20 MARCH 2017 • WORLD AQUACULTURE • WWW.WAS.ORG the surface of eggs or the GIT by producing antimicrobial compounds or by outcompeting them for nutrients or mucosal space (Bandyopadhyay and Mohapatra 2009). Certain pathogens produce proteolytic enzymes that can dissolve and digest the bacteria that approaches them, the most remarkable being Streptococcus and Bacillus pyocyaneus (Rettger 1905). Many studies have addressed the use of probiotics in aquaculture, such as the improvement of the survival of portunid crab larvae Portunus trituberculatus through the application of probiotic Thalassobacter utilis in the rearing water (Nogami and Maeda 1992, Nogami et al. 1997). Lactic acid bacteria, notably Lactobacillus sp., Bifidobacterium sp. and Streptococcus sp. are effective against diseases caused by Vibrio sp. (Gatesoupe 1994, Olsson et al. 1998). Bacillus subtilis BT23 has inhibitory effects against vibriosis in tiger shrimp Penaeus monodon (Vaseeharan and Ramasamy 2003). Application of a Bacillus strain to the common snook Centropomus undecimalis increased larval survival, promoted better growth and decreased the number of suspected pathogenic bacteria in the fish gut (Kennedy et al. 1998). Alteromonas sp. can reduce the infection of Vibrio sp. in Pacific oyster Crassostrea gigas larviculture (Douillet and Langdon 1994). Some Pseudomonas fluorescens strains reduce the mortality of rainbow trout Oncorhynchus mykiss fingerlings infected with a pathogenic V. anguillarum (Gram et al. 1999). FIGURE 3. Antagonistic effect of potential probiotic exhibited the inhibitory ability on the growth of pathogenic bacteria (LEFT). No inhibition of pathogen found on non-probiotic isolate (RIGHT). Photos: Loh J.Y. FIGURE 2. (LEFT) Purified PCR products for 16S rRNA gene sequencing and identification. (RIGHT) Pure culture of probiotic in lyophilized form. Photos: Loh J.Y.
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