Bacteria variation in Litopenaeus vannamei high level ponds and its relation with physical-chemical factors

From April to August, 2008, we had collected water sample in high level ponds of Litopenaeus vannamei at Honghai Bay, Shanwei, Guangdong to study its significant bacterial population and physical-chemical factors, and to analyze the variation of bacterial population and its relation with environmental factors during the culture period. The results show that the amounts of heterotrophic bacteria, Vibrio and Bacillus in water change rather greatly. Specifically, the heterotrophic bacteria range from 1.35×10⁴ cfu · mL^-1 to 1.39×10⁶ cfu · mL^-1, 4.73×10⁵ cfu · mL^-1 on average; as for Vibrio, the range is 1.05×10³~5.20×10⁴ cfu · mL^-1, 1.80×10⁴ cfu · mL^-1 on average; and for Bacillus, the range is 0.11×10³~4.30×10³ cfu · mL^-1, 6.6×10² cfu · mL^-1 on average; the amount of fecal coliform is generally less than 1.0×10² cfu · L^-1 with an average of 0.97×10² cfu · L^-1, which is much below the standard for pollution-free food and aquaculture water quality. Additionally, the correlation analysis between bacteria amount and physical-chemical factors reveals that the heterotrophic bacteria amount and DO show a significant negative correlation (P<0.05), while Vibrio amount shows a very significant negative correlation with pH (P<0.01)but a significant positive correlation with COD and TP (P<0.05).The multi-factor partial correlation analysis reveals that the correlation between heterotrophic bacteria and Vibrio, DO, pH, COD, TP is not significant (P>0.05).To sum up, L.vannamei grows well in the investigated ponds, which is proved a safe and relatively healthy system, and the bacteria amount in water environment is affected and restricted by biological, environmental and artificial factors.