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Abstract
Juvenile western king prawn P. latisulcatus were fed 105 colony-forming units (CFU)/mL of two probiotics Pseudomonas synxantha and P. aeruginosa for 28 days. P. latisulcatus were then challenged with V. harveyi at 0 (control), 103, 105, and 107 CFU/mL. During the seven days of challenge, disease resistance of the probiotic-fed prawns was compared with that of prawns not fed probiotics. The immunological responses of the prawns did not improve during the challenge period in terms of total haemocyte count, hyalinocyte, semi-ganulocyte, granulocyte, clotting time, bacteraemia, and intestinal bacterial load. Overall, when prawns were challenged with V. harveyi, the LT50 values got shorter as V. harveyi concentration increased. LT50 values of prawns fed probiotics were significantly longer (P < 0.05) than those not fed probiotics. At a V. harveyi concentration of 103 CFU/mL, the 100% survival of the prawns fed probiotics was three times more likely than those of the prawns not fed probiotics.
This study was supported by the AusAID scholarship for the first author. The authors wish to thank Simon Longbottom for system design of the trials and Lam V. Tai for laboratory work. The authors also would like to thank Nguyen D. Thuan, Nguyen V. Tuan, Nguyen N. Thao, and Le V. Khoi for help collecting the prawns. Sincere thanks are given to the Animal Health Laboratory for kindly providing V. harveyi. Special thanks are due to Rob Lovell for proofreading the manuscript.