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The effects of Bacillus probiotic forms on growth performance and microbiota were examined in black tiger shrimp (Penaeus monodon). Shrimp were fed for 120 days with one of three diets; a control diet alone or supplemented with either probiotics consisting of live-sprayed Bacillus (LS) or freeze-dried Bacillus (FD). Culturable bacteria counts in the hepatopancreas, intestine and culture water of the three treatments were relatively constant during the experiment. Bacillus numbers in the hepatopancreas and intestines of probiotic-treated groups increased significantly (P < 0.05) after 30 treatment days and remained relatively constant afterwards while no appreciable changes occurred in the control. Shrimp supplemented with LS and FD contained significantly lower concentrations of Vibrio (P < 0.05) in the hepatopancreas, intestine and culture water, compared to those in the control group. Shrimp treated with LS and FD probiotic bacteria showed a significant improvement (P < 0.05) in specific growth rate (SGR) and feed efficiency (FE), compared to those of control group. Probiotic bacteria have the potential to enhance shrimp culture by reducing Vibrio and improving growth performance. KEY WORDS

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BackgroundMortality episodes have affected young-of-year smallmouth bass (Micropterus dolomieu) in several river systems in Pennsylvania since 2005. A series of laboratory experiments were performed to determine the potential role of largemouth bass virus (Ranavirus, Iridoviridae) in causing these events.ResultsJuvenile smallmouth bass experimentally infected with the largemouth bass virus exhibited internal and external clinical signs and mortality consistent with those observed during die-offs. Microscopically, infected fish developed multifocal necrosis in the mesenteric fat, liver, spleen and kidneys. Fish challenged by immersion also developed severe ulcerative dermatitis and necrotizing myositis and rarely panuveitis and keratitis. Largemouth bass virus-challenged smallmouth bass experienced greater mortality at 28 °C than at 23 or 11 °C. Co-infection with Flavobacterium columnare at 28 °C resulted in significant increase in mortality of smallmouth bass previously infected with largemouth bass virus. Aeromonas salmonicida seems to be very pathogenic to fish at water temperatures < 23 °C. While co-infection of smallmouth bass by both A. salmonicida and largemouth bass virus can be devastating to juvenile smallmouth bass, the optimal temperatures of each pathogen are 7–10 °C apart, making their synergistic effects highly unlikely under field conditions.ConclusionsThe sum of our data generated in this study suggests that largemouth bass virus can be the causative agent of young-of-year smallmouth bass mortality episodes observed at relatively high water temperature.

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