Acute hepatopancreatic necrosis disease (AHPND), caused by Vibrio parahaemolyticus carrying plasmid-borne binary toxin gene, is one of the leading causes of losses in shrimp aquaculture. There are no commercially available therapeutics to control AHPND, but AHPND-tolerant lines have been reported. This suggests that genomic selection could be employed to develop AHPND-resistant lines. We used a genomic selection program to develop AHPND-resistant lines of Penaeus vannamei shrimp using a single-step GBLUP approach, using data collected from two experimental challenges involving family lines that differed in their growth performance under grow-out farm conditions.
Experimental bioassays were conducted using Specific Pathogen Free (SPF) P. vannamei of 40 family lines (20 fast growth and 20 slow growth lines) and an immersion challenge route using V. parahaemolyticus at 4.95x107 CFU/ml. Each family line had three replicate tanks and ten animals/ tank (20 L size tank). Animals received a binary mortality phenotype at the end of three days of challenge. Genetic parameters were estimated using a mixed threshold animal model, with a random additive genetic effect modeled for either pedigree or single-step genomic predictions.
The heritabilities (SE) for the first AHPND challenge were estimated to be 0.38(0.08) for the combined slow and fast growth lines. The within-line heritability was 0.16(0.07) and 0.14(0.06) for the slow and fast growth lines. For the second AHPND challenge, heritabilities were 0.31(0.05), 0.47(0.13), and 0.26(0.08) for the combined data, slow growth, and fast growth lines, respectively. The correlations between breeding values predicted with pedigree and the family means were above 0.85. Genomic breeding values (GEBVs) were calculated and allowed for predicting individual performance of SPF shrimp that were not exposed to bacterial challenges. Moreover, GEBVs identified differences between individuals within families, allowing more accurate selection tools. The correlation between growth and mortality performance across families was not significant, indicating the absence of selection trade-offs. However, more data are needed before conclusions.
We are now expanding the genomic evaluation to include genotype data for animals used in the second AHPND challenge. The analysis will include a validation of the GEBVs and enable us to evaluate the estimation of response to selection and define the future steps for a genomic selection program. Additionally, a trade-off analysis between disease resistance and growth will be made to ensure that selecting disease-resistant individuals will not impact growth negatively. Finally, we will correlate GEBVs with histopathology data and quantitative load of V. parahaemolyticus in the experimentally challenged animals to better understand the genetic effects of AHPND tolerance on bacterial replication and pathological manifestation in shrimp.