| Summary: | Chapter 2: Bacterial pathogens are a leading cause of disease in hatchery aquaculture systems and preventative methods such as probiotics as feed supplements and water additives is well documented. However, comparisons between the effectiveness of using probiotic water additives over traditional biocontrol methods are less understood. This study assessed the effects of ultraviolet irradiation (UV), ozonation and Bacillus spp. as a water additive (probiotic), in the culture of European lobster in a semi-closed recirculation system. Stage I larvae were assigned to one of six treatment groups consisting of 1) ozone, 2) probiotic, 3) probiotic + ozone, 4) probiotic + ozone + UV, 5) ozone + UV, or 6) probiotic + UV, for 18 days. Growth and survival at stages I-V were measured on 1, 6, 11, 18, 24, 31 days post hatch and 1, 18, 24 and 31 days post hatch respectively. Bacterial counts of pathogenic Vibrio spp. in culture water were measured at 1, 4, 9, 14, 18 days post hatch. Lobsters were also exposed to a physiological fitness test (low salinity challenge) at megalopa stage IV, 7 days post treatment. Ozone was comparatively more beneficial than probiotic with increased live weight gain in the ozone treatment over probiotic between zoea stage IV-V (>5 mg). Survival rates were higher in the ozone treatment than probiotic on days 18, 24, and 31 (~66, ~117 and ~120%, respectively). There was a greater biomass in the ozone treatment than probiotic on days 18 and 31 respectively (~60 and ~116%, respectively). Total Vibrio spp. present in the ozone treatment was 99% less than in the probiotic treated culture water (day 18). Results between UV treatment groups showed significantly lower numbers of Vibrio spp. present in probiotic + ozone + UV culture water 4 days post hatch than ozone + UV (~10 fold higher) or UV + probiotic (~15 fold higher) and by day 18 probiotic + ozone + UV was significantly higher than ozone +UV (~8 fold higher). Osmoregulatory challenge test resulted in no significant differences in physiological ...
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