 10(5) CFU (colony forming units)/ml. All moribund post-larvae artificially infected with the bacterium turned white and fell off the diatom films on which they were cultured as seen to occur during natural outbreaks of the disease, and it was possible to recover the bacterium from artificially infected post-larvae. The results of the study indicate that V. parahaemolyticus is a pathogenic bacterium to abalone post-larvae.

White shrimp, Litopenaeus vannamei, is a widely farmed species. In China, shrimp postlarvae (PL) are frequently subjected to salinity reduction treatment to meet end growers' needs. However, although this treatment effectively reduces vibrio counts, its impact on gut microbiota health is still unknown. In this study, we applied a euryhaline strain of BALOs, BDN-1F2 (BD), and Bacillus subtilis (SD) to the rearing of secondgeneration shrimp PL after salinity reduction treatment so as to determine if they could impact PL gut microbiota by using high-throughput sequencing analysis. Results show that PL gut microbiota, both compositionally and functionally, have been badly wrecked after salinity reduction treatment with the generally recognized as opportunistic pathogens Gammaproteobacteria being the only dominant class at day 1 of test, viz., 99.43, 85.61, and 83.28% in BD, SD, and control (CD) groups, respectively. At day 7, Gammaproteobacteria was still the only dominant class in the SD and CD groups with relative abundance of 99.77 and 99.87% correspondingly, whereas in the BD group, its value dropped to 8.44%. Regarding biodiversity parameter the Shannon index, over the 7-day test period, while the SD group was unchanged (0.98-0.93), the CD group dropped to 0.94 from 2.94, and the BD group was raised to 7.14 from 0.93. Functionally, compared to control, the SD group displayed similar strength of various predicted community functions, but the BD group had hugely enhanced its various capabilities (p < 0.05). These results demonstrated that the addition of BDN-1F2 had exceedingly improved PL gut microbiota health by raising its biodiversities and strengthening its functionalities. On reviewing data derived from this as well as relevant studies, a Shannon index cutoff value was tentatively suggested so as to differentiate microbiota-healthy PL7-15 from the unhealthy ones. Furthermore, a conceptual mechanism of BALOs in the rectification/improvement of the microbial community health has also been proposed.