Selection of Vibrio harveyi-resistant Litopenaeus vannamei via a three-round challenge selection with a pathogenic strain of V. harveyi

• A novel three-round selection procedure for selection of resistant shrimp.
• The cumulative mortality of shrimp decreased by 66.6% after selection.
• The hours of beginning death of shrimp prolonged by 4 h after selection.
• The hours of ending death of shrimp prolonged by 14 h after selection.
• The LD50 of 96 h of shrimp increased by 9.4 times after selection.

To obtain Vibrio harveyi-resistant Litopenaeus vannamei shrimp used for study on immune response of shrimp avoid vibriosis, a three-round challenge selection procedure was applied. In this procedure, resistant shrimp were selected gradually via three rounds challenge experiment with a pathogenic strain of V. harveyi at a median and controllable lethal dose of 96-h LD50 (the median lethal dose). After this procedure, the cumulative mortality of selected shrimp during 96 h after injection of V. harveyi at 2.0 × 106 cfu shrimp−1 significantly decreased from 93.3% to 26.7%, the hours of beginning of death and the hours of attaining of the maximum cumulative mortality of shrimp prolonged from 4 h and 10 h to 8 h and 24 h, respectively. The LD50 of 6 h, 12 h, 24 h, 48 h and 96 h of selected shrimp significantly increased to 1.4 ± 0.1 × 107 (p < 0.01), 5.5 ± 0.4 × 106 (p < 0.01), 3.1 ± 0.2 × 106 (p < 0.01), 2.7 ± 0.1 × 106 (p < 0.01) and 2.7 ± 0.1 × 106 cfu shrimp−1 (p < 0.01), about 15.9, 15.3, 9.4, 10.0 and 10.4 times of that of normal shrimp, respectively. In conclusion, the resistance of shrimp to Vibrio significantly increased after the three-round challenge selection procedure.